Mouser electronics - What Every Electronics Purchaser Should Know

Back to Basics: What Every Electronics Purchaser Should Know MOSFET Zigbee

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Foreword The sourcing of advanced components and modules needed for modern electronic designs can be a complex process, with a variety of different obstacles to overcome. Engineering staff may have specified a particular bill-of-materials (BOM), based on performance benchmarks and breadth of functionality. However, they do not always fully appreciate that their colleagues over in the purchasing team have to take an array of additional, more commercially and logistically oriented factors into account too. It is, consequently, a much tougher job than most of them actually realise!

By giving purchasing managers and procurement professionals access to a greater technical knowledge base, they would be in a far stronger position - able to have more meaningful discussions with their engineer counterparts, so that the optimal component choices could be made that met all the necessary criteria.

It was this that prompted Mouser Electronics, as part of its ongoing drive to bring new dimensions to its customer engagement and ensure the best possible user experience, to create the following ‘Back to Basics’ guide.

The core objective of this publication is to compile a comprehensive, continuously-expanding resource that purchasing staff can refer to when in need of more information on a particular technology area, or in order to find out what relevant alternatives might be available. In addition, it will present valuable advice to help tackle other important supply chain challenges - such as end-of-life (EoL), component traceability, conflict minerals, e-waste, the threat of counterfeiting, effective use of sourcing online tools, better inventory management, automated order processing, etc.

Mouser Electronics would like to get your input on this too - so if you have ideas about what further subjects should be covered, then contact us at buyersguide@mouser.com

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Contents 05 Wireless Technology 09 Connectors and Cabling 12 Key Connector Types 16 Display Technology 18 Touchscreen Technologies and Other Display Accessories 20 Power Management 24 Thermal Management 27 Microcontrollers 30 Data Converters 35 Operational Amplifiers 39 Glossary 42 Redefining Distribution

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Communication Technologies

Wireless Technology There are many different wireless technologies in use allowing devices to talk to each other. These have different characteristics in terms of speed, distance and power consumption that make each one suited to a particular set of applications. This chapter will discuss some of the main protocols being employed now and some that are emerging onto the market.

Ubiquitous Wireless Networking

With the possible exception of cellular communication, when people generally think of wireless technology today it is probably Wi-Fi that they are most familiar with. This is hardly surprising as widespread rollout means that Wi-Fi is now nearly everywhere - in the home, in cafĂŠs, in hotels, in our cars and at our workplaces. Wi-Fi creates a wireless local area network (WLAN) which can be used by devices such as personal computers, printers, games consoles, mobile phones, smart TVs and all manner of household appliances. These all connect to one another via an access point, which in turn usually links the network back to the Internet (as shown in Figure 1). Wi-Fi can also be used to create an ‘ad-hoc’ network where devices talk directly to each other instead of via an access point.

Modem WiFi Router

Internet Figure 1: A typical Wi-Fi network Wi-Fi has a long history and there have been many improvements to the technology resulting in faster data rates, extended range and greater levels of security. The hardware and communication protocols are defined in the IEEE standard 802.11. A trade group known as the Wi-Fi Alliance define certification procedures and interoperability testing. The products and systems that companies produce need to pass these in order to display the Wi-Fi logo.

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Communication Technologies Wi-Fi relies on two different frequency bands, 2.4GHz and 5GHz, and, generally speaking, has a range of around 10m to 30m indoors (where it is limited by obstructions such as walls). This can be made worse by interference, as the 2.4GHz band is utilised by many other devices such as baby monitors and Bluetooth®-enabled equipment.

The various versions of Wi-Fi are represented by the revisions of the standard in which they were initially defined. The first version to be widely adopted was 802.11b. New devices will always support all the previous standards as well as the latest. The current standards are: • 802.11b - the basic 2.4GHz standard.

• 802.11a - the initial 5GHz standard providing higher speed but more limited range.

• 802.11g - a faster version of 802.11b, which is up to three times faster due to the way data is encoded.

• 802.11n - which uses multiple antennas at 2.4GHz and 5GHz to do ‘beamforming’ that directs the signal at a target device, providing increased speed and range (up to 70m indoors).

• 802.11ac - which allows more antennas with new encoding schemes to deliver much higher data rates at 5GHz. • 802.11ax - implementation of equipment based on this technology has now begun. It offers the potential to quadruple data throughput and support far greater user densities, thanks to more efficient use of the available spectrum.

Designers of devices that need to support Wi-Fi can buy ready-made modules with all the RF circuitry, including antennas and a microcontroller, with software to manage the communication. These modules are certified by the manufacturers, making it simple to subsequently add Wi-Fi to a product.

Wireless for Personal Networks

Another very common wireless technology is Bluetooth®, which was designed to replace wired connections between nearby devices - creating what is usually referred to as a wireless personal area network (WPAN). It uses the same 2.4GHz frequency band as Wi-Fi but works over much shorter distances and lower data rates in order to reduce power consumption. As there are some security weaknesses associated with it, it is often recommended to only turn on Bluetooth® when it is actually required.

Some typical applications for Bluetooth® include: •C onnecting a phone and wireless headset - this was one of the first uses to become popular and drove initial Bluetooth® sales.

•L inking a phone and car audio system to allow hands-free calls and music to be played.

•P laying music through wireless speakers.

•P airing wireless fitness trackers or watches to a mobile phone or computer.

•U sing a wireless keyboard or mouse with a computer.

•T ransferring files between devices.

New applications, such as wearable electronics, e-medicine and the Internet of Things (IoT) are set to drive future demand. In 2016, annual Bluetooth® IC shipments were around 1.6 billion units, this rose to just over 3 billion last year and market analyst firm ABI Research predicts this will rise to 5 billion by 2021.

The Bluetooth® standard is controlled by an industry body called the Bluetooth® Special Interest Group (SIG). The Bluetooth® SIG manages the development of the standard and qualification programme. It also owns the trademarks so the name and logo can only be displayed on certified devices. Interestingly, Bluetooth® technology is named after a 10th century Danish king, Harald Bluetooth®, who united the tribes of Denmark into a single kingdom. The logo is based on the runes for his initials.

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Communication Technologies

Low-Power Networking for Control

Zigbee and Z-wave are two very low-power wireless communication technologies that are intended mainly for applications such as home automation, where sensors and control devices need to have a lifetime of years with just a very small battery powering them.

Both systems are designed to be low-cost and have minimal power budget. Because of this, they are relatively low bandwidth and short range (tens of metres, line-of-sight). They are suitable for low data rate applications with intermittent data transmission such as intruder or smoke alarms, industrial controls, light switches, thermostats and similar sensors and controls.

Energy Monitoring

AP

3G/LTE Network

ZigBee Gateway

Home Controls

HVAC Controls Security & Surveillance

Figure 2: Use of wireless in home automation systems The Zigbee specification is an open standard defined by an industry group, the Zigbee Alliance.

All designs need to pass its validation tests. In contrast, Z-Wave is a proprietary system originally developed by Sigma Designs, but with the IP now being owned by Silicon Labs and Mitsumi serving as a second source supplier in some cases. It has slightly lower bandwidth, but longer range than Zigbee. As it is simpler in nature, it may be easy to develop a system using Z-Wave, however, this also means that it is not as flexible as Zigbee.

Contactless Identification

Radio frequency identification (RFID) and its subset, near-field communication (NFC), are two technologies that are widely used for product tracking, access control systems and other contactless applications.

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Communication Technologies RFID tags are widely used for stock control and logistics, allowing the position and movement of items to be monitored through a production line or warehouse, and preventing theft. These are the same sort of tags that have to be removed or neutralised by a scanner when buying goods in a shop.

This technology is also found in access control cards, e-passports and for payment systems.

RFID uses electromagnetic induction between loop antennas in the tag and a reader. Tags are data stores that can be accessed by the reader. There are two types of tag, namely: •A ctive tags - which have a battery to generate the radio signal, allowing greater range, but increased cost and limited lifetime.

•P assive tags - which use the energy in the signal picked up by the tag’s antenna to power the device, thereby limiting the range of operation, but making the tags much cheaper.

There are a variety of different RFID standards created by industry organisations and national bodies, as well as numerous proprietary systems. Furthermore, countries do not all use the same radio frequencies - so a European tag might not work in the USA, for example. There is limited security designed into RFID tags and there are privacy concerns about the ability to track people who are carrying or wearing tagged products.

