Feedforward compensation of the amplifier output stage for improved stability with capacitive loads

It is pointed out that the stability margin of an audio power amplifier is reduced by a pole in the loop-gain transfer function caused by shunt capacitance in the loudspeaker load. The problem is most severe in amplifiers with output stages that have a high output impedance before feedback. Because MOSFET devices can have an output impedance that is much higher than BJT (bipolar junction transistor) devices, amplifiers with MOSFET output stages are particularly susceptible to load-induced oscillations. A feedforward frequency compensation technique is described that bypasses the pole in the output stage caused by the load capacitance for improved stability of the amplifier.<
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