A low-distortion output stage with improved stability for monolithic power amplifiers

Abstract

A low-distortion class AB output stage with improved stability suitable for monolithic power amplifiers (P/sub 0/>or=40 W) is described. The concept has been verified on a 12-W breadboard version as well as on a partly integrated prototype, and is supported by computer simulations for P/sub 0/>or=40 W A biasing control law which guarantees predictable conduction of both output transistors at all times is implemented. This reduces crossover distortion and allows the customary quasi-p-n-p compound transistor to be eliminated, thus also improving stability. Linearity is improved by use of local negative feedback. Phase margin is improved by application of high-frequency feedforward. Measured phase margin is around 60 degrees and total harmonic distortion for a load of 7 Omega is about -80 dB at 20 kHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>