A Class-D amplifier architecture to compensate for the instability problem due to the LC filter variation

Master thesis (2022)

Authors

Z. Fu Electrical Engineering, Mathematics and Computer Science

Contributors

Q. Fan Microelectronics (supervisor 1)
H. Zhang Electronic Instrumentation - EEMCS (supervisor 2)
Faculty
Electrical Engineering, Mathematics and Computer Science
Copyright: © 2022 Zhuohui Fu
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Published Date

31-10-2022

Language

English

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Faculty

Electrical Engineering, Mathematics and Computer Science

Abstract

Class D audio amplifier is widely used in many electronic applications such as automobiles, laptops, and mobile phones. However, electromagnetic interference (EMI) generated by Class-D audio amplifiers frequently requires an external LC filter for suppression. The LC filter itself causes significant nonlinearity. Hence, feedback after LC is widely used to suppress this nonlinearity. Nevertheless, component tolerance in practical LC components causes instability problems in the feedback-after-LC Class-D amplifier. This thesis presents a class-D amplifier that suppresses LC filter nonlinearity by 40 dB at least and calibrates the variation of the cut-off frequency (f_LC) of the LC filter between 70kHz and 200kHz. This is implemented in a differential architecture, where the inner loop and outer loop ensure high in-band loop gain and stability, and the unity gain frequency is calibrated by a variable gain amplifier (VGA). This circuit is built in the 180-nm BCD process, achieving -108dB~-126dB total harmonic distortion (THD) after compensating for different LC cut-off frequencies.