EEWeb Pulse - Volume 57

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PULSE

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Issue 57 July 31, 2012

Rod Callison Engineering Fellow Raytheon Missile Systems

Electrical Engineering Community

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TA B L E O F C O N T E N T S TABLE OF CONTENTS

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Rod Callison RAYTHEON MISSILE SYSTEMS Interview with Rod Callison - Engineering Fellow

10

Featured Products Pulling Energy Out of Thin Air

12

BY OLIVER SCZESNY WITH ENOCEAN

With energy harvesting becoming a popular power solution, more companies are looking at their surroundings for energy potential.

17

Improved Noise Figure Using an FDA and Input Transformer

BY MICHAEL STEFFES WITH INTERSIL

Deliver high gains with improved signal-to-noise ratio using an input transofrmer into a differntial inverting amplifier design.

RTZ - Return to Zero Comic

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Rod Callison

Raytheon Missile Systems How did you get into engineering and when did you start?

I graduated high school in 1971, but kind of drifted a few years before I decided what I wanted to be when I grew up. When I made up my mind to go back to college in 1977, electrical engineering seemed a logical choice since my strengths had always been math and science. Also, I needed something challenging, and electronics was a fast-growing field.

Being more mature than most of the other students helped me take school more seriously and I did very well. One of my instructors, who taught part-time, and was a full-time

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engineer at General Dynamics, was in a position to recruit the best students and he got me my job at GD in 1979.

Can you tell us more about your work experience before becoming an Engineering Fellow in the RF Center of the Electrical Subsystems Directorate at Raytheon Missile Systems?

When I started with General Dynamics, I was in the “Guidance and Control Dynamics” department.

We were responsible of 6 degree-of-freedom simulations of Standard Missile™ used to predict performance. No one had a computer on their desk. One room in our area had several terminals that tied into a central computer for compilation

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INTERVIEW

The engineers at Raytheon are brilliant and they are always willing to take the time to help someone learn, whether that someone is a new-hire or an old dog like me.

After two years, I wanted to do more design and transferred to the “RF Guidance” department. We weren’t so specialized back then and I had the chance to do digital, analog, and software design. Over the years the defense industry grew, declined, and grew again; divisions of GD split and merged; GD’s missile business was purchased

by Hughes Aircraft who moved to Tucson before being purchased by Raytheon. Departments evolved into more specialized disciplines and I am currently in the “RF Subsystems” department where I do primarily RF analysis.

What were some of your previous positions at Raytheon and the projects you worked on?

I’ve pretty much always been just an engineer. I’ve been the team lead on a number of projects, the principal investigator on a number of IRADs, and am currently the functional manager for the senior members of my department. But, so far, I have successfully avoided any promotion that would take me too far from the technical.

One of my first projects started as an IRAD, for which I was Principal Investigator, and ended as a contract, for which I was the RF team lead. Stinger™ is a lightweight fire-and-forget shortrange air defense missile equipped with an advanced passive two-color infrared/ultraviolet (IR/UV) detector.

We added a passive, two-port, rolling interferometric RF sensor and changed its role to air-to-ground to suppress enemy air defenses by a scout helicopter. I was able to spend one summer flying around the Redstone Arsenal in a UH-1H helicopter during flight tests.

I’ve also worked digital design for the guidance computer on Standard Missile™, a semi-active radar system, and provided analysis for AMRAAM™, an active radar.

What have been some of your influences that have helped you get to where you are today?

That would have to be the people with whom I’ve had the privilege to work. The engineers at Raytheon are brilliant, and they are always willing to take the time to help someone learn, whether that someone is a new-hire or an old dog like me.

Do you have any tricks up your sleeve?

If I could offer one piece of advice, it would be to focus on the basics. I taught electronics engineering parttime at Cal Poly, Pomona, early in my career, which forced me to have a very solid understanding of the basic principles of digital design and analysis. This, in turn, gave me insights into the more complex problems I was encountering at work. Time and time again I’ve

Stinger™

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FEATURED INTERVIEW

and execution of the simulation.

We could pick up the fan-folded printouts a couple of hours after job submittal. This was a big upgrade to the punched cards engineers had been using just a couple of years before.

INTERVIEW

Stinger™

seen engineers skip a fundamental understanding of the system in their impatience to get to the final solution, which seems to elude them.

What has been your favorite project?

The one that first comes to mind was a fairly short task I did several years ago. It was to write an FFT function for the ESSM™ rear receiver.

Processing time was critical, so it would have to be optimized for speed and written in assembly language on a processor we’d never used before, with a development system we’d never used before.

Requirements were challenging, and the schedule even more so.

The program manager needed to know if the processing timeline could be met, and he needed to know by the end of the year. I was working another program and had limited spare time. The PM told me that I was one of two engineers at RMS that could do the job, and the other person was already fully engaged. Of course he had me

hooked at that, whether it was true or not. I fleshed out the requirements; developed, optimized, and tested and timed the code; and delivered a finished product by year end. To my knowledge, that code has never needed modification.

Will you tell us about the two patents related to radar missile guidance that you hold? As well as being member of the Patent Committee?

My first patent was the “Multidimensional in-line linearization PROM”. I was tasked to design a circuit that would linearize commands to an AGC amplifier.

The obvious solution was to map the linearization in a PROM, but the only PROMs I could find had many times the memory capacity than I needed. I hate wasting anything, so I found a use for the extra memory.

