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A High Efficiency 0.5W BTL Class-D Audio Amplifier with RWDM Technique Speaker: Dr. Simon C. Li

A High Efficiency 0.5W BTL Class-D Audio Amplifier with RWDM Technique Speaker: Dr. Simon C. Li Thanks ! Session Chairman. Good morning, everyone. My name is (I am) Simon Li. As a master student on behalf of ATIS Lab., electrical engineering department, National University of Tainan, Taiwan. Here is our topic for oral presentation.

OUTLINE 1. Introduction 2. Principle of RWDM Technique 3. Circuit Design 4. Experimental Results 5. Summary

Five sections is in the outline. 1. We start/begin with Introduction from brief history of Topic (Early work and Challenges) 2. A concise review about Principle of RWDM Technique is described. 3. Several aspects relating to Circuit Design are considered and discussed. 4.Then our proposed circuit is verified by Experimental Results which will be discussed. 5. Finally, a Summary of our work is concluded.

Renewed interests in class-D integrated audio amplifiers Especially for portable and consumer electronics: (1) Hearing-aids, (2) Multimedia players, (3) Notebook computers, (4) USB hub-powered/wireless speakers, (5) Automotive audio amplifiers, etc. 1. Introduction

Renewed interests in class-D integrated audio amplifiers Especially for portable and consumer electronics: (1) Hearing-aids, (2) Multimedia players, (3) Notebook computers, (4) USB hub-powered/wireless speakers, (5) Automotive audio amplifiers, etc. 1.Introduction Function/Significance ( 功能性 / 重要性 ) Field/Area ( 應用領域 )

Amplifier Classes Amplifier Type Output Transistors Advantages Disadvantages Comments ALinear Always Conducting [ I b > I o(max) ] Sound the Best; Most Linear; Lowest Distortion Most Inefficient (~20%) ; Large/Hot/Heavy Only 10% “high-end” market BLinear Each device On /only half cycle [ I b(idle) =0] Efficiency > A Crossover : Poor linearity & Distortion No audio 2-way radio only CLinear Each device On < half cycle [ Pulsed On] Efficiency = B Large P o Distortion No audio RF Tx broadcast ABLinear Mid- Conduction [ I b = C o ] [ Barely On] Sound = A Good Efficiency Large P o Heat ~50% Power Heat Sink Dominate audio market D Switching Gate-Drive Fully on/off P = I V = 0 Best Efficiency ( ~ 90%) N0 Heat Sink Small Optimized THD PW/   modulation Advanced Technology & Integrated Systems Laboratory ATIS Lab.

– The reduction of supply current required which translate to longer run-time on batteries – The reduction of heat generated that translates to more output power in a smaller package, and elimination of heat sinks Class-D amplifier provides two main advantages over the class A/AB amplifiers.

(a) PWM Scheme (Fixed Switching Frequency) Two Analog Schemes in Class-D Amplifier

(b) RWDM Scheme (Varied Switching Frequency) Two Analog Schemes in Class-D Amplifier

2. Principle of RWDM Technique From the modulator-operating principles,  RWDM output signal is decided by the integrator in the feedback path.

Modulator Switching Frequency f s A maximum value (S c /4∆V ) at  t = k (π/2), k is odd  an inherent minimum pulse width So no needed to ensure minimum pulse width duration

Modulator Switching Frequency f s A minimum value (S c /4∆V)[1-(  V i /S c ) 2 ]at  t = k (π/2), k is even  an inherent minimum value of maximum pulse width

Average Switching Frequency f ave Averaging the modulator instantaneous switching frequency over several cycles of the audio input signal 

Architecture of RWDM Class-D Amplifier

Principle of RWDM Technique

3. Circuit Design Bridge Tied Load (BTL) RWDM Class-D Amplifier

A Rail-to-Rail Floating–Gate Hysteresis Comparator

Simulated Output Voltage Signal ( Input Audio Sinusoidal Waveform of 1 V, 20 kHz)

RWDM Output Signal ( Input Audio Sinusoidal Waveform of 1 V, 20 kHz)

4. Experimental Results Measured Output Voltage Signal with Input Audio Waveform of 1 V, 10 kHz

Frequency Response (Magnitude/Phase)

Efficiency vs. Audio Signal Amplitude

A Microphotograph of 0.5W RWDM Class-D Amplifier IC

Table I Summary of RWDM Class-D IC Major Specs Class-D Audio IC SpecificationsCurrent Art Power Supply3V Speaker Load8-Ω Gain6dB RWDM Switching Frequency> 200 kHz Static Power Dissipation68.6 μW Max Output Swing5.4 V Max Output Power /Channel0.5 W THD+N (1 kHz)< 1.6% Efficiency91~96% SNR75dB PSRR-90 dB

5. Summary  The power efficiency of this amplifier is 91~96% at 0.5 Watts per channel with a 3V power supply. Watts per channel with a 3V power supply.  By virtue of the high efficiency of Class-D architecture coupled with the low voltage operation provided by the use of floating-gate CMOS hysteresis comparator, this amplifier is suitable for portable devices with battery operations. coupled with the low voltage operation provided by the use of floating-gate CMOS hysteresis comparator, this amplifier is suitable for portable devices with battery operations.

Table I Summary of RWDM Class-D IC Major Specs Class-D Audio IC SpecificationsCurrent Art Power Supply3V Speaker Load8-Ω Gain6dB RWDM Switching Frequency> 200 kHz Static Power Dissipation68.6 μW Max Output Swing5.4 V Max Output Power /Channel0.5 W THD+N (1 kHz)< 1.6% Efficiency91~96% SNR75dB PSRR-90 dB