The NFC standard is defined and promoted by the ISO and various other industry bodies, including the NFC Forum. It extends the technology behind RFID to allow more flexible communication between devices. A device can act as both a tag and a reader thus enabling two-way, peer-topeer communication. NFC includes greater security than RFID, thereby making it more suitable for contactless payment and access control functions. NFC capabilities are now incorporated into almost all smartphone models, which enables contactless payment and the exchange of information between handsets.

High-Speed Wireless Communications Replace Cables

There are a number of new and emerging technologies aimed at replacing the cables that connect video and audio devices, such as DVD players and TVs. Examples are WiGig and WirelessHD. These systems use much higher frequencies than Wi-Fi to provide elevated data rates. At 60GHz the signals won’t pass through walls, or even people, so they are limited to line-of-sight operation between devices, with a range of about 10m. WiGig can transfer 1,000 photos between computers in a period of 5sec. Uploading 2min HD video recordings from a camcorder would take about 1min over a Wi-Fi connection, but a mere 3sec over WiGig. The WiGig standard is managed by the Wi-Fi Alliance but was given a new name to highlight the fact it is not backward compatible. It is intended to complement Wi-Fi rather than replace it. WirelessHD is a proprietary protocol targeting the same applications and with similar performance and range characteristics.

There are many other wireless communications in use and being developed. Only time will tell which of these will come to be as ubiquitous as Wi-Fi or Bluetooth® in their application areas. One of the challenges that procurement staff face is the uncertainty about which emerging standards will actually become established. Though engineers will look to gain a performance advantage through specifying a certain wireless chip for their design, this will not come to fruition if the chosen technology fails to gain widespread deployment - with cost penalties arising as a consequence.

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Mechanical

Connectors and Cabling Interconnection is an essential element of almost all electronic systems, whether used to provide internal connectivity between sub-systems or an interface to the outside world to allow engineers to deliver power and/or data. The selection of available connectors is huge and constantly changing as suppliers develop new technologies to meet the latest market demands. This chapter of our purchasing guide will look at the major connector types and give some guidance on points to be aware of when selecting a specific connector solution.

PCB Connectors

This very broad category includes both board-to-board and board-to-cable connector components.

These connectors are almost exclusively used inside the system and allow the system to be configured as modules, thereby enhancing manufacturability and serviceability aspects. There is a wide variety of options available. These range from very low-cost pin-and-socket solutions to very high density, low profile solutions for high performance requirements in space-constrained environments. Other options available include the ability to mechanically attach the connector to the PCB for applications that are susceptible to shock and vibration. Some provide a latching function, or an eject function for de-mating, while others rely on mechanical spaces between the PCBs to hold the assembly together.

Specialist versions are now available to be able to transmit power, RF or other signals between boards. If using these connectors to transmit power, careful attention should be paid to the size of the conductors in order to ensure that the temperature of the connector does not increase unacceptably during operation.

The materials used in the connector should also be considered carefully. The plastic insulator must be compatible with any soldering and cleaning processes in use as well as providing sufficient electrical insulation for any high voltage signals. The plating on the pins is often pure tin, so as to comply with RoHS requirements. This is perfectly acceptable for most use cases where the connectors are mated infrequently, but if the connector is to be cycled frequently then the addition of plating must be considered.

Wire-to-board connectors are similar to board-to-board except that the mating (usually female) part allows the attachment of cables so that signals can be connected to other parts of the system (including front panels or a PCB where direct board-to-board connection is not possible). One hidden cost here can be that of the tooling required to crimp the wires into the connector housing.

Fibre Optic Connectors

Due to the growing need for high-speed connections and a trend towards data security, fibre optic connectors are becoming increasingly popular. Available types include single mode, multimode, small form factor (SFF) and a number of application-specific types (for example, those used in audio applications). The advent of plastic optical fiber (POF) technology has provided the industry with a more cost-effective and easy-to-implement alternative to conventional glass-based optical fiber, especially in applications where high data rates over long distances are not required.

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Mechanical Signal attenuation or loss is a key consideration for fibre optic connectors, both the insertion loss as well as any return loss due to reflections. Many fibre optic connectors include a spring mechanism to ensure that the mating faces (either glass-to-glass or plastic-to-plastic) are pressed together properly.

This thereby ensures that signal integrity is maintained.

Fibre optic connectors are often used outdoors and may be located underground or exposed to the elements. If it is not possible to source a suitable sealed connector then customised protective enclosures are necessary. These will, of course, add cost and complexity to the whole assembly process.

Military Grade Connectors

Reliability is, without question, a paramount concern within mission-critical military grade connectors.

In general, the size and shape of military connectors as well as sealing requirements, reliability and performance are all defined by a series of standards.

The outer housing, locking mechanism and sealing are generally all stipulated in the standards and compliance is of primary importance to ensure connectivity with other equipment. Size and weight also need to be factored in as certain high-reliability applications are impacted by these aspects, especially in relation to avionics or portable equipment.

While the mechanical facets are very heavily controlled, there is more flexibility in the type and nature of contacts used within the housing. Specialist military connector suppliers can populate a wide array of different contacts into a standard shell to support various application requirements. Common examples of contact types include signal, power, fibre optic, USB and RJ45 but others are also possible.

Cabling

While there are many types of cable on the market, they all share one thing in common - they are designed to conduct power and/or electrical data signals. Some cables may have a single conductor while applications that are more complex may require multiple conductors. Not all conductors in a cable are necessarily the same, some cables have provision for both power and signals.

As applications require ever-higher speeds, so cables become more sophisticated. RF cables are normally co-axial, meaning that the conductor is surrounded by a braided earth screen that shields the signal from interference. In data cabling, pairs of wires are often twisted together (being referred to as a ‘twisted pair’) to preserve signal integrity in applications such as Ethernet.

The size of the individual connectors is often defined by the signals they carry, as well as the length of the supporting cable. In power cables, the ability to transmit power without significant voltage drops or temperature rises is important. In data cables, the acceptable level of signal attenuation is key in determining conductor dimensions.

The physical properties of the cable are also important. The outer jacket may be required to provide physical protection in harsh environments, or be rated to resist chemicals or extremes of temperature and humidity. Some cables are attached to moving parts, especially in robotics, so the ability to withstand constant flexing is important here.

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Mechanical

Supplier Selection

In many ways, general good practices in selecting suppliers apply equally to connector suppliers as they do to semiconductor suppliers. However, when purchasing electromechanical devices such as connectors there are a few points worth bearing in mind.

Numerous materials are used in connectors and cables, including base metals, plating materials, surface finishes, insulators, cable sheathing, etc. Therefore, finding a supplier that makes information on all of these materials easily available will facilitate the process of complying with RoHS, REACH and conflict minerals legislation.

Reliability is key, as many connectors are subjected to harsh environments and user abuse. Detailed manufacturer test data for the specific connector is invaluable, especially for connectors that are frequently mated/unmated, in ensuring that the chosen connector will not compromise system reliability. As engineers are challenged to fit connectors into small spaces without impeding airflow, as well as providing good access for assembly and repair operations, the availability of 3D models for the connector can save design time and mitigate costly mistakes.

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Mechanical

Key Connector Types Board-to-Board:

Sometimes called PCB connectors or headers, these are used to connect PCBs or terminate wires to PCBs. A huge variety of options and features are available. Selecting lower cost plastics or plating can impact on reliability. They may require mechanical supports and crimping tools can represent an additional cost.

Coaxial:

These are most commonly used in high-speed (RF) applications - including TV, cellular and instrumentation. The conductor is surrounded by a shield to prevent noise affecting signal integrity and most types include a latch mechanism. Cable impedance and operating frequency are important selection criteria.

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Mechanical

USB:

Defined by the USB standard, these are now commonplace in portable electronics equipment and computer peripherals - allowing data and power to be transferred. Early versions of the standard require a different plug/socket for the host/peripheral and are available in different sizes (standard, mini and micro). USB Type-C standardises the connector at both ends of a bidirectional cable for convenience, but hardware costs are higher.

FFC/FPC:

This high density latching connector system comprises separate connectors and flat cables, frequently used to connect displays to PCBs. Fine pitch versions (0.2mm) are available for compact spaces and connectors can have up to 260 contacts. There are a wide variety of options - including plating, contact orientation, termination and cable length.

Modular Jacks:

Primarily designed for telephone and data connections, such as Ethernet, these are specified by the number of positions and number of contacts actually fitted. All plugs have a latching mechanism and some sockets include indicator LEDs. These connectors can be referred to as RJ11, RJ14, RJ25 or RJ45.

