A 121.4-dB DR Capacitively Coupled Chopper Class-D Audio Amplifier

Abstract

This article presents a class-D amplifier (CDA) with high dynamic range (DR). To eliminate the typically dominant noise contribution of a resistive feedback network, the input and feedback signals are chopped and applied to a capacitive feedback network. However, this leads to high-voltage (HV) transients at the input of the loop filter, which, due to timing and impedance mismatch in the chopped feedback network, could degrade linearity and even overstress low-voltage (LV) core devices. Robust processing of the HV chopped feedback signal is guaranteed with chopper timing skew correction, chopper impedance matching, and deadbanding. The prototype, implemented in a 180-nm bipolar-CMOS-DMOS (BCD) process, achieves 121.4 dB of DR, 5.9 dB higher than state-of-the-art closed-loop CDAs, and 8-μVRMS output-referred noise (A-weighted). It also achieves a peak total harmonic distortion (THD) + N of -109.8 dB and a peak efficiency of 93%/88% while driving 15 W/26 W into an 8-4-Ω load.