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Understanding Op-Amp frequency compensation is extremely important for anyone working with op-amps, an uncompensated op-amp it very likely to oscillate as the point of unity gain is often well past the point at which the phase shift reaches 180 degrees, following the Barkhausen criterion this results in oscillation.
An uncompensated op-amp has a single pole which is set by the limitations of the design and semiconductors, which in the circuit is represented by the 300 pF capacitor, oscillation can be prevented by one of two ways, increasing gain which shifts the frequency response down resulting in unity gain occurring at a lower frequency or by compensation which inserts a pole at a lower frequency.
Most op-amps available are internally compensated so when used within their design specifications they are stable, this is represented by the 20 nF capacitor giving the classic S curve frequency response, however even internally compensated op-amps can become unstable when driving a capacitive load such as the gate of a MOSFET or even the input of another op-amp, thus requiring external compensation.
External compensation can be achieved by various means but the easiest is just to insert another pole, this can be done with the 1 pF capacitor in the circuit, this of course reduces bandwidth and slew rate but also reduces ringing and prevents oscillation if a sufficient value is chosen.
This is rather difficult to represent in EC due to the very simple op-amp model, so I suggest using the free LTspice if you want to experiment, in many cases where gains greater than 1 are used additional compensation is unnecessary but in cases where oscillation or significant ringing occur you then need to think about compensation.
There is a good read on the subject available at: www.ti.com/lit/ml/sloa079/sloa079.pdf
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