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Mechanical

Audio:

This describes a wide variety of mostly circular connectors meeting standards such as RCA phono, jack (2.5mm, 3.5mm, 6.35mm), XLR and DIN. Due to wide availability, this genre is often used for proprietary applications other than audio. Normally subject to frequent and rough handling, high quality versions should be sought to ensure reliability.

D-Subminiature (D-Sub):

A very popular latching connector type that can contain from 2 to >100 contacts per connector in up to 4 rows. Available for chassis and direct PCB mount in standard and compact Micro-D versions for space-constrained applications. Wires can be crimped, soldered or IDC press-fitted. A large range of accessories are available to help customise solutions.

Fibre Optic:

Used for high speed, high throughput applications where signal integrity and data security is important. The fixed connector is usually female and the cable is generally male. Inbuilt spring mechanisms ensure that glass / plastic conductors mate properly. If used outdoors then a sealed type should be selected or a sealing boot used.

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Mechanical

Backplane/Card Edge:

High pin count connectors for connecting PCBs to a common backplane, normally at right angles.

DIN41612 and PCI Express (PCIe) are the most common standard, with male types used for the PCB and female types for the backplane. Options include special contacts for power and long or short pins for sequencing power and signals during mating.

Terminal Blocks:

Usually provided for end users to connect discrete wires via a screw-in terminal, push-in or pressto-clamp mechanism. Can be soldered directly to PCBs or clamped to a DIN rail and available accessories include pluggable blocks for multi-wire connections. If used for hazardous voltages then selection of correctly rated types must be ensured.

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Optoelectronics

Display Technology The display is now recognised as a vital part of modern electronics designs. Not only does this provide a way of delivering information to the person operating the system that it has been incorporated into, it may also (in conjunction with a touchscreen) form the basis of a user interface.

This next chapter provides an overview of these different display technologies and describes their respective advantages and disadvantages.

Liquid Crystal Displays

Liquid crystal display (LCD) screens have a layer of transparent liquid crystal material that is located between polarising filters. When a voltage is applied across the liquid crystal layer it changes the polarisation and hence the amount of light passing through. As this depends on light being seen through the LCD it must have either a reflector or a light source (commonly referred to as a backlight) situated behind it.

The first generation of LCDs could only display a fixed range of symbols - for example, the numbers on a calculator. The development of thin film transistor (TFT) displays that comprise a grid of transistors built into the display surface has enabled individual pixels to be turned on and off. This thereby allows the LCD screen to render much more detailed image content. By combining this with coloured filters, to create RGB sub-pixels, LCD displays can be used to deliver full colour images and, consequently, they have been widely adopted for flat screen TVs, mobile phones and computers - as well as, more recently, for the user interfaces in industrial equipment and medical instrumentation.

The backlighting to support these displays can be provided by fluorescent lamps or, increasingly, by light emitting diode (LED) emitters. Using LEDs consumes less power and can provide a greater contrast range by adjusting the light level based on the content of the displayed image. There is some potentially confusing terminology in use, particularly by TV manufacturers, for various types of LCD displays. For several years now, TVs with so-called LED displays have been available. These are actually LCD displays that use LEDs solely for their backlighting.

The key advantages of LCD displays are that they are both lightweight and compact. They are also very energy efficient, which makes them highly suited to portable electronics designs. In addition, they are extremely versatile and can be manufactured in almost any size or shape. Conversely, the main shortcomings of LCDs are their limited viewing angle and poor black level (because the liquid crystals cannot be completely opaque and block out the backlight completely). They are also temperature sensitive - suffering from a loss of brightness or contrast if they are too hot or too cold.

LED Displays

LED display technology initially consisted of small numbers of individual LED devices positioned onto a display in order to enable a limited range of symbols to be produced. They were also restricted to just a few colours - green, yellow and red. The invention of the blue LED in the 1990s allowed full colour displays to benefit from using red, green and blue (RGB) LEDs. The subsequent development of the organic LED (OLED) meant that arrays of very small LEDs could be used as pixels on a screen, thus allowing detailed full colour images to be displayed. Combining these with a matrix of thin film transistors to control each LED would produce active matrix OLED (AMOLED) displays, which enable the realisation of larger, faster displays that consume less power.

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Optoelectronics OLED displays have a number of major advantages over LCD screens. They can be fabricated onto a flexible plastic substrate rather than heavy, rigid and fragile glass. The use of LEDs to create each individual pixel provides much better picture quality - with heightened brightness, stronger contrast and wider viewing angle. They are also significantly more power efficient on average and it is expected that they will soon be cheaper than equivalent sized LCDs when new manufacturing technology emerges (allowing them to be quickly printed onto any surface). The main disadvantage of current OLEDs is that they can degrade over time. This affects blue more than the other colours which means that the colour balance could change, as well as the overall brightness.

Electronic Paper

Electronic paper (e-paper) or electronic ink (e-ink) displays are designed to mimic the effect of ink transcribed onto paper. The first practical version of such technology to appear has made use of a layer of spherical beads - black on one side and white on the other. Each side also has a corresponding electric charge which means that, by applying a voltage, the beads can be rotated to show their dark or light side as required. A matrix of connections enables individual pixels to be changed to black or white. Once the beads have been rotated, they will remain in that alignment even after the voltage is removed. This means that e-paper/e-ink displays are effectively permanent, requiring no power to maintain the displayed image – and, as a result, are very different from LCD and OLED displays, which both require power to maintain a rendered image. Consequently, this makes them very energy efficient in applications that do not require constantly updated dynamic images.

Several other e-paper technologies have been developed over time. These are still mostly based on the concept of moving coloured particles to create the image. Among the advantages of e-paper/e-ink are that displays are easy to read, they have a wide viewing angle and they support very low-power operation. Most types of e-paper can be built on a flexible substrate. They can also be read using ambient light rather than requiring a built-in backlight. This makes them very well suited to e-books, labelling and other relatively static display applications. The main disadvantage of the technology is that it is relatively slow. This means it is not suitable for moving images or interactive user interfaces. It also suffers from ‘ghosting’, where a faint after-image is left on the white background when black pixels are cleared. Though this is temporary and can be removed by completely erasing and redrawing the displayed page, it can result in a noticeable flicker when pages are updated. Coloured e-paper displays are becoming available but are currently very expensive.

Display Quality Issues

When manufacturing a display panel, it is possible that there will be some defective pixels that are either permanently lit or unlit - referred to as ‘stuck’ or ‘dead’ pixels. A panel with a small number of defective pixels may still be considered usable and manufacturers have different policies on how to handle displays that have defects. This can, of course, prove to be a point of conflict between suppliers and their customers. For some products, a defect-free screen may be essential. In other cases, a small number of defects may be acceptable - for example, if they are not close together and not in the centre of the screen.

In order to provide some level of coherency with regard to this issue, the International Standards Organisation has defined several quality classes based on the number of each type of defect allowed per million pixels. These are defined in the ISO 13406-2:2001 standard (which was originally applied to LCD screens, but is now equally relevant to newer technologies such as OLED and e-paper) and the later ISO 9241-302, 303, 305 and 307:2008 standards. Unfortunately, not all manufacturers adhere to these standards (which are, in truth, just guidelines rather than being mandatory) and they may also interpret the standards in different ways.

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Mechanical

Touchscreen Technologies and Other Display Accessories Increasingly, displays are being combined with touchscreens to provide interactive human machine interfaces (HMIs). Not only do these allow better user experiences, they are also advantageous from the OEM’s perspective too, since they offer greater design flexibility and convenience than buttons and switches, as well as enabling more attractive design concepts to be realised. There are four main types of touchscreen technology, each being suited to different application scenarios and budgetary criteria.

Resistive Touchscreens

These have several layers, including two that are made of electrically resistive material with a gap separating them. When the screen is pressed, contact is made between these two resistive layers and, by determining changes in the signal resulting from the resistance alterations, the system can detect the location of the touch point. Resistive systems of this kind are often used in factory automation equipment and point-of-sale (PoS) units in shops because they are both low cost and waterproof. They can be operated when wearing gloves or by using any blunt instrument as a stylus (although they are quite rugged, they can be damaged by contact with sharp objects). The multiple layers involved can, however, reduce visibility of the underlying display - which is a drawback.

Furthermore, the sensitivity of resistive touchscreens is not that high.

