ABSTRACT
Almost all audio power amplifi ers use dominant-pole compensation. A “pole” here is a frequency from which
the open-loop gain falls of at 6 dB/octave; when a second pole at a higher frequency comes into action, the gain falls off at 12 dB/octave. To implement dominant-pole compensation, you take the lowest frequency pole that exists and make it dominant; in other words so much lower in frequency than the next pole up that the total loop-gain (i.e., the open-loop gain as reduced by the attenuation in the feedback network) falls below unity before enough phase-shift builds up to cause HF oscillation. With a single pole, the gain must fall at 6 dB/ octave, corresponding to a constant 90° phase shift. Thus the phase margin, the difference between the actual phase shift and the 180° that will cause oscillation is 90°, which gives good stability.