The program manager liked the idea and asked me to pursue a patent. I thought it was just good engineering, but I did as I was told and to my great surprise a patent was issued. My second patent was

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Some of my recent career highlights include my promotion to Engineering Fellow, having two patents issued as the sole inventor, and having the opportunity to serve on the RMS Patent Committee.

Three years ago, I had the opportunity to become a member of the Patent Committee at RMS, or as it is more officially know, the Invention Review Committee. This has been a tremendous learning experience. I am in awe of the talent we have at RMS and the innovation

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FEATURED INTERVIEW

an FPGA implementation of the Polar Format Algorithm for Synthetic Aperture Radar. I was working on a project that required such an implementation and asked a fellow engineer, for whom I have the greatest respect and had expertise in that area, if he knew of such a design. Not only was he unaware of any such design, but he had seriously doubts that it could even be done. Nothing he could have said would have been a greater motivator. I made it my mission to prove him wrong. And I did.

INTERVIEW

What are you currently working on?

I support a number of programs, but one of the more interesting things I’m working on is a paper describing a class of biphase codes used in radar pulse compression.

Much work has been done in the past on biphase codes, but this niche seems to have been overlooked.

I’ve written a C program to search for the codes and Matlab scripts to analyze expected performance and characteristics. It’s been fun and educational, and I hope to get the paper published some day.

Can you tell us more about Raytheon and the technology they are developing?

Raytheon Missile Systems is located in Tucson, Arizona, though there are satellite facilities in Kentucky, New Mexico, Arkansas, Alabama, and California. RMS is a premier designer, developer and producer of tactical weapons systems for the United Stated and many allied nations, For more than 60 years,RMS products have been deployed by the U.S. military, and the armies, navies and air forces of more than 40 countries. RMS has developed and supports a broad range of cutting-edge weapons that includes missiles, smart munitions, projectiles, kinetic kill vehicles, space vehicles and directed energy effectors. RMS employs nearly 12,000 people and had $5.6B in revenue last year. Technology being developed includes advanced designs in active, passive, and semiactive radar and signal processing

for missile guidance; directedenergy, non-lethal weapons; advanced electro-optical seekers; and automated factory test facilities.

How does Raytheon continue to be a leading producer of missile systems for U.S. and allied forces, including airto-air, strike, naval weapon systems, land combat?

I believe that Raytheon has a reputation for producing some of the world’s most technologically advanced and capable weapons.

RMS products are meeting today’s threats and we are continually evoling to support the future battlespace and its ever-changing threats. We work closely with our customers to understand their needs so we can develop innovative products and solutions that fulfill our customers’ needs. RMS has a focus on quality, cost, and ontime delivery. We’re committed to providing systems that customers can rely on to perform as needed every time. This promise of Mission Assurance has been proven continually in critical missions and has kept us a leader in the field.

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What is the work culture like at Raytheon?

Raytheon Missile Systems is a blend of cultures from the companies that merged in the 1990’s to form it: Hughes Aircraft, General Dynamics, Texas Instruments, E Systems, and of course Raytheon.

This has given us the opportunity to select the best of each culture to create the environment we have today. Engineers are given a lot of opportunities to shape their careers into what they want them to be.

Raytheon Missile Systems engineers fully realize the importance of helping to foster student interest in math and science. One of the things that RMS Engineers have the opportunity to do is volunteer and visit schools and speak in classrooms year around to help support future generations in science, technology, and math.

What are some new technologies we can expect to see from Raytheon Missile Systems in the near future?

I wish I could tell you. I really do.

But the coolest technologies being developed are held as company

Rod Callison - Engineering Fellow

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FEATURED INTERVIEW

that is taking place in all aspects of engineering.

INTERVIEW

Raytheon is well positioned as a global leader in technology and defense. We have a wide portfolio products and we continue to exceed our customers’ expectations in all of the domains we serve. We will pursue adjacent markets such as foreign sales and partnerships, and commercial sales. Cost, as a design driver, will be given much more weight. There will be an even greater emphasis to delivering on schedule and within budget. We will continue on with our history of innovation that spans more than 90 years.

What challenges do you foresee in our industry?

The biggest challenge to the defense industry is a shrinking

budget for development work. We need to deliver products with the capabilities the warfighter needs at a cost the government can afford.

We cannot cut corners to sacrifice quality or reliability because lives literally depend on our products working as advertised. I believe that at RMS we have the talent to find innovative solutions to these challenges. And engineers love a challenge, right?

way. My wife and I also enjoy traveling and have been fortunate to go on some pretty exciting trips: we’ve visited the landing beaches in Normandy, hiked in the Swiss Alps, cruised the Mediterranean, walked the Great Wall of China, spent the night in a Buddhist monastery in Japan, watched a solar eclipse in Turkey, explored Inca ruins in Peru, and camped on the savannas in Zambia.

What are some of your hobbies outside of work and design?

I’ve spent a week backpacking in California’s Sierra Nevada Mountains nearly every summer for the last 30 years, and hope to continue many more years. I love the feeling of independence, carrying everything I need in my pack, and seeing mountains and valleys that can be seen no other

Is there anything that you have not accomplished yet, that you have your sights on accomplishing in the near future?

In the very near future, my wife and I plan to track mountain gorillas in Uganda. And there are still many other places in the world we’d like to visit. ■

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FEATURED INTERVIEW

proprietary and competition sensitive. Stay tuned and watch for public releases.

erved.