Surface Capacitive Touchscreens

Here a sheet of glass has a transparent conducting layer applied to it. When this is touched, the conductivity of the user’s skin changes the electrical properties of the conducting layer. By measuring the changes in capacitance across the screen using an X-Y grid of wires, the point where it was touched can be determined. Capacitive touchscreens are sensitive to touch, so no pressure is required. They cannot be operated while wearing gloves and call for a specially designed stylus.

The capacitive layer can be directly integrated onto the LCD or LED display so that there are fewer layers involved. This results in better visibility and greater accuracy than that delivered by resistive touchscreens.

Projected Capacitive Touchscreens

The robustness issues of surface capacitive and resistive touchscreen mechanisms led to the development of projected capacitive (PCAP) technology. Here the touch sensor can be placed behind a relatively thick protective screen. This makes PCAP based touchscreens suitable to be implemented in environments that are more operationally demanding, such as industrial automation - where they could potentially be exposed to oil, grease and water ingress, as well as the effects of shocks and vibrations - or in places where surfaces need to be cleaned on a regular basis, like food processing and healthcare. Touchscreens employing certain types of PCAP technology can be activated by operatives wearing thick gloves, again making them highly appropriate for use in medical and industrial settings. They also have the advantage that they can support multi-touch operation and gesture recognition.

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Mechanical

Substrate containing X electrodes

Adhesive layer

Substrate containing Y electrodes

Grid of electrodes in X and Y directions

The greater the density of the electrodes the higher the resolution of the touchscreen

Protective cover

Figure 1: Construction of a projected capacitive touchscreen There are several construction methods that PCAP touchscreens can follow. The most basic type consists of a layer of indium tin oxide (ITO) being deposited on the underside of the glass screen. This is the method generally used in smartphones and other items of portable equipment. It is very cost effective, but only valid for small format displays (as it is not particularly scalable, since noise levels increase with touchscreen size) and designs where a very thin protective glass layer is needed for the screen, as the capacitive field generated is relatively weak. Larger form factor PCAP touchscreens will rely on arrays of electrodes arranged vertically and horizontally in order to form grids, the density of these grids defining the touchscreen’s resolution. These will either use the principles of mutual capacitance or, conversely, self-capacitance - the latter proving to be more sensitive and former exhibiting greater degrees of accuracy.

Additional Aspects

Other important factors when looking to procure touchscreens for electronics equipment include privacy filters, anti-glare film, optical bonding, etc. Privacy filters are of vital importance where the security of the information being displayed needs to be upheld, such as bank account details on ATMs or patient records on monitors in hospitals. By applying a filter with louvres to the set-up, the display’s field of view (FOV) can be restricted so that only the intended operative or customer can see what is being rendered (and preventing anyone that is peripheral to this from doing so). For outdoor deployments, such as public information systems or digital signage equipment, where sunlight may be incident on the display, anti-glare/anti-reflection measures will need to be considered in order to maintain the optical integrity - thereby ensuring the user can see what is on the display and touch appropriate parts of the screen accordingly. An anti-vandal coating might also be needed if the system is meant for unsupervised use in places where it could be at risk of damage. With optical bonding, a suitable adhesive is applied between the protective glass and the display surface, so as to remove the air gap. This improves the performance of the display or touchscreen assembly. It also makes the assembly sturdier, thus ensuring long term operation, and eliminates the possibility of condensation building up on the underside of the protective glass, which could prove to be an irritation to users.

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Power Technologies

Power Management This chapter will give a summary of the many different discrete and IC devices that are now employed in modern power electronics designs. These will range greatly in complexity. We will start off with simple two-terminal devices, such as diodes, then move through the various types of three-terminal transistors that are available. After that we will look at DC/DC converters and finally focus on power management ICs. Clearly, this gives us quite a lot of ground to cover - so let’s push on.

Diodes

A diode’s function is to pass an electrical current in one direction only, blocking it in the other direction. This means that it effectively acts like a ‘non-return’ valve in a plumbing system. It is very useful in rectification - where an alternating current (AC) needs to be converted into a direct current (DC), as shown in Figure 2. They are also of value for performing switching functions. When specifying such devices, the key characteristics to consider are their current handling and the reverse voltage they can withstand.

In a static situation with current flowing, the differentiator between diode types is the forward voltage drop (which causes power losses to be witnessed). Conventional diode types will drop more voltage than Schottky types (which are used in high-speed switching), but Schottky diodes generally withstand less reverse voltage than conventional types before breakdown occurs.

In a dynamic situation, when the diode is switching from conducting to blocking, the differentiator is speed. Schottky diodes are always fast, but conventional types can be either slow or fast (with fast types losing less power in the process of switching). The new semiconductor materials that have now emerged, namely silicon carbide (SiC) and gallium nitride (GaN), enable diodes to be produced with a better combination of speed, temperature rating, reverse voltage withstand and forward voltage drop - though this all comes at a higher unit price.

Another common diode type seen in power applications is Zener diodes. These devices are used as voltage references or transient voltage clamps. They block reverse current up to a specific voltage level; beyond that they permit current flow to occur. When specifying such devices it will be the reverse breakdown voltage that is the deciding factor.

Conventional Diode

Schottky Figure 1: Main diode types

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Zener

Power Technologies

Figure 2: Schematic Showing Rectification Process

Power Transistors

One of the roles of transistors is a controlled switch. Generally, they have three terminals with a small signal being used on one pin to control a high current between two other pins. The current can be adjusted with a varying control signal or the transistor can act like a switch (with a hard OFF or ON relating to a low or high signal on the control pin).

NPN

PNP Figure 3: BJT types

Bipolar junction transistors (BJTs) are common at low power levels, but they are rarely used today above a few Watts. Their control pin is a ‘base’ connection and the controlling signal is a current. The ‘collector’ and ‘emitter’ pins pass the controlled current. Basic ratings are current handling, voltage withstand when OFF, power handling, speed of operation and current gain (which is the ratio of the controlling to the controlled current). At high current levels, the power lost by supplying current into the base can be substantial. BJTs come in two main forms, NPN or PNP, referring to the polarity of the controlling and switched voltages.

N-Channel

P-Channel

Figure 4: Power MOSFET types

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Power Technologies Metal oxide semiconductor field effect transistors (MOSFETs) are, just like BJTs, generally threeterminal devices, but the controlling pin is a ‘gate’ where a voltage controls the current passing through the ‘drain’ and ‘source’ terminals. Basic ratings here are current handling, voltage withstand when OFF and power handling capability. A key attribute, and one that is often a priority when sourcing MOSFETs, is the resistance between drain and source while in operation. This is known as the on-resistance and is denoted as RDS(on). It gives an indication of the intrinsic power loss within the device (that cannot be avoided whatever the operating conditions are). Another parameter that needs to be considered is the total gate charge Qg(total) as it quantifies the gate drive circuit losses during high frequency switching. MOSFETs are preferred at high power levels because their losses are much lower than equivalent BJTs. In addition, they can generally operate at higher frequencies.

The main MOSFET types are N-channel and P-channel, enhancement mode and depletion mode.

These define polarity of voltages around the device and whether it is normally ON or OFF as a switch.

Unlike BJTs, MOSFETs can conduct in either direction between source and drain when ON. Insulated gate bipolar transistors (IGBTs) are a combination of BJTs and MOSFETs, with a gate pin controlling the current through the emitter and collector pins (much like in a BJT). Quite an old technology, IGBTs are only used as switches, not as ‘linear’ devices (which we will learn about next) and are fairly slow in operation, limiting their deployment to switching frequencies of up to about 50kHz. Their power handling is extremely good though (supporting currents of more than 400A and voltages over 5kV), so they are widely used in applications such as traction, grid-tie inverters and high-power motor control.

Thyristors, which are sometimes referred to as silicon controlled rectifiers (SCRs) or triodes for alternating current (TRIACs), also feature in high-power circuit designs. These are latching semiconductor switches controlled by a gate pin. SCRs only conduct in one direction, while TRIACs can conduct in both directions.

IGBT

SCR Figure 5: IGBTs, TRIACs & SCRs

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TRIAC

Power Technologies

Wide Bandgap Technologies

Strictly speaking, Silicon Carbine (SiC) and Galium Arsenide (GaN) are fabrication technologies that can be applied to any semiconductor device, such as diodes or transistors (like MOSFETs). Most industry analysts predict that the majority of uptake in the future will be in relation to MOSFETs. When these wide bandgap semiconductor technologies are employed, they deliver faster switching speeds, higher operating temperature levels and considerably lower power losses than traditional silicon-based devices. This results in them being more power efficient and also boosting performance. However, the expense of the fabrication processes associated with these devices is still high, leading, as already mentioned, to elevated unit costs (although admittedly these are dropping all the time). Specifying them in more cost sensitive application areas will consequently be hard to justify at this point.

