ABSTRACT
This chapter deals with the extensive subject of compensation for stability, to showcase a complete 50W/8Ω power amplifier, and demonstrate the distortion performance of that amplifier with various compensation schemes. Nested feedback is a way to apply more negative feedback (NFB) around the output stage without increasing the global feedback factor. The output has an extra voltage gain stage bolted on, and a local feedback loop is closed around these two stages. This NFB around the composite block reduces output stage distortion and increases frequency response, to make it safe to include in the global NFB loop. The Voltage Amplifier Stage (VAS) is enhanced by an emitter follower inside the Miller compensation loop, so that the local NFB which linearises the VAS is increased by augmenting total VAS beta, rather than by increasing the collector impedance by cascoding. The extra local NFB effectively eliminates VAS nonlinearity.