Avago Technologies Motion Control Solutions

World’s Smallest Miniature Reflective 3-channel Encoder Features

Advantages

Benefits

3-channel encoding (AB and I)

Index Signal “I”

No need for separate components to generate the index signal

Miniature size

Surface mount leadless package: 3.95 mm (L) x 3.4mm (W) x 0.95mm H)

Ability to fit into miniature motor designs

304 LPI

High encoding resolution

Various CPR capable by adjusting to the matching ROP of the codewheel

Avago Technologies AEDR-850x three channel reflective encoders integrate an LED light source, photo detector and interpolator circuitry.

It is best suited to applications where small size and space matters!

Built in Interpolator of 1x, 2x, and 4x

1x, 2x and 4x via external pinouts

Base CPR resolution can be interpolated by end user

Applications include medical hand held devices, camera phones, wheel chairs, actuator, vending machine applications, just to name a few.

High operating frequencies: 55 kHz at 1x interpolation

Operating frequencies can be increased by external interpolator pinouts by maximum of 4x

Corresponding high RPM performance with increased frequencies

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Index gating

Options available for both gated and ungated versions

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F E AT U R E D P R O D U C T S This highly functional, multipurpose DC to DC converter delivers 54 V @ 3 A over a wide operating input voltage range of 18 – 72 V with efficiencies up to 91.5 %. The modules are UL approved for PoE applications requiring a DC-DC module that will deliver a 54 V SELV output with a basic insulation system that has an isolation voltage rating of 2250 VDC. The module conforms to the Industry Standard, DOSA half-brick package measuring 58.4 × 61 × 12.7 mm (2.3 × 2.4 × 0.5 inches). Added protection features include input under voltage lockout, output current limiting, short-circuit protection, and thermal shutdown.

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Torque Sensor Transducers with Integral Electronics The new TorqSense RWT410/420 torque sensors, which replace the RWT310/320 Series, feature significant performance gains in resolution, frequency response, reduced sensor current consumption and faster digital data throughput. Transducer overload capability has also been increased to 300%. The series offers a cost effective, non-contact digital rotary torque measurement solution, using TorqSense Surface Acoustic Wave technology, suitable for torque monitoring, testing or controlling drive mechanisms. For more information, please click here.

RF Multi-Measurement Signal Analyzer Vishay Intertechnology, Inc. introduced the industry’s first remote control code learning IC to integrate signal detection and processing into one component. Optimized for universal remote controllers, the VSOP98260 simplifies the code learning process by amplifying and shaping the signal received by the infrared emitter already present in these devices.

The VSOP98620 also can be used in tablet PCs and smartphones that are enabled with an infrared emitter. Samples and production quantities of the new VSOP98260 IC are available now, with a lead time of six weeks for large orders. For more information, please click here.

8M Fast CMOS SRAMs in 44-Pin Alliance Memory is adding to its extensive line of legacy high-speed CMOS SRAMs with two new 8M ICs in the 44-pin, 4-mil TSOP-II and 48-ball, 6-mm by 8-mm TFBGA packages. Featuring fast access times of 10 ns, the AS7C38096A (1M x 8) and AS7C38098A (512K x 16) are pin-for-pin compatible with 4M fast SRAMs, offering twice the density in the same slot. Optimized for commercial, industrial, telecom, and medical applications requiring fast access times, the AS7C38096A and AS7C38098A feature operating currents of 80 mA typical and standby currents of 3 mA typical. For more information, please click here.

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DC-DC Isolated Converter

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EE Making Wireless Truly Wireless: Need For Universal Wireless Power Solution

Dave Baarman Director Of Advanced Technologies

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ARTICLES

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Pulling Energy

TECHNICAL ARTICLE

Oliver Sczesny

Enocean, Inc. - Application Engineering Manager, Co-founder

Hardwired line power has been available in buildings for more than a century. The original two-pin electrical plug and socket was invented and patented in 1904. Now that we are fully immersed in the digital age, we have become more dependent upon energy than ever. Due to the steady increase in energy costs and its converse diminishing supply; innovators have stepped up to create solutions that reduce energy costs and unwanted energy by-products such as CO2 emissions. Buildings have proved a rich habitat for innovation.

Since buildings account for more than 40 percent of the energy consumption in the US, OEMs can capitalize on the shared need for more energy-efficient buildings.

Energy harvesting serves as a great example of one such innovation.. Energy harvesting allows sensor networks to operate independently of an external power supply. This is accomplished by harvesting energy from our surroundings (i.e., from motion, indoor light or differences in temperature). Ten years ago, energy harvesting was a term only known to a small group of specialists; but now there is a diverse range of wireless products on the market that are powered by energy harvesting technology.

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The EnOcean wireless standard, a pacesetter in the field and a catalyst to the development of energy autonomous wireless solutions, serves a host of applications in building automation. In 2012, the open EnOcean protocol was ratified by the International Electrotechnical Commission (IEC) as an international standard (ISO/ IEC 14543-3-10).

The Evolution of Power in Buildings In addition to line and battery power, alternative power sources exist. The last decade has yielded a new generation of energy-autonomous solutions that eliminate the need for wires and batteries as power sources.

Energy harvesting technology enables engineers to think beyond the constraints imposed by traditional power sources.