Power Management ICs

In power electronics, general purpose ICs are used for many different functions, however, the main class is involved in the controlling of the power conversion stage - which can be for AC/DC, DC/ DC, AC/AC or DC/AC conversion. There are a multitude of common power conversion methods in use (linear, buck and boost being the most popular). Every one of these requires different control methodologies, with specific ICs suitable for each being supplied by numerous vendors.

Linear control ICs can be simply controllers, or alternatively they can include the controlled transistor (such as a MOSFET) as well - in this guise they are often called three-terminal regulators. In switched mode power conversion, control ICs are used to drive power transistors which can be included in the IC. Sometimes, multiple channels of outputs can be simultaneously controlled. There are, in addition, many ICs available that perform ancillary functions specific to power - such as synchronous rectifier or current sharing controllers.

Power control ICs are categorised by their application rather than their electrical ratings - so, for example, there are ICs for AC/DC power factor correction (PFC) control or for point-of-load (PoL) converter control.

Often there are equivalents between manufacturers, but if there is not a shared manufacturing licence, there are likely to be detail differences that could cause incompatibility in practice. As a consequence, care should be taken when considering these as a potential alternative source.

Power Component Package Options

Although surface mount packaging is commonplace, power components are still seen with throughhole terminations, often because their power dissipation levels are so high that they are mounted to heatsinks as opposed to PCBs. However, as technology evolves and efficiencies increase, more power devices are available in gull-wing, ball grid array, land grid array and other proprietary packages. Lower power devices are shipped in chip-scale sizes and there are often provisions in the package (such as copper lands) to lead away excess heat to PCB tracking.

IPAK

DPAK

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SOT-23

SOT-223

Mechanical

Thermal Management Thermal management is becoming an increasingly important aspect of modern product design.

Engineers are now being challenged to get ever greater levels of performance out of their designs, while ensuring that only minimal space is being taken up.

Though using efficient components and topologies - so that heat is not generated in the first place - is the best approach, inevitably some form of thermal management is often going to be required for a large proportion of applications. Given the general trend to reduce size, weight and power (SWaP), careful selection of the right mechanism for dissipating heat can be critical to the success of a product in the market place.

Cooling methodologies will basically fall into two main categories. These are: • Passive - In which heat is conducted or radiated without moving parts.

•A ctive - Otherwise referred to as ‘forced air’. This uses an active component, such as a fan or blower, to create an airflow.

In some cases, both passive and active methodologies may be combined.

In this chapter, the most popular types of cooling available will be described and some guidance will be given on aspects to consider when purchasing thermal management solutions.

Heatsinks

As every application is different, it is not surprising that the choice of standard heatsinks on the market is almost limitless. Then there is the option of designing a full custom solution as well. In principle, heatsinks are very simple - they are shaped pieces of metal that are attached to a hot device (such as a processor chip) and then radiate excess heat into the ambient air, thereby cooling the device.

For standard semiconductor package types, including the TO-xxx packages commonly used by discrete, stud-mounted devices such as IGBTs and even processors or graphics ICs, standard offthe-shelf heatsinks are available. They may even be supplied as accessories by the semiconductor manufacturer or its distributor.

When specifying a heatsink there are a number of parameters to be considered. The key parameter is the thermal resistance of the heatsink (which is measured in °C/W). In simple terms this means how much the temperature of the heatsink will rise for each Watt of waste heat that it needs to dissipate.

Just about every aspect of the heatsink design will impact on this parameter and, as always, tradeoffs will be needed.

The most common material for heatsink construction is aluminium although aluminium alloys, copper and even ceramic heatsinks are also available. In general, the better the performance, the higher the price so it is always wise to specify the lowest performance material that the application will allow.

The more surface area that a heatsink has the better it will dissipate heat. For this reason, heatsinks are often elaborate shapes - including vanes and ridges to increase the surface area for a given volume. Provided the heatsink will fit the available space and the thermal resistance is adequate for the application then the shape or number of vanes is not a primary concern.

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Mechanical There are various methods of mounting heatsinks to the device to be cooled (more detail will be given on this later). These include mechanical fixings, such as machine screws, as well as thermally conductive adhesives. While there may be only a small additional cost for the adhesive or screw, there can be a significant cost impact on production, due to adding in another process, and this should be kept in mind when selecting a heatsink. Safety is always a concern too. Where a surface may get very hot, appropriate warning labels should be provided. This can, of course, further increase the overall cost.

When mounting a heatsink it is very important to ensure that no gaps exist between the device to be cooled and the heatsink mounting surface, as this will clearly impair its effectiveness. The larger the surface, the more likely this is to be an issue, due to manufacturing tolerances. Specifying small tolerances is prohibitively expensive. To address this, a range of thermal pastes are available along with thermally conductive adhesive pads, often known as ‘gap pads’, plus thermal adhesives. All of these help to ensure that there is a good mechanical and thermal bond between the device being cooled and the heatsink.

Fans & Blowers

In applications where the heat build-up is more than can be addressed through passive approaches, or where space constraints leave too little room for a heatsink to be accommodated, then active devices, such as fans or blowers, are commonly used. In essence, fans and blowers are very similar; a blower is simply a fan with some form of cowling added to direct the airflow into a more controlled stream.

Fans are often used in conjunction with heatsinks by blowing air over the cooling surfaces so as to amplify the effect of the heatsink. This creates a stronger cooling mechanism, albeit at a cost.

The primary parameter for a fan or blower is the amount of air it can move. This is most commonly measured in cubic feet per minute (CFM) although linear feet per minute (LFM) and metric equivalents are also used. The amount of air that a fan or blower can move is dependent on a number of other parameters. These include the size of the fan and the speed of rotation.

As active devices, fans require power to operate. This can be anything from a few DC volts right up to mains AC voltages. Generally, it is best to select a fan that will operate on a voltage that is readily available within the system as generating a voltage specifically for the fan means modifying the power supply, which consequently adds cost and also uses up space. As fans consume power, they will impinge on the overall system efficiency by drawing power that does not contribute to the functionality of the system. If system efficiency is critical and a fan is unavoidable, then modern brushless DC (BLDC) motor-based fans operate with greater efficiency than their brushed counterparts.

Reliability is often an issue with fans and blowers as they are mechanical in nature and have numerous moving parts. As a result, they will tend to fail before the electronics that they accompany.

In order to extend the useful operating lifetime of equipment, fans are commonly designed so they can be easily field-replaceable, although there are cost implications (as this may necessitate special mounting hardware and a connector for the power cable).

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Mechanical In many applications, fans are speed-controlled to maintain a certain temperature within the system without using more power than necessary. Some fans include control electronics, which saves space on the main PCB, but increases the cost of the fan. If the fan is likely to be replaced during the life of the equipment, then including the control electronics on the main PCB and selecting the simplest fan type will help to reduce maintenance costs.

Fans create some ambient noise when operating which can be a concern in some environments, such as offices or hospitals. In industrial or outdoor environments, this is much less likely to be of concern. Fans are rated (in dBA) so that quieter units can be selected. Of course, these are generally slightly more expensive.

One downside of fans is that they can potentially draw dust and debris into the equipment, which can lead to premature failure. Filters are available as accessories to prevent the ingress of this kind, but that does increase cost. Safety is, once again, a consideration as moving fans cannot come into contact with fingers. Finger guards are thus a common accessory, although the cost of these can be avoided by punching slots into metalwork if the product uses a custom case.

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Digital ICs

Microcontrollers A microcontroller is the heart (or, more accurately, the brain) of any embedded system. Like the processor in a PC, it executes the software that gives the system its functionality - whether this is a mobile phone, a TV or an engine management system.

The main difference between a microcontroller and the processor in your PC is the level of integration (the amount of functionality that has been packed in). In a PC, components such as the memory, network interfaces and graphics are external to the processor - on the motherboard or add-in cards.

In a microcontroller some, or possibly all, of the memory, interfaces and peripherals will be integrated on the same integrated circuit (IC), or silicon chip, as the processor. The microcontroller is therefore often described as a system-on-chip (SoC). In many cases, no other external devices are needed.

A generic microcontroller block diagram is shown below. This includes a processor with a number of interfaces, flash memory for storing the software and SRAM memory for storing data.

