Answer 8—Op-amps generally have a minimum of 12 dB/octave slope in their gain curves as they approach their high-frequency limit of operation. This means that the phase shift in the amplifier itself is asymptotically approaching 180° at high frequencies. In advanced designs, there can be a third pole in the frequency response that pushes the phase shift toward 270°, and this means that it can easily reach 180° before the gain has dropped below unity. If such an amplifier isn’t specifically compensated for this, it won’t be inherently stable in a unity-gain configuration, where the negative feedback is 100%.

Contributor: David Tweed