I am trying to design an op-amp with a high-pass feedback. The diagram is shown below. The high pass feedback has a corner frequency at 1Hz.
The op-amp itself is two stage as can be seen below.
Based on the books that I have been reading and the number of designs I have found online, the procedure that is generally used involves taking the compensation capacitor into account from the get go. In all of those designs, we assume we want a phase margin > 62 degrees and come up with a value for the compensation capacitor. My question is, how would a high-pass filter in the negative feedback path affect the choice of compensation capacitance needed? In all the designs I've seen, the compensation capacitance was taken to be 0.22*CL (0.22 to meet the phase margin requirements). Should the addition of a high pass filter affect this calculation and if so, how ?
Here is the other question: I have only about 55𝜇A to play with based on the power requirements. In other to meet the required GBW, I need about 17𝜇A in the branch that contains M1 and M3. I would naturally just mirror this current to the branch containing M2 and M4. However, this would the current in this branch 34𝜇A leaving only about 20𝜇A for the second branch which is too little. The second branch should consume the highest amount of current. The only way I can reduce the current in the middle branch is by mirroring only a fraction of 17𝜇A into the branch containing M2 and M4. This makes things very hard because it would implying that M1 and M2 (and also M3 and M4) are no longer of the same sizes. Based on the number of designs I've seen, M1 and M2 (and also M3 and M4) are always of the same sizes. This seems to imply that something is quite wrong. I wouldn't mind some assistance if possible.