Microcontroller Flash

ADC

Processor

DAC

PIO

Timer

Wi-Fi

System Control

Interconnect

SRAM

USB

Ethernet

Figure 1: Schematic showing the basic functional blocks in a microcontroller

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Digital ICs The peripheral devices may include a variety of interfaces. These might include networking (wired Ethernet or wireless ones, like Wi-Fi or Bluetooth®), analogue-to-digital converter (ADC) and digital-toanalogue converter (DAC) interfaces for connecting to audio devices. Parallel input and output (I/O) signals for connecting to switches and LEDs, serial interfaces (such as USB) and other applicationspecific sub-systems may also be featured. Integrating more of the required functionality has a number of benefits. It reduces power consumption because sending data through the external pins of an IC uses much more power than moving data internally. It is also much faster to access memory if it is on-chip so this also provides a performance advantage. Furthermore, it significantly lowers the total system cost, as there are fewer components required to assemble the complete product. There are several ways in which microcontrollers can be classified. One is by ‘word size’ - the data size that the processor uses. The earliest widely used processors were 8-bit devices. These operate on 8-bit chunks of data, called bytes. Later processors used 16-bit, then 32-bit and 64-bit data. 8-bit processors are smaller and can be lower-power and faster for some applications. For more complex applications involving significant data processing, 32-bit or 64-bit processors will be more efficient.

As technology has advanced and processors have got smaller, there has been a steady move from 8-bit and 16-bit microcontrollers to 32-bit systems, which now make up over two-thirds of the overall microcontroller market. 8-bit processors are still suitable for control of simple interfaces and so some microcontrollers will use a mixture of 8-bit and 32-bit processors - these are referred to as ‘heterogeneous systems’.

Another way of categorising microcontrollers is by the architecture - the type of processor it uses as its foundation. There are two broad classes of processor architectures. These are called: • Reduced instruction set computing (RISC).

• Complex instruction set computing (CISC).

A RISC processor executes instructions that perform a single, simple operation. The instructions of a CISC processor, on the other hand, can perform a complex series of operations. For example, a CISC multiply instruction might read two data words from memory, multiply them and then write the result to memory. To perform the same multiplication, a RISC processor would require two instructions to read the values from memory, one or more instructions to subsequently multiply them, and then another instruction to save the result to memory. The idea is that the simpler instructions mean the hardware can be simpler and faster than a CISC processor and this will offset the fact that more instructions are needed to perform a given function.

There are many different processor architectures used in embedded systems. However, the market is dominated by Intel (x86) and ARM processors. Between them these accounted for 82% of the $15.5 billion total market in 2016. By chance, these are examples of a CISC and a RISC architecture respectively. They also have very different business models. Intel manufacture their own devices for embedded applications (many of these use the low-power Atom processor) while ARM licenses its designs as IP for other companies to use in their own microcontroller chip designs.

Companies that manufacture ARM-based microcontrollers include Atmel/Microchip, Freescale/NXP, STMicroelectronics, Texas Instruments and many others.

The fact that many semiconductor manufacturers use the ARM architecture is an advantage for engineering and procurement teams, because there is a good infrastructure of software tools, middleware, applications, documentation and support available. This is advantageous from a purchasing perspective, as it becomes a challenge for the semiconductor companies to differentiate their products in order to win and retain customers. The ease with which users can switch between different vendors means that pricing needs to be competitive.

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Digital ICs For this reason, some companies, including many who are ARM licensees, have their own proprietary architectures. Some popular examples are: •A VR from Atmel (now part of Microchip). The original 8-bit AVR processor is used in the Arduino development boards. The 32-bit AVR processor is claimed to be exceptionally low-power.

•T he PIC family of processors from Microchip were first designed in 1976 and since then a large number of devices with 8, 16 or 32-bit processors and a wide range of memory and interface options have been developed.

•T he SuperH family from Renesas, which is particularly popular in Japan.

• I nfineon’s TriCore microcontrollers have features specifically designed for safety-critical applications and so are widely used in automotive and industrial applications.

•T he MIPS architecture from Imagination Technologies (like ARM) is licensed as IP. •A RC is another IP processor design available from Synopsys.

All of these are RISC processors.

With so many microcontrollers available, what criteria are used to choose the best solution for a project?

Firstly, the device must meet the basic requirements of the application in terms of performance, memory size, power consumption, integrated peripherals, etc. That will still leave a large choice of vendors with products that could potentially be used. Other factors that will be taken into account are the range and quality of the software and support available (either from the semiconductor vendor or third parties). In some cases, the requirement for software compatibility will limit the choice. For example, if the device needs to run apps written for either ARM processors or the Intel x86 family, then the choice is limited to compatible processors.

In the end, the decision may come down to something as simple as which hardware and software the engineering team is most familiar with. This can help reduce development time and risk of technical issues arising, so should be factored in when purchasing decisions are being made.

The nature of the product may also affect the choice. For example, a low-volume product might use an off-the-shelf circuit board containing the microcontroller and any necessary supporting hardware (power supply, interface sockets, display and so on). This avoids the cost of designing and manufacturing a custom board, resulting in less impact on the budget, a shortened development cycle and quicker time to market. On the other hand, for a mass-produced product, the volume pricing and availability will be critical.

In summary, the microcontroller provides the core functionality of an embedded system and may include all of the required memory and interfaces. With a wide range of products available, the selection process can seem baffling, but will be guided by the hardware and software requirements of the project and the expertise of the team.

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Analogue/Mixed Signal Components

Data Converters Most interfaces connecting to a microcontroller are of a digital nature - for example the USB ports, external memory, etc. These signals switch between two voltage levels representing the binary values 0 and 1. More complex information is encoded as words or sequences of these 0s and 1s.

Sometimes systems need to interface with analogue signals, which can have a smoothly changing range of values. A familiar example is the mobile phone where speech sounds must be converted to digital signals in order to be sent over the network, while at the other end the digital signal has to be converted back to an audio signal. To handle these analogue signals, components are needed that can transform an input voltage to a numerical value and, conversely, convert a digital value to an output voltage. These devices are known as data converters and come in two basic forms.

Digital-to-Analogue Converters

A digital-to-analogue converter (DAC) translates a digital value to the corresponding output voltage (or, in some cases, current). Because the input to the converter is digital, the output will consist of a series of discrete levels rather than a smoothly changing voltage. The signal can be filtered if necessary to smooth out the steps, as shown in the diagram below.

filtered output analogue output

digital values

Time Figure 1: Example of a stepped signal being smoothed out through filtering

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Analogue/Mixed Signal Components DACs are employed in a wide range of different applications. A common one is generating audio outputs for use in digital music players, mobile phones and consumer products. In these, the DAC device operates at a relatively low speed but requires very accurate conversion (to avoid introducing noise and distortion). Another common use is generating the video signals in TVs. These are much higher frequency signals, but do not need to be quite as accurate. There are many other applications such as controlling electrical hardware - for example, the speed of a simple motor (e.g. for driving the cooling fan in a laptop) can be controlled by adjusting the voltage supply.

One of the simplest types of DAC circuitry generates a binary-weighted voltage for each bit of the input. These are then summed to give the output voltage. As an example, consider a 4-bit DAC which can output 16 different levels between 0 and 1.5V. Figure 2 shows how the value 0101 is converted to the corresponding voltage.

voltage for each bit

0.1 0.2 0.4 0.8

digital value: 0 1 0 1

analogue output:

0.4 + 0.1 = 0.5V

Figure 2: Conversion process on a 4-bit DAC device An alternative method is to use a technique called pulse width modulation (PWM). In this case, the output is still a digital signal (a series of pulses). The ratio between the time that the output is designated to 1 (a high voltage) and 0 (a low voltage) is varied so that the average corresponds to the required output voltage. If necessary, the output can be filtered to generate this average voltage, however, in many cases (such as when driving a loudspeaker or motor) the device itself will act as a filter by smoothing out the pulses. As the PWM circuit is entirely digital it is a simple and low cost way of doing digital-to-analogue conversion.

