A Chopper Class-D Amplifier for PSRR Improvement Over the Entire Audio Band

Huajun Zhang, Nuriel N.M. Rozsa, Marco Berkhout, Qinwen Fan*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

The power supply rejection ratio (PSRR) of conventional differential closed-loop Class-D amplifiers is limited by the feedback and input resistor mismatch and finite common-mode rejection ratio (CMRR) of the operational transconductance amplifier (OTA) in the first integrator. This article presents a 14.4-V Class-D amplifier employing chopping to tackle the mismatch, thereby improving the PSRR. However, chopping-induced intermodulation (IM) within a pulsewidth modulation (PWM)-based Class-D amplifier can severely degrade PSRR and linearity. Techniques to mitigate such IM are proposed and analyzed. To chop the 14.4-V PWM output signal, a high-voltage (HV) chopper employing double-diffused MOS (DMOS) transistors is developed. Its timing is carefully aligned with that of the low-voltage (LV) choppers to avoid further linearity degradation. The prototype, fabricated in a 180-nm BCD process, achieves a PSRR of >110 dB at low frequencies, which remains above 79 dB up to 20 kHz. It achieves a total harmonic distortion (THD) of -109.1 dB and can deliver a maximum of 14 W into an 8-Ω load with 93% efficiency while occupying a silicon area of 5 mm².

Original languageEnglish
Article number9745547
JournalIEEE Journal of Solid-State Circuits
DOIs
Publication statusAccepted/In press - 2022

Keywords

  • Audio power amplifier
  • Class-D amplifier
  • intermodulation (IM)
  • power supply rejection ratio (PSRR)
  • total harmonic distortion (THD).

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