Single Ended Class D Switching Amplifier using CMOS Technology

GRD Journals- Global Research and Development Journal for Engineering | Volume 5 | Issue 11 | October 2020 ISSN- 2455-5703

Single Ended Class D Switching Amplifier using CMOS Technology S. Selva Nidhyanandhan Associate Professor Department of Electronics and Communication Engineering Mepco Schlenk Engineering College, India

Saranya Devi V PG Scholar Department of Electronics and Communication Engineering Mepco Schlenk Engineering College, India

Abstract In previous research, the design of Class E Amplifier designed using Silicon Germanium Infineon BFQ790 BJT Transistor as the switching component. And it will be improving the technology to be applied on IOT (Internet of Things) transceiver with 2.4 GHz frequency hence the new research is taken. Hence in this modern world, the main goal of audio amplification in an audio system is to accurately reproduce and amplify the given input signal. And one of the biggest challenges is to have high output power with least amount of power loss as possible. Class D amplifier technology is making an increasing impact on the live sound world by offering high power with zero power dissipation and less weight than ever before. Now-a-days, portable music devices are becoming more popular with a growing demand of external sounds in portable music devices. This paper proposes a design of class D single ended switching power amplifier using BF554 BJT Transistor by CMOS technology at frequency below 2.4 GHz. The simulation from ADS (Advanced Design Systems) software shows that the amplifier gain is 4.326 dB at frequency 2 GHz. Finally this design ensures the stability factor of the class D amplifier 2.410 which is unconditionally stable.

Keywords- Power Amplifier, ADS, BF554BJT, CMOS, Silicon Germanium Infineon BFQ790BJT

I. INTRODUCTION Most of the electronic systems require at least one stage of amplification. Hence amplifiers can be seen in almost all the electronic devices. Amplifiers are the devices that increase the amplitude of the input signal. The output of the power supply is modulated by the Amplifier. Amplifiers increase only the amplitude and the other parameters such as frequency and shape remain constant. There are many types of amplifiers available. But they can be distinguished by the type of signal they amplify.

Power amplifier is an electronic device which provides sufficient power to an output load to drive a speaker or other power device typically a few watts to ten watts. It is used to increase the power i.e. the product of output voltage and current is greater than the product of input voltage and current.

The Class D amplifier is one of many classes of amplifier. Some other amplifier designs, like Class A, Class B, and Class AB are widely used because of their simplicity and ease of use in almost any application. Class D amplifiers have historically only been used in a limited number of applications like motor control, because it is more difficult to generate the high quality signals required for audio applications with a Class D amplifier.

Recently, however, Class D technology has advanced sufficiently to allow these amplifiers to accurately and cleanly amplify audio signals. Class D having increased power efficiencies compared to other classes of power amplifier and to reduce noise filter is added after the amplifying stage. Since the filter only needs to attenuate signals above the audible frequencies, it is not essential that the filter be extremely precise. It may be therefore realized by a fairly simple, low-pass, passive filter.

In BJT amplifies the signal by operating in the linear region. This allows the output voltage to vary based upon the principle that the current flowing between the collector and the emitter of the transistor is proportional to that flowing between the base and the emitter. As a result, the high power output signal follows the input signal very accurately, reducing noise and distortion. The linear region of the transistor, however, is very inefficient. It constantly drains energy from the power supply, even if the input is grounded and there is no signal to amplifier.

Fig. 1: Block Diagram of Class D audio Amplifier

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Single Ended Class D Switching Amplifier using CMOS Technology (GRDJE/ Volume 5 / Issue 11 / 003)

According to the working principles, class D amplifier design is divided into three stages i.e., comparator, amplifier, low pass filter.