Negative impacts of Line Power • Particularly in building retrofits, cables are difficult to run to the locations where energy management controls are needed. • Line power is made of irreplaceable natural resources Visit www.eeweb.com

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TECHNICAL ARTICLE

Out of Thin Air

TECHNICAL ARTICLE

Line Power Battery Power

solar

thermoelectric

Energy Harvesting

Figure 1: Sources available for powering building automation devices

such as copper, which is sharply increasing in price.

on a light for instance.

Negative Impacts of Battery Power

• Mechanical harvests energy from motion

• High maintenance – Battery life is typically 6 months to 2 years. This means that if the product is designed to last more than 20 years, then the building owner will have to pay for the upkeep of each device 10 – 40 times during each product life cycle.

• Solar harvests from indoor light • Thermoelectric harvests from temperature differentials

Complete components for a system

EnOcean technology is rooted in the field of sensors which offer numerous possibilities for making systems smarter and more efficient. In buildings, for example, sensors can measure important data from heating or air-conditioning systems to help reduce energy consumption. 20th century sensors are usually wired or battery operated, requiring routine replacement and regular maintenance.

The power for the wireless modules is produced by energy converters, such as an electrodynamic energy generator that makes use of mechanical motion, or a miniaturized solar module. EnOcean modules use this energy to detect information and transmit it wirelessly.

An additional charge capacitor can ensure an adequate power reserve to bridge intervals when little or no energy can be harvested. Much like the power reserve of an automatic clock, it stores energy for phases in which there might not be enough light to operate an energy harvesting module by a mini solar cell. In complete darkness the energy stored will suffice for several days of regular operation. EnOcean-enabled devices are also able to work in difficult ambient conditions. Additionally, modules save energy by executing all operations of sensors and actuators very rapidly, and promptly turning off when they are not needed. For this purpose the sensor modules incorporate special timers that draw only about 20 nanoamperes of current, fully deactivating all other components during sleep phases and waking them again when they are required to operate.

EnOcean engineers solved the problem by using the energy harvesting principle. Wherever there is motion, light, heat or differences in temperature, there exist small amounts of energy that can be harvested. Pressing a button is enough to transmit a wireless signal and turn

Besides harvesting energy from light or motion, EnOcean wireless modules can use heat as a power source.

Electricity is produced from differences in temperature, from the heat of parts of machinery for instance, radiators or even the human body. This means that radiator valves,

• Batteries fill landfills with toxic waste.

Energy harvesting wireless products counter the negative impacts of wires and batteries since the resulting end products do not require wiring or upkeep. Now that OEMs can design past the limits of traditional power sources, they can enter solutions into the marketplace that make a compelling case for integrating impactful interoperable building energy management systems – right now.

Using Energy at Its Source

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TECHNICAL ARTICLE

mechanical

TECHNICAL ARTICLE Radio signals use minimal energy Wireless technology plays a special role in how the energy harvesting modules work. The EnOcean wireless signal is transmitted in the 868 MHz or 315 MHz frequency band. Telegrams are just one millisecond in duration. Although transmitted power is up to 10 milliwatts, the wireless transmission used here only has an energy requirement of 50 microwatt seconds for a single telegram. Requiring so little energy, a sensor can be powered simply by operating a light switch to send the necessary wireless signal to a lamp.

The short telegram is randomly repeated twice in the space of about 40 milliseconds to prevent transmission errors. Transmitting data packets in random intervals make the probability of collision extremely small.

Installation and parallel operation of a large number of wireless switches and sensors in restricted space consequently poses no problem at all. Each EnOcean module comes with a unique 32-bit identification number to exclude any possibility of overlap with other wireless sensors. The range of EnOcean wireless sensors is up to 30 meters inside buildings and 300 meters in the open.

Open-Ended Use Since 2003, EnOcean has been supplying this basic technology for totally maintenance-free sensors and actuators that harvest their energy entirely from their surroundings. Such a system is ready to go right out of the box — OEMs can implement their own energyautonomous applications simply and at low cost, without first accumulating expertise in wireless and energy harvesting. The plug & play approach has fast

established batteryless wireless technology in building automation. A further benefit is the interoperability of products. Standardized sensor profiles enable the equipment of different manufacturers to communicate and operate in one and the same system. In this way it is possible to combine a receiver from manufacturer A with a sensor from manufacturer B for example, plus a functionally identical sensor from manufacturer C.

Smart buildings A major area of application for batteryless wireless technology is building and building services automation.

Products and systems enabled by the energyautonomous wireless technology can be integrated into all common building automation systems – regardless of whether they communicate over LON, KNX, BACnet, TCP/IP or Ethernet. Sustainable energy management concepts can therefore be implemented with reduced effort and expense. Dispensing with wiring means flexibility in where sensors or actuators are located, placing them where they produce the most accurate readings. The data generated can be used for optimum monitoring and regulation of lighting, heating, ventilation and air-conditioning in apartment houses, offices, public or other buildings.

Energy-autonomous building automation solutions range from room thermostats with preset temperature to maintenance-free motion detectors and even window handles. When a window is opened, for example, a radiator can automatically be turned off to reduce energy consumption. Flexible installation without wiring is also an advantage when renovating older properties because units or fixtures can easily be removed or relocated. At the same time, this saves miles of wiring and conduits and significant construction costs. The noise, dirt and dust issues associated with installation are also eliminated.

