Objective of compensation is to achieve stable operation when negative feedback is applied around the op amp. Miller - Use of a capacitor feeding back around a high-gain, inverting stage. Miller capacitor only Miller capacitor with an unity-gain buffer to block the forward path through the compensation capacitor. Can eliminate the RHP zero.
It is observed that as the size of the compensation capacitor is increased, the low-frequency pole location ω1 decreases in frequency, and the high-frequency pole ω2 increases in frequency. The poles appear to “split” in frequency.
Input capacitance is easily compensated by adding a feedback capacitor into the circuit. The value of the feedback capacitor should be just large enough to achieve the desired overshoot response, because larger values cause a loss of high-frequency performance. 1. Ron Mancini, Op Amps For Everyone (Newnes Publishers, 2003).
The DC gain in Equation 2 remains the same as it was without an input capacitor, but the pole is added at f = 1/(2 πR F||R GCIN). If this pole occurs at approximately 3 MHz, it reduces the gain by 3 dB and adds a 45o phase shift at that frequency. Using C IN = 20 pF and RG||R = 2.7 k
In addition, a better understanding of the internals of the op amp is achieved. The minor-loop feedback path created by the compensation capacitor (or the compensation network) allows the frequency response of the op-amp transfer function to be easily shaped.
Equation 1 The quantity CM in Equation 1 is referred to as the Miller capacitance and is calculated as follows C M = (1 + av)C C M = (1 + a v) C Equation 2. The Miller capacitance In words, the feedback capacitance C reflected to the input, gets multiplied by 1 + av.