[1] Dessy Oktani, Basuki R Alam et al. brings the new design of the class E power amplifier using Silicon Germanium Infineon BFQ790 BJT Transistor as the switching component. The authors uses output voltage of this amplifier is 0.84 volt, Voltage Gain 20 dB and power gain S(2,1) is 5.968 dB. Wei Lu, Yun Yin, Liang Xiong , Tong Li, Hongtao Xu et al. [2] proposed a nonlinear analytical model for an inverter-based switched-capacitor Class-D RF power amplifier (SCDPA). The root causes of the SCDPA AMAM and AMPM nonlinearities are analyzed. The major factors affecting SCDPA nonlinearities are identified as the unequal on-resistances of selected cell and unselected cell. The results compared on both transistor level and system level. The analysis of amplitude is more complicated. The waveform obtain bumped during steady state brings much impact on the amplitude. [6]Hyoungsoo Kim, Ockgoo Lee, Kwan-Woo Kim, Franklin Bien, Kyutae Lim, Chang-Ho Lee ,Joy Laskar et al. proposed a non-isolated multilevel linear amplifier with nonlinear component (LINC) power amplifier (PA) implemented in a standard 0.18-Οm complementary metal–oxide– semiconductor process. Using a nonisolated power combiner, the overall power efficiency is increased by reducing the wasted power at the combined out-phased signal. However, the efficiency at lowpower still needs to be improved. [7]Haifeng Ma, Ronan van der Zee and Bram Nauta used the power dissipation analysis and the design of an efficiency-improved high-voltage class-D power amplifier. Implemented in 0.14 micrometer BCD process, the amplifier achieves 93% efficiency at 45 W output power,>80% power efficiency down to 4.5 W output power and>49% efficiency down to 0.45W output power. The dynamic power stage activation is not suitable for highvoltage applications because the parasitic capacitance at the output node of the power stage is still present for the inactive part of the power stage, resulting in the same high switching loss.

Although the above proposed methods of using different classes of amplifiers brings constant innovations in semiconductor technologies. And increasing the use of Class D amplifiers brings improvements in higher efficiency, increased power density and better audio performance. Hence, compared with the state-of-the-art modeling approaches, these works provides a more complete nonlinear model to enable fast architecture study and quick circuit-level designs.

II. APPLYING CLASS D TO AUDIO DESIGN High power efficiency, combined with a compact and lightweight design, distinguishes Class D amplifiers from other amplification techniques. Power efficiency is becoming very important, as concerns regarding power usage increase. A tangible benefit of reduced power consumption is that it becomes less expensive to use the amplifier. While this may not be a major concern for homeowners, in the live audio market power is sometimes generated on site, especially for large concerts, and larger generators are more expensive to use. From a marketing standpoint, the compact and lightweight design made possible by high efficiency is attractive to all users. Home audio systems can be designed to be hidden away, helping to reduce clutter in a room.

In the touring market, smaller amplifiers mean lower shipping costs and a reduction in labor when setting up before and packing up after a concert.

III. DESIGN METHODOLOGY Class D amplifier is employed by using BF554 BJT Transistor as the switching component at 2 GHz. Hence a low pass filter is designed first is to get the S-Parameter values. Then design of this low pass filter is analysed to check insertion and isolation losses. Finally a transistor is designed using BF554 BJT Transistor as the switching component at 2 GHz to check the stability of the amplifier. The stability analysis where done using the ADS software simulation hence the amplifier is unconditionally stable which is 2.4.

Fig. 2: Block diagram of Cass D design methodology

A typical Class D power amplifier consists of a sawtooth waveform generator, comparator (based on an OPAMP), switching circuit, and a low pass filter.

A. Comparator The main job of the comparator is to digitize the input audio signal by mixing it with the chopping saw tooth waveform. The result of this mixing will be a digital copy of the analog input signal. The low frequency components of the digital signal will

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Single Ended Class D Switching Amplifier using CMOS Technology (GRDJE/ Volume 5 / Issue 11 / 003)

represent the input audio signal and the high frequency components of the digital signal are of no interest.Even though the output of the comparator is a digital representation of the input audio signal, it doesn’t have the power to drive the load (speaker). The task of the switching circuit is to provide enough current and voltage gain which is essential for an amplifier. The switching circuit is generally designed around MOSFETs. B. Sawtooth Waveform Generator The saw tooth waveform generator generates a high frequency sawtooth waveform for sampling the input audio signal. The frequency of the saw tooth waveform is usually selected 10 times the maximum frequency of interest in the input audio signal.

C. Low Pass Filter The task of the low pass filter is to filter out useful low frequency components from the output of the switching circuit. The output of the low pass filter will be a scaled replica of the input audio signal. Negative feedback loops are often included in between the low pass filter output and the comparators audio input in order to fight the errors.

Fig. 3: Low Pass Filter Design for Class D Power amplifier

Fig. 4: Simulation of LPF

In figure 4 the S-Parameter values are obtained which will be useful for the class D amplifier design and to check the stability of an amplifier.