Focus on Industrial Machinery

Figure 2: Primary types of energy harvesting wireless modules

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In addition to building automation, energy harvesting is beginning to appear in other fields of application. This batteryless, wireless technology is now frequently found in the monitoring and control of large-scale industrial plants. Used to monitor the status of machines, sensors detect data relating to wear and tear, consumption or necessary maintenance intervals, and report any deviations or irregularities. The major advantage is

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TECHNICAL ARTICLE

ventilation flaps or sensors can be deployed wherever heat is available.

TECHNICAL ARTICLE

Fascinating New Applications In the relatively few years since its first appearance, energy harvesting wireless technology has found its way into many applications in many sectors — and there are no foreseeable limits to its further development. As the technology advances, possibilities are emerging in using energy-autonomous, service-free wireless modules for early warning of health risks or in living environments for the elderly, adding extra functionality for more comfort and convenience, security and safety to existing systems.

In agriculture, sensors could be placed over large areas to provide early warning of forest fires, or to ensure that crops are receiving an optimal supply of water and nutrients. Batteryless technology is also suitable for monitoring built fabric such as large bridges. In all these scenarios, wired systems would be too elaborate in their technology and by no means cost-effective. Energy harvesting wireless technology is consequently set to play an increasingly important role in solving everyday problems — whether minor or major — more reliably, more conveniently, more economically and utilizing existing information sources.

The new technology overcomes many of the installation barriers that have stood in the way of making buildings more energy efficient. Building automation products (such as sensors, switches and controllers) based on the EnOcean wireless protocol, are not only interoperable with each other, regardless of the manufacturer; they are also interoperable with other communications protocols such as TCP/IP. The maturation and convergence of the two communication protocols has led to an increase in the energy-saving options available to OEMs. ■

ESK 300C – the ideal entry into EnOcean wireless technology

Limitless Power Generation n

Mechanical harvest energy from motion

n

Solar harvest energy from indoor light

n

Thermoelectric harvest energy from changes in temperature

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www.enocean.com

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TECHNICAL ARTICLE

that the batteryless solutions can be flexibly located — even on moving parts of machinery — and then relocated elsewhere. Plant operators can obtain acutely reliable figures that help prevent production outages.

The innovative technology can also be used to control barriers, open and close gates, supervise cold chains or the condition of containers during transportation.

Batteryless operation removes the need for servicing or maintenance, so even the least accessible points can be fitted with the required equipment.

Get the Datasheet and Order Samples http://www.intersil.com

Low-Noise 24-bit Delta Sigma ADC ISL26132, ISL26134

Features

The ISL26132 and ISL26134 are complete analog front ends for high resolution measurement applications. These 24-bit Delta-Sigma Analog-to-Digital Converters include a very low-noise amplifier and are available as either two or four differential multiplexer inputs. The devices offer the same pinout as the ADS1232 and ADS1234 devices and are functionally compatible with these devices. The ISL26132 and ISL26134 offer improved noise performance at 10Sps and 80Sps conversion rates.

• Up to 21.6 Noise-free bits.

The on-chip low-noise programmable-gain amplifier provides gains of 1x/2x/64x/128x. The 128x gain setting provides an input range of ±9.766mVFS when using a 2.5V reference. The high input impedance allows direct connection of sensors such as load cell bridges to ensure the specified measurement accuracy without additional circuitry. The inputs accept signals 100mV outside the supply rails when the device is set for unity gain.

• On-chip temperature sensor (ISL26132)

• Low Noise Amplifier with Gains of 1x/2x/64x/128x • RMS noise: 10.2nV @ 10Sps (PGA = 128x) • Linearity Error: 0.0002% FS • Simultaneous rejection of 50Hz and 60Hz (@ 10Sps) • Two (ISL26132) or four (ISL26134) channel differential input multiplexer • Automatic clock source detection • Simple interface to read conversions • +5V Analog, +5 to +2.7V Digital Supplies • Pb-Free (RoHS Compliant) • TSSOP packages: ISL26132, 24 pin; ISL26134, 28 pin

Applications

The Delta-Sigma ADC features a third order modulator providing up to 21.6-bit noise-free performance.

• Weigh Scales

The device can be operated from an external clock source, crystal (4.9152MHz typical), or the on-chip oscillator.

• Temperature Monitors and Controls

The two channel ISL26132 is available in a 24 Ld TSSOP package and the four channel ISL26134 is available in a 28 Ld TSSOP package. Both are specified for operation over the automotive temperature range (-40°C to +105°C).

• Pressure Sensors

• Industrial Process Control

CAP

AVDD

DVDD

INTERNAL CLOCK

EXTERNAL OSCILLATOR

XTALIN/CLOCK XTALOUT

AIN1+ AIN1AIN2+ AIN2AIN3+ AIN3-

SDO/RDY INPUT MULTIPLEXER

PGA 1x/2x/64x/ 128x

ADC SCLK

ISL26134 Only AIN4+ AIN4PWDN

SPEED

A0

A1/TEMP AGND

GAIN0 GAIN1

CAP

DGND

VREF+

VREF-

DGND

DGND

NOTE for A1/TEMP pin: Functions as A1 on ISL26134; Functions as TEMP on ISL26132

FIGURE 1. BLOCK DIAGRAM

September 9, 2011 FN6954.1

Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2011 All Rights Reserved. All other trademarks mentioned are the property of their respective owners.

