Low cost implementation of filterless class D audio amplifier with constant switching frequency

Pyung Choi is with the School of Electrical Engineering and Computer Science, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu, South Korea (e-mail: p0choi@ee.knu.ac.kr)
class D audio amplifier is proposed in this paper. The
proposed Filterless class D audio amplifier provides the
advantages of both low total system cost and generation of
VCMP+
Class D Power stage
VPWM+
CHY
VHY+
RHY2 RHY2
RHY1 RSYNC
RHY1
VHY-
Speak
Index Terms —variable hysteresis controller, class D amplifier, constant switching.
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Fig. 2. Zoom-in schematic of hysteresis window and example of comparator outputs.
the form of high efficiency. As the traditional class D audio
amplifier employs pulse-width modulation for amplification of To resolve the switching frequency variation of the self-
generator for filter free class D amplifier, a self oscillation
To reduce the total system cost, a self-oscillating class D hysteresis controller with constant switching frequency was
In another attempt to reduce system cost, a filter free class implementation.
D amplifier was presented in 2004, which generated a 3-level
PWM output to eliminate low pass filter using a double-sided
amplifier based on hysteresis control is very desirable due to In this paper, a new and simple configuration of the
the high linearity. However, the class D amplifier based on filterless class D audio amplifier using variable hysteresis
general class D power stages. The dashed lined block shown in Fig.1 is the hysteresis control circuit to make the variable hysteresis window keep a close constant switching frequency. Simultaneously, it also fulfills the synchronization function for generating 3-level PWM output to eliminate final low pass filter.
The proposed class D amplifier is based on a continuous sigma-delta modulation with the hysteresis window [1]. The main difference from other constant switching class D amplifier with a hysteresis controller is that the proposed class D amplifier produces the hysteresis window through the
Fig.1 shows the schematic diagram of the proposed filterless class D audio amplifier with variable hysteresis controller. The proposed class D amplifier consists of integrators, comparators, a variable hysteresis controller and
amplifier based on hysteresis control was introduced to introduced in 2005 [3]. Though it could resolve the
remove the external carrier signal, achieve a simpler system synchronization for 3-level PWM output and switching
Contributed Paper Manuscript received October 15, 2006
0098 3063/06/$20.00 © 2006 IEEE
H.-S. Kim et al.: Low Cost Implementation of Filterless Class D Audio Amplifier with Constant Switching Frequency
Jang-Kyoo Shin is with the School of Electrical Engineering and Computer Science, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu, South Korea (e-mail:jkshin@ee.knu.ac.kr)
CHY
Integrator RIN
பைடு நூலகம்
VCMP-
Class D Power stage
VPWM-
-1
Comparator
CI
I. INTRODUCTION
RF
Of late, the use of switch mode or class D amplifier is Fig. 1. The proposed filterless class D audio amplifier with variable increasing in audio applications because of the advantage in hysteresis controller
configuration, and lower the total system cost [1]-[2]. frequency variation, it also needed additional low pass filters
Moreover, using in audio amplifier applications, the class D and comparators.
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IEEE Transactions on Consumer Electronics, Vol. 52, No. 4, NOVEMBER 2006
Low Cost Implementation of Filterless Class D Audio Amplifier with Constant Switching Frequency
II. VARIABLE HYSTERESIS CONTROLLER
natural sampling PWM [4]. Although it succeeded to eliminate the low pass filter as a demodulator using a 3-level PWM output, it still remained needs for additional circuit to generate carrier signal.
audio input signal, the total system cost has remained higher oscillating class D amplifier and the elimination of carrier
than the traditional class AB amplifier.
synchronized 3-level pulse-width modulated (PWM) output.
Moreover, as a result of hysteresis window variation, a close
to constant switching frequency of PWM output is obtained.
1 Hyoung-Sik Kim is with the School of Electrical Engineering and Computer Science, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu, South Korea (e-mail: eehskim@ee.knu.ac.kr)