FREQUENCY 2GHz

Table 1: S-Parameter at 2 GHz S(1,1) S(1,2) S(2,1) -12.722 -26.258 -26.258 <161.485 <-16.125 <-16.125

S(2,2) -12.722 <161.485

Harmonic balance is a frequency-domain analysis technique for simulating nonlinear circuits. High Total Harmonic Distortion (THD) is indicative of high noise levels, which detect significantly from the audio quality of the output. Advances in

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Single Ended Class D Switching Amplifier using CMOS Technology (GRDJE/ Volume 5 / Issue 11 / 003)

technology have allowed for faster modulation techniques, however, which can reduce THD to fractions of a percentage in Class D audio amplifier. Here, order[1]=3 describes the number of orders for harmonic balance having Freq[1]=2GHz.

Fig. 5: Harmonic Balance

Fig. 6: Simulation Output for Harmonic Balance

From figure 6 the harmonic balance simulation output will be obtained using ADS software which shows the output voltage for 3 number of orders in dbm.

IV. RESULTS AND DISCUSSION This section describes the results of Power amplifier characteristics and the transistor circuit for class D amplifier.

Table 2: Power amplifier Specification PARAMETER SPECIFICATION Frequency 2 GHz Gain >6 db Output Power 5 watts

Recent advancements in Class D modulation techniques have allowed Class D amplifiers to flourish in applications where a linear amplifier is dominated. Modern Class D amplifiers include all of the advantages of Class AB amplifiers (i.e., good linearity and minimal board-space requirements) with the added bonus of high power efficiency. Currently, there are a wide variety of Class D amplifiers available, thus making them suitable for numerous applications. These applications range from low-power portable applications (e.g., cell phones, notebooks) in which battery life, board-space requirements, and EMI compliance are of atmost importance, to high-power applications (e.g., automotive sound systems or flat-panel displays) where minimizing heat sinking requirements. Having a fundamental understanding of Class D amplifiers and their recent technological advances will aid designers in selecting the correct amplifier for their application and allow them to successfully weigh the advantages and disadvantages of specific features.

GAIN (db) =VOUT VIN By using the above equation, the simulated output result for the transistor circuit as figure 9 for class E amplifier is obtained with the gain 4.326 db with the stability factor K= 2.410 as figure 10 which is unconditionally stable.

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Single Ended Class D Switching Amplifier using CMOS Technology (GRDJE/ Volume 5 / Issue 11 / 003)

Fig. 7: Power amplifier characteristics circuit for Class D Amplifier

Fig. 8: Transistor circuit for Class D Power Amplifier

Fig. 9: Simulation Output

Fig. 10: Stability Analysis

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Single Ended Class D Switching Amplifier using CMOS Technology (GRDJE/ Volume 5 / Issue 11 / 003)

Table 3: Stability Condition CONDITION Stability Factor Conditionally Stable K<1 Unconditionally Stable K>=1 Table 4: Stability output for Class D Amplifier FREQUENCY STABILITY 2GHz 2.410

V. CONCLUSION A design of class D single ended switching power amplifier design using BF554 BJT Transistor by CMOS technology at frequency below 2.4 GHz. From the above design, it can be concluded that the class D amplifier design using BF554 BJT Transistor gives the stability analysis which is unconditionally stable with the stability factor 2.410 as figure 10. And by using the simulation from ADS (Advanced Design Systems) software shows that the output of the amplifier gain as 4.326 db as shown in figure 9 which will be greater than 1 db at frequency 2 GHz.

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Dessy Oktani, Basuki R Alam “Design of Switching Power Amplifier 2.4GHz”, IEEE Conference, 2018 Wei Lu, Yun Yin, Liang Xiong , Tong Li, Hongtao Xu “Nonlinear Analytical Model for Switched-Capacitor Class-D RF Power Amplifiers”, IEEE transactions on Circuits And Systems–I: Regular Papers, Vol. 66, No. 6 ,2019 Xudong Wang, Zhengming Zhao, Kai Li, Kainan Chen, Fang Liu “Analysis of the Steady State Current Ripple in Multileg Class-D Power Amplifiers Under Inductance Mismatches “, IEEE Transactions On Power Electronics, Vol. 34, No.4, April 2019.

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Haifeng Ma, Ronan van der Zee, and Bram Nauta “A High-Voltage Class-DPower Amplifier With Switching Frequency Regulation for Improved High Efficiency Output Power Range “IEEE Journal Of Solid-State Circuits, Vol. 50,No 6, June 2015.

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