Improved Noise Figure TECHNICAL ARTICLE

TECHNICAL ARTICLE

Using an FDA and Input Transformer

Michael Steffes

Intersil - Sr. Applications Manager

Abstract: It is well known that combining a transformer with various types of amplifiers can improve the dynamic range. This works particularly well driving into the inverting side of either a differential dual op amp or a Fully Differential Amplifiers (FDAs). This approach has a number of subtle aspects exploiting the source impedance referred through the transformer to decrease the “Noise Gain” for those elements that get to the output by this gain. Those features, along with a detailed output noise analysis, simulation confirmation, and the resulting Noise Figure (NF) expressions, will be described here.

Differential Inverting Circuit Wideband Transformer Input

with

a

One of the lowest noise and distortion approaches to moderate frequency (<500Mhz) applications starts with the topology of Figure 1. In this example, a 4GHz Fully Differential Amplifier (FDA) is being used with an input 1:n step up transformer.

This approach is suitable for AC coupled signal paths where the source is coming from some known impedance (as in IF strips or other HF applications) and needs to be AC terminated over a broad bandwidth with that same impedance. The input transformer provides an amazing range of useful features in this circuit, including – 1. Converts single ended to differential if needed. If the source is already differential, as some SAW filters are,

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TECHNICAL ARTICLE

Figure 1: Differential Inverting FDA Design with an Input Transformer

they can be driven into the transformer differentially as well.

As the turns ratio increases, it is easy to see in table 1 that the useable flat bandwidth is compressing. As a practical matter, turns ratios from 1:1.41 to 1:3 are readily available for application to this approach. All of the devices in table 1 happen to offer a secondary centertap. Most of the time, it is preferable to leave that floating (DC and AC) in this application to avoid secondary imbalance issues from getting into the signal path and/or giving a DC path for the common mode current to flow.

-1dB Frequencies Turns Ratio Part Number Specified Ohms Centertap Fmin MHz

2. Since the 2 – Rg resistors feed into a differential virtual ground, they sum and input refer as a (2*Rg/n^2) input impedance at the transformer. To get a midband match, Rg is then completely constrained in this topology to be Rs*(n^2)/2 3. DC operating point isolation. Many designs operate single supply where the common mode control of an FDA like the ISL55210 sets the “Output” common mode.

Here, since there is no DC path for a common mode current to flow, the amplifier input pins will also be at the 1.2V internal default common mode shown in Figure 1.

4. From the voltage delivered at Vi, the transformer steps up the swing by the turns ratio and then that voltage gets to the output by the Rf/Rg ratio(Av). In this circuit, set the Rg resistors to get the match and then scale the gain to Av by adjusting the Rf resistors.

5. More interesting is the gain to the output for the FDA differential input noise. Since it sees both Rg and the source impedance reflected through the transformer as another Rg value on each side, that “Noise Gain” will be 1+Rf/(2Rg) or 1+Av/2. This circuit has the remarkable effect of giving more signal gain than “Noise Gain” when Av > 1/(n-0.5). For any particular target gain from Vi to Vo, this will normally improve the SNR. All of this comes at the cost of higher resistor noise and gain for the current noise terms at the input of the amplifier. Using this approach also needs to consider the bandwidth effects of the transformer, which limits

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Fmax MHz Manufacturer

1.41

ADT2-1T

50

Yes

1

200

MiniCircuits

1.41

TX-2-5-1

75

Yes

100

800

MiniCircuits

1.41

WBC2-1TL

50

Yes

0.4

260

Coilcraft

1.41

PWB-2-BL

50

Yes

0.264

200

Coilcraft

1.41

CX2045NL

75

Yes

3

300

Pulse Eng

1.41

ADT3-6T

50

Yes

0.2

250

MiniCircuits

ADT4-1WT

50

Yes

6

260

MiniCircuits

ADT4-1T

50

Yes

14

500

MiniCircuits

ADT4-6T

50

Yes

0.15

200

MiniCircuits

WBC4-1TL

50

Yes

0.5

380

Coilcraft

PWB-4-BL

50

Yes

0.272

356

Coilcraft

MABA-009600

50

Yes

1

300

Macom

CX2047NL

50

Yes

0.15

600

Pulse Eng MiniCircuits

ADT9-1T

50

Yes

2

150

WBC9-1T

50

Yes

0.58

261

Coilcraft

T16-1H

50

Yes

15

40

MiniCircuits

WBC16-1TL

50

Yes

1.2

157

Coilcraft

Table 1: Representative Wideband Transformers for Application in Figure 1

Figure 1 is showing an example using a very broadband, low noise device in this implementation. The Voltage Feedback Amplifier (VFA) ISL55210 (ref. 2) provides 4GHz of gain bandwidth product with only 0.85nV/√Hz differential input noise and 5pA/√Hz current noise on each input. It does this using only 35mA on a single 3.3V supply for 115mW power dissipation. The same basic design, however, can also be implemented with any of a wide range of Voltage Feedback Amplifiers (VFA) like the 1GHz ISL55190 as shown in Figure 2 (ref.3). This gives a huge range of supply and speed options to this basic circuit if the full universe of wideband VFA op amps can be used. And of course this circuit is particularly suitable to using duals.

