Simplicity and low cost sustain the popularity of passive PWM DAC ripple filters despite their limitations. One of these limitations is a high output impedance caused by the series sum of filter ...

When used with other blocks and modules, a new approach to modeling operational-amplifier output impedance behavior can provide a more realistic overall behavioral model. Simulating the behavior ...

So, even bipolar amplifiers with “low” output impedance can have imperfect gain and linearity due to thermal feedback from the output transistors to the input stages.