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Analogue/Mixed Signal Components

Analogue-to-Digital Converters

An analogue-to-digital converter (ADC) transforms an input signal (either a voltage or a current) to a digital number that represents its value. The process involved basically converts a smoothly varying signal into a series of discrete samples taken at fixed time intervals. This will inevitably introduce some errors into the signal as the continuously varying input will be converted to a series of steps that are the nearest digital approximation of the input voltage.

analogue output digital samples Time Figure 3: Example of an analogue signal being transformed into a digital one One key use for ADCs is for digitising audio signals - for example, in music recording. This requires accurate conversion to minimise noise and distortion. An important factor is that the signal must be sampled at least twice as fast as the highest frequency in the input, in order to avoid a problem called aliasing, as this causes any frequencies greater than half the sampling frequency to appear as low frequency noise. Another task in which ADCs are utilised is for taking inputs from sensors in scientific instrumentation or lab equipment in order to measure temperature, light intensity, etc.

Converting an analogue signal to a digital value is slightly more complicated than the other way around. As a result, there are many types of converter available, all with different characteristics. One of the conceptually simplest methods is called ‘direct conversion’. This uses an array of circuits to compare the input against each voltage range in the digital representation. Figure 4 shows how this works for a 2-bit ADC.

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Analogue/Mixed Signal Components Input Voltage (0.3V)

Voltage Comparators > 0.75 > 0.5

> 0.25

11

10 01

Select largest value

Digital Output (0.1)

00 Figure 4: Schematic showing direct conversion on a 2-bit ADC Though the technique allows very fast conversion, it quickly becomes expensive and impractical as larger numbers of bits are required. The number of comparator circuits doubles for each extra bit added - so while 2 bits of data needs 3 comparators, 8 bits would call for 255. This would clearly have a huge impact on the bill-of-materials costs.

Other methods use various time-based or iterative processes to find the digital value that matches the input voltage. For example, counting how long an increasing reference voltage takes to reach the same level as the input signal. All these techniques have their own respective trade-offs in relation to accuracy, speed, cost, etc.

Quality & Performance

ADCs and DACs can be characterised by a number of attributes that define the quality of conversion.

The most important factors are the resolution and the speed of conversion. Resolution is the number of discrete levels that the digital signal can represent (basically the number of bits in the digital value).

For example, an 8-bit ADC can represent 256 different input levels (these could be treated as 0 to 255 or -128 to 127), while a 12-bit DAC can generate 4,096 different output voltages. The resolution can also be defined in terms of the minimum step in voltage that can be detected or generated. The maximum resolution is determined by the accuracy of the components used in the converter and the level of noise exhibited, which both limit how small a difference in voltage can be measured. The other important aspect is the conversion speed and sampling rate - in other words, how frequently samples are converted. The speed depends on the type of converter and possibly the number of bits it possesses, especially for an ADC that uses a time-based method to find the value.

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Analogue/Mixed Signal Components

Specifying a Data Converter

Some microcontrollers have integrated ADCs or DACs. For higher quality or faster conversion, however, external devices are likely to be used. The digital interfaces between the microcontroller and the converters usually send the data as a series of bits over one or two wires, rather than an entire word at a time. This is to minimise the number of pins required, which in turn reduces the associated cost and power consumption.

Because the analogue to digital hardware itself is relatively complex, multi-channel ADC devices share a single converter between multiple analogue inputs. Each input is connected to the converter hardware in turn and a corresponding digital value generated. The resolution required will depend on the accuracy that the application mandates. Any noise or distortion created by the inherent errors in conversion must be sufficiently small that they are not significant for the application. For a simple temperature measurement, 8 bits may be adequate and the sampling rate might be only once or twice a second. For high quality music recording, though, 16 or 24 bits could be required.

As noted above, the sampling rate must be at least twice as fast as the fastest change that needs to be converted. For professional quality audio this may be as high as 96kHz. Handling video or radio signals will require even higher sampling rates. Not surprisingly, a high-speed 16-bit converter with high accuracy and low noise characteristics will be more expensive than a slower, low resolution device.

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Analogue/Mixed Signal Components

Operational Amplifiers Operational amplifiers, universally known as op-amps, are general-purpose analogue components that can be used to build many useful circuits. Their popularity as a building block is due to the incredible versatility that they exhibit. By using only a few external components it is possible to create a wide range of different functions.

Vs+ V+

+

V-

-

Vout

VsFigure 1: An operational amplifier

Op-amp Overview

The basic op-amp is a very high gain amplifier with differential inputs and a single output, as shown in Figure 1. Let’s break this down a bit.

High gain means that the output from the amplifier is very much larger than the change in inputs.

Typically, the gain is 100,000 or more. This means that even a very small input will make the output go to its maximum voltage, usually very close to the positive or negative supply voltage. By itself, this may not seem very useful. But we can use a technique called feedback to control the gain and to also change the behaviour from being a simple amplifier. This is where the differential inputs come in.

The op-amp has two inputs which are inverting and non-inverting, usually labelled V- and V+. An input on the inverting input makes the output voltage go in the opposite direction - in other words, an increase in voltage causes a decrease in the output. A signal on the non-inverting input causes the output to change in the same direction, thereby increasing the voltage and causing the output to increase. If the voltage on both inputs changes in the same way, then there is no change in the output. As a result, the output voltage is determined by the difference between the two inputs, hence the term ‘differential amplifier’. This is useful because it allows the designer to use positive and negative feedback to control the behaviour.

In many circuits, a proportion of the output voltage is connected back to the inverting input (as shown in Figure 2). This negative feedback will tend to counteract the changes in the output voltage.

Consequently, the gain of the op-amp with negative feedback will be much smaller than the ‘open loop’ (without feedback) gain and is determined solely by the amount of feedback. For example, if we use resistors to feedback 1/10th of the output voltage, then the gain will be 10.

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Analogue/Mixed Signal Components

+ -

Vin

R1

Vout

R2

Figure 2: Using negative feedback to control the gain The high gain of the op-amp and the low current taken by its inputs means that it behaves almost like an ideal amplifier. As a result, the behaviour and characteristics of a circuit are almost entirely defined by the components used around the op-amp, with little dependence on the characteristics or manufacturing variations in the op-amp itself. This makes the designing and purchasing tasks easier, because the design can be embarked upon assuming that the details of the op-amp itself don’t matter - it is only the values of the surrounding components that define what the circuit will do. Once the initial design is done, the specific details of the op-amp being used can be taken into account to check the precise behaviour of the circuit. This may limit, for example, the frequency range that the circuit will operate over, or it may require some extra external components to compensate for departures from the ideal.

Possible Applications

The basic use for op-amps is just as an amplifier, as shown above. Variations of the same circuit can be used to amplify signals (from a microphone, for example), to invert a signal (by using V- as the input instead of V+), to measure the difference between signals (by applying them to V+ and V-) or to sum signals (by connecting them all to V+, via resistors).

Any signal that is the same on both inputs will not cause a change to the output; this is known as ‘common mode rejection’. This is important because, in many applications, that common mode input is unwanted electrical noise which will be greatly reduced relative to the differential signal. A variant of the basic op-amp which exploits this is the instrumentation amplifier. This adds two further op-amps to the inputs in order to provide even higher common-mode rejection and is used for making very accurate, low-noise measurements.

Another common use of op-amps is to build filters, for example to enhance or remove particular frequencies or frequency ranges. In this case, the feedback network will not be just resistors but will include components whose behaviour is frequency dependent, such as capacitors. By feeding back (negatively) more of the high-frequency components, the gain at those frequencies, and therefore their relative level in the output, can be decreased, producing a low-pass filter. By using time-dependent components to provide positive, instead of negative feedback, op-amps can be employed to build oscillators for incorporation into signal generators. Op-amps are, in addition, integrated into a wide variety of other circuits such as comparators, digital-to-analogue converters (DACs) and analogue-to-digital converters (ADCs), etc.

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Analogue/Mixed Signal Components C = 10nF

R1 = 10k

Vin

R2 = 100k +

A = 10 Vout

0v

R

V1

R

R

V2 V3

R

+

A

0v

Vout = -(V1 + V2 + V3)

Figure 3: Low pass filter and summing amplifier

Sourcing Op-amp Components

Op-amps are available as integrated circuits (ICs) containing one or more op-amps. Because of their small size, the components in the IC are closely matched in their characteristics and are at almost the same temperature. This means the op-amp behaves very near to the ideal.

The best-known op-amp IC is perhaps the ‘741’, originally designed in 1968 by Fairchild. There have been multiple different versions since, from different vendors, so that it has almost become a generic name for op-amps. Although well-known, it is no longer the best op-amp option available. There are now hundreds of different types of op-amps from many manufacturers. These include varieties designed for low cost, high speed, low noise or some combination of such factors. General purpose op-amps can cost as little as â‚Ź0.10 in volume. Conversely, devices for more specialised applications, such as very low noise or automotive qualified parts, can cost several dollars.