Figure 2 is a simulation schematic implemented in a free, locally running, Spice simulation tool (ref.4). It

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TECHNICAL ARTICLE

the range of ‘turns’ ratios that might be applied. Table 1 shows some representative wideband transformers and their useable frequency range. These are pretty forgiving on the actual source and termination impedance. As those change from the expected or characterization values, the passband frequencies simply shift (ref.1).

TECHNICAL ARTICLE TECHNICAL ARTICLE

Figure 2: Dual Op Amp Version of the Inverting Transformer Coupled Circuit.

db @ VOUT / dB

16 15 14 13

20n

10n

20k

40k

100k

200k

400k

1M

2M

4M

10M

20M

40M

100M

Frequency / Hertz

Figure 4: Output Differential Spot Noise for Figure 2

Figure 4 shows a midband spot noise of 12.4nV with some peaking towards 100Mhz associated with the response shape of the ISL55190 inside this circuit. A noise gain of 4 is relatively low for this device so its response is actually peaking, which shows up more in the noise plot than the overall response plot. Input referred to the transformer input at this gain of 12 gets this output noise very close to 1nV at the input of the transformer including all terms.

Detailed noise calculations for the dual op amp circuit

12 11 10

This frequency response from the source in Figure 2, so a 6dB loss from the expected gain of 21.6dB and the AC coupling part of the response are shown in Figure 3. This is showing 0.5dB flatness from about 600kHz to 120Mhz. Output Noise / V/rtHz

offers an easy means to generate the typical results for both AC and output noise. In this example, a single 5V operation is assumed with a DC bias midpoint applied to the V inputs and the same basic signal path as an FDA implementation. The output is sensed through a dependent voltage source to convert differential to single ended to plot the differential output noise. The input transformer is a 1:2 turns ratio (RF transformers are normally specified in “ohms” ratios, so the “4” in the part number is the ohms ratio while the turns ratio is √4 = 2) terminated with the 2-100Ω gain resistors, then the amplifier signal gain is 6V/V giving it a total signal gain of 12V/V. Using a VFA takes advantage of the reduced “Noise Gain”. For the 1GHz Gain Bandwidth Product for the ISL55190, this NG=4 should give an F-3dB of 250Mhz in that stage while the WBC4-1TL should be relatively flat. Figure 3 shows the simulated frequency response while Figure 4 shows the output spot noise simulation.

200k

400k

1M

20M

4M

10M

20M

40M

Frequency / Hertz

Figure 3: AC Response for Figure 2

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100M 200M 400M

Each of the possible noise sources of Figure 2 can be placed into this circuit and combined to the output. One way to do this is to superimpose each voltage or current noise source, find its gain to the differential output voltage, then RSS those to get the combined output spot noise Visit www.eeweb.com

19

TECHNICAL ARTICLE 2

Total Target Gain

12

Required Av

6

Signal Gain =

n*Rf/Rg

value

12

Noise Gain

(1+Rf/(2*rG))

value

4

V/V

Rg value

(nˆ2)*Rs/2

value

100

ohm

Rf value

Rg * Av

value

600

ohm

value

50

ohm

Rs value Amplifier Eni

1.05E-09

V/√Hz

Amplifier In

5.50E-12

A/√Hx

V/V

Noise Source

Noise expression

Source Value

Gain

Rs resistor noise

√4kTRs

8.94E-10

6

Output Value Output Power

5.337E-09

2.88E-17

Rg resistor noise

√2*4kTRg

1.78885E-09

4

7.15542E-09

5.12E-17

Rf resistor noise

√2*4kTRf

4.38178E-09

1

4.38178E-09

1.92E-17

Eni noise

eni*√2

1.48E-09

4

5.94E-09

3.53E-17

In noise

in*√2

7.78E-12

600

4.67E-09

2.18E-17

Total output spot noise power

1.5626E-16

Total output spot noise voltage

1.25004E-08

Table 2: Detailed Output Spot Noise Calculation

to compare to the midband number in Figure 4. Table 2 steps through the noise calculation for this example.

Here each noise term gets generated then its gain to the output is used to get each terms’ spot noise contribution at the output in V/√Hz. Then, the noise power for each term is formed, summed, and then the square root of that is taken to estimate the combined spot noise at the output of Figure 2.

Looking at each voltage or current noise term at the bottom of this table – 1. The Rs noise is divided by 2 to the input then gained up – so it gets to the output with a gain of 6 2. There are 2- Rg resistors, so the spot noise is √2 of a single Rg noise – it gets to the output by the noise gain of 4.

3. There are 2-Rf resistors, so the spot noise is √2 of a single Rf noise – it gets to the output by gain of 1 4. There are 2 op amp Eni terms, so their combination is √2 of a single op amp – it gets to the output by the noise gain of 4 5. There are 2 inverting input current noise terms, so they get a √2 multiplier as well and then get to the output by the Rf resistor value.

this calculation slightly. First, there is only one differential input noise voltage so it does not get the √2 multiplier of the dual op amp design. More interesting is the current noise. There is always the question of whether the two current noise inputs might be correlated which changes the √2 adjustment in the table to something closer to a simple “2” value. For dual op amps, the real number is probably closer to √2 while for an FDA, where the inputs really are the two sides of a single differential input stage, something > √2 should be expected. Often, the measured noise is just slightly over this uncorrelated noise term model and that might be explained by this effect.

