Abstract-A frequency compensation technique for MOS audio power amplifiers is presented that allows the frequency compensation capacitors around the power transistors to be smaller than the circuit parasitics without power or stability penalty. Stability is analysed by inspecting the output impedance of the closed loop amplifier, instead of the traditional open-loop gain. By degenerating the gain of the penultimate stage, the output impedance is shaped such that the stability of the audio amplifier is guaranteed for complex loudspeaker loads. The realized amplifier features a THD of 0.005% @ (1 kHz, 10 W), an SNR of 110 dB(A), and stable operation for any passive load up to 50 nF.
A 4x45W (EIAJ) monolithic car audio power amplifier is presented that achieves a power dissipation decrease of nearly 2x over standard class AB operation by sharing load currents between loudspeakers. Output signals are conditioned using a common-mode control loop to allow switch placement between loads with minimal THD increase. A prototype is realized in a SOI bipolar-CMOS-DMOS process with 0.5µm feature size. Die area is 7.5x4.6mm 2 . THD+N @(1kHz,10W) is 0.05%.
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