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Analogue/Mixed Signal Components Op-amps are manufactured using a variety of different process technologies, such as bipolar, JFET, CMOS or BiCMOS (a combination of bipolar and CMOS). These different technologies each have trade-offs that can make them suited to certain applications. For example, CMOS devices tend to be lower power, particularly at low speeds, and take less current at the inputs. On the other hand, bipolar devices can be faster and have lower noise.

So, if an op-amp is used in conjunction with a sensor, such as a thermocouple, where it is important to minimise input current and the input is changing slowly, then an op-amp with CMOS inputs may be best. For a high-speed, low-noise application a bipolar op-amp is likely to be better. Designers and purchasers will have to consider all the specifications of the device to see which is the best fit for the design.

There is no universal amplifier or manufacturing technology that provides the best solution for all of the many applications in which op-amps are employed. This is why manufacturers continue to provide a multitude of different op-amps, on a variety of semiconductor technologies, with different characteristics for gain, speed, noise, accuracy and so on. In general, there will be multiple suppliers of devices with very similar characteristics. Specifying an op-amp can thus be a long and complicated process.

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Glossary AC Current

Alternating current (AC) is one of the 2 ways in which electrical charge is passed through circuitry.

The voltage in an AC circuit reverses periodically with the current thus changing direction. AC is used in mains power delivery, so as to minimise power losses over long distances.

Analogue-to-Digital Converter

Analogue-to-digital converters (ADCs) are mixed signal devices that take real-word analogue signals (from sensors, etc.) and translate them into digital form for subsequent conditioning/processing.

Bill of Materials

A bill of materials is a complete list of all the different component parts that make up an electronic system and the quantities required for each.

Bit

Presented as a binary digit, the bit is a basic unit used in computing and digital communication applications to denote quantities of information.

BluetoothÂŽ

BluetoothÂŽ is a low power wireless communication protocol for exchanging data over short distances, It occupies the same 2.4GHz frequency band as Wi-Fi.

Byte

Comprising 8 bits, a byte is another unit for measuring quantities of digital information.

Capacitor

Capacitors are passive components that are able to store electrical energy. The amount of energy storage that a capacitor can achieve is known as its capacitance (and is measured in coulombs).

CMOS

Complementary metal oxide semiconductor (CMOS) is a common process technology utilised in the construction of integrated circuits (ICs). CMOS forms the basis of microprocessors, microcontrollers, solid-state memories and various other types of digital device.

Comparator

This is a device that compares 2 voltages or currents and then gives out a digital signal indicating which it deems to be the larger. It has 2 analogue input terminals and a binary digital output.

DC Current

With direct current (DC) the electric charge flows in just one direction, rather than both directions for alternating current (AC). This is the form in which power is supplied from a battery.

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Digital-to-Analogue Converter

The converse of analogue-to-digital converters (ADCs), digital-to-analogue converters (DACs) take digital signals and convert them into an analogue form.

Diode

This is a simple 2-terminal passive component through which current can only pass in one direction.

As a consequence these components are invaluable in the converting of an alternating current (AC) into direct current (DC).

Discreet Device

Discrete devices are ones that effectively have just one sole circuit element - as opposed to integrated circuits (ICs), where there are multiple circuit elements within a single package.

Ethernet

Ethernet is a wireline technology that is commonly used for implementing local area networks (LANs), metropolitan area networks (MANs) and wide area networks (WANs). It is widely deployed in datacenters and increasingly in industrial control applications.

IC

An integrated circuit (IC) comprises a number of electronic circuits etched on to a single piece of semiconductor material. Originally invented in the late 1950s, today many billions of ICs are shipped each year.

I/O

The input/output (I/O) describes the element of an electronics system that allows it to interact with the world around it, passing data to and from the system via various different communication protocol options.

JFET

Junction-gate field effect transistors (JFETs) are straightforward 3-terminal devices that can serve a number of functions - including electronically-controlled switches, amplifiers and voltage-controlled resistors.

LCD

Liquid crystal displays (LCDs) consist of transparent liquid crystalline material situated that between polarising filters. Through these crystals the light provided by a backlight can be manipulated in order to render an image.

LED

Light emitting diodes (LEDs) are optoelectronic devices that give off either visible, infrared (IR) or ultraviolet (UV) light when an electric current is applied.

MOSFET

Metal oxide semiconductor field effect transistors (MOSFETs) are a fundamental ingredient of most modern power system designs. Though very similar to junction-gate field effect transistors (JFETs), these devices have a major difference in relation to the fact that the gate is electrically isolated from the conduction channel.

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Oscillator

Oscillators are a category of passive component with the ability to generate periodic oscillating electronic signals (normally in the form of a sine wave or square wave). They are widely used in many electronic systems for timing purposes.

PCB

Printed circuit boards (PCBs) offer the bedrock upon which complex electronic systems can be constructed - giving mechanical support to the constituent components and the conductive tracks that connect these together.

Pixel

A pixel demarcates a physical point on a display or an image sensor. The number of pixels gives the resolution supported - in simple terms the higher the pixel count, the greater the resolution will be.

RF Technology

Radio frequency (RF) covers all electromagnetic waves found within the 20kHz to 300GHz frequency range and therefore used in radio communication activities.

System-on-Chip

A system-on-chip (SoC) takes the principles of an integrated circuit (IC) and pushes them further resulting in a complete, highly sophisticated electronic system being housed within a single device.

This can result in significant space savings and a reduced bill of materials.

Transistor

Transistors are considered to be the foundation on which semiconductor technology relies. They can be employed in the switching or amplification of electronic signals. The voltage or current applied to one pair of a transistor’s terminals controls the current that passes through the other pair of terminals.

Transistors can either be standalone discrete devices or be combined together in integrated circuits (ICs).

Wide Bandgap Technology

Wide bandgap semiconductor technology represents an emerging branch of power electronics that uses alternatives to traditional silicon (Si) substrates - namely silicon carbide (SiC) and gallium nitride (GaN). These substrates offer various operational advantages in terms of supporting higher switching speeds, greater robustness and elevated power efficiency.

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Redefining Distribution With engineers and procurement managers are forced to deal with shortened design cycles and time-to-market pressures, often combined with harsh budgetary constraints, having a supply chain partner that can be relied upon is more important than ever.

By engaging with the most innovative suppliers from around the globe, Mouser Electronics gains access to the latest product innovations as soon as they are launched onto the market.

Consequently, we have built up a strong reputation for specializing in new product introductions, with more and more items being added on a daily basis.

Drawing from its expansive inventory, with over 5 million parts readily available direct from stock, Mouser is able to give customers exceptional service - benefitting from instant availability and rapid order turnaround. No matter how big the bill-of-materials (BOM) is - from just a few components to several hundred - our team can get it to you in one single shipment, so there is no waiting around for individual items to arrive separately and the project can begin straight away. As there are no minimum order quantities on any product, you can order just as many as you need.

Another key differentiator for Mouser is its unmatched online presence. Through our local websites, a total of 17 different languages are supported. These provide detailed information on all the products stocked, as well as a comprehensive, constantly-updated resource of in-depth technical content to help users to make well-informed sourcing decisions (including articles, blogs, videos and design ideas). Mouser also offers valuable engineer-to-engineer interaction via its LiveChat service, as well as hosting webinars presented by acknowledged industry experts.

Finding particular parts can prove laborious and frustrating. Often it is necessary to open up multiple browser windows that clutter the computer screen and complicate the process. Through the Search Accelerator function developed by Mouser, you simply highlight a part number/keyword on any website and a preview of search results and product details will appear, without the need to leave the page you are currently on - streamlining the whole task significantly. Thanks to FORTE, Mouser’s intelligent BOM tool, it is possible to take imported files containing BOMs then map and customize them accordingly, before processing.

Mouser is fully compliant with the ISO9001 quality management standard - thereby ensuring maximum operational efficiency is always upheld and that the best possible customer experience is derived every time. In addition, the company has AS9100C certification, so that it meets the exacting quality expectations of the avionics sector. Full traceability of all products shipped safeguards against counterfeit items or ones based on conflict minerals entering into the supply chain.

Maintaining close working relationships with our suppliers means that we are able to have greater visibility of the dynamics that are affecting the industry - keeping aware of the new technology trends that are starting to emerge and where new application opportunities lie. To learn more visit: https://eu.mouser.com

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