TECHNICAL ARTICLE

Total Differential Output Noise Calculations Dual Op Amp Implementation Target Turns Ratio

Converting this output differential noise to a Noise Figure Having the full output differential noise expression, including the contribution of the source noise from Rs, will allow the Noise Figure expression to be derived. There are many versions of the basic Noise Figure expression, but the simplest for the purpose here is given in Eq. 1.

e2i N F = 10Log(1 + ) kT Rs

The 2 terms inside the log expression are simply forming the ratio of the total output noise getting input referred by the gain (and this is including the Rs noise) ratio’ld against the noise delivered by the source resistance to the input. These are always done in noise powers, so that becomes noise voltages squared. Just dividing all the terms making up the output noise power by (nAv)^2 will generate the ei2 in Eq. 1. The kTRs is the noise power of the Rs resistor delivered to a matched load. So that spot noise voltage gets divided by 2 then squared to get the power (which is why the “4” in the “4kTRs” goes away).

Since all of the resistor terms in this design are determined by the source impedance, turns ratio, and then the target gain, the full Noise Figure expression will actually drop all of those out leaving just gain dependent terms, the turns ratio, and the amplifier noise terms. The full Noise Figure expression for the dual op amp design of Figure 2 is given in Eq. 2 (where here a=Av=Rf/Rg)

1

1

2

1

2

8 4 2 ∗ eni ∗ 2 + α + 2 ∗ (n ∗ ibi ∗ Rs ) Executing this calculation using the circuit values shown ) NF = 10 ∗ Log(3 + + 2 + predicts 12.5nV total differential output spot noise – very α α kT Rs close to the 12.4nV simulation value.

Going to the FDA implementation simply drops the 2 Going to the FDA implementation of Figure 1 will change from the voltage noise term to become Eq. 3 EEWeb | Electrical Engineering Community

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TECHNICAL ARTICLE Figure 5, will be giving about the same Noise Figure but a noise gain of 4.6.

2

2 Summary and Conclusions 8 4 2 ∗ eni ∗ 12 + α1 + 12 ∗ (n ∗ ibi ∗ Rs ) ) Teaming a broadband input step up transformer with a NF = 10 ∗ Log(3 + + 2 + α α kT Rs noise contribution while increasing the current noise contribution. Increasing the amplifier gain will decrease the Noise Figure monotonically. It is typical to solve for an optimum “n” for these equations. However, turns ratios are most easily available in specific steps as shown in Table 1. It might be more interesting to pick 4 different turns ratios and then sweep the amplifier gain achieving the same overall gain range in the analysis. For higher turns ratio’s, this means the amplifier gain span will be shifting down. That will be acting in the direction of increasing the Noise Figure, but will be giving wider bandwidth for any given amplifier. Continuing the ISL55190 example and generating the NF from Eq. 2 sweeping total gain from 4V/V to 40V/V (12dB to 32dB) gives the plot of Figure 5.

NF vs Gain (ISL55190) 12 11.5

Noise Figure (dB)

11 10.5

n=1.41

10

n=1.73

9.5

n=2

9

n=3

8.5 8 7.5 7

12

17

22

27

32

Gain in dB

Figure 5: Swept Gain Noise Figures with 4 Steps of Turns Ratios

Surprisingly, the net result of Eq. 2 gives about the same profile of noise figure vs. gain until the turns ratio gets to 3. This suggests that using the highest turns ratio consistent with the desired signal band and allowing the amplifier gain to go down might actually be desirable.

Operating with lower amplifier gain will also improve the loop gain for VFA based designs, possibly improving the harmonic distortion performance as well. For example, to get a 20dB gain, figure 5 would suggest using a turns ratio of 2 and an amplifier gain of 5 where the Noise Figure should be about 8.4dB. This Av = 5 will be a noise gain of 3.5 giving a bit more loop gain than say using a n=1.41 and then an amplifier gain of 7.1, which, according to

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differential inverting design can give an improvement in input referred noise. Using a VFA in the design will also be giving a lower “noise gain” than signal gain extending the amplifier closed loop bandwidth and increasing the loop gain. The dual op amp version can be applied using any of a wide range of dual, high performance op amps. The FDA version can actually give slightly lower noise but will be constrained by the narrower range of choices in implementation for this newer type of device.

Emerging high performance data acquisition platforms make good use of this technique and FDA’s to deliver very high dynamic range solutions showing excellent power efficiency (ref. 5).

References 1. Contact the author for a simple Spice Transformer modeling technique.

2. ISL55210, 4GHz, 0.85nV, FDA. http://www.intersil.com/ content/intersil/en/products/amplifiers-and-buffers/allamplifiers/amplifiers/ISL55210.html 3.ISL55190, Dual 1Ghz, 1.05nV Op Amp. http://www. intersil.com/content/intersil/en/products/amplifiers-andbuffers/all-amplifiers/amplifiers/ISL55190.html

4. iSim PE local simulation platform download (registration required). http://intersil.transim.com/ iSimPE.aspx

5. Ultra Low Power 8 to 14bit data acquisition platform. http://www.intersil.com/content/dam/Intersil/ documents/an17/an1725.pdf About the Author With 27 years of involvement in high speed amplifier design, applications, and marketing, Michael Steffes has introduced over 80 products spanning five companies while publishing more than 40 technical articles. His current focus is on high efficiency high speed ADC interfaces, DSL/PLC line interface solutions, and online design tool development. ■

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It is easy to see in these equations that increasing the turns ratio (n) will decrease the amplifier voltage

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