frankrose
Advanced Member level 3
Hi!
I want to use miller compensation in my OPAmp's 2nd stage. When I use miller capacitor only, the DC gain of the loop is 77dB, but when I use a series RC to shift the zero, the DC gain is decreasing to 68dB for different R values.
I don't understand why, a series RC shouldn't modify DC values. STB and AC analysis give the same results, the dominant pole is at 100Hz, I sample the loop gain at 0.1Hz. And I found that where the loop gain is smaller there the 1st stage has got a bit higher DC gain and the 2nd stage has got much lower DC gain. I attached a figure about the swept value of the R versus the DC gain. R is changing from 1Ohm to 25Ohm so basically it is just metal resistance.
I want to use miller compensation in my OPAmp's 2nd stage. When I use miller capacitor only, the DC gain of the loop is 77dB, but when I use a series RC to shift the zero, the DC gain is decreasing to 68dB for different R values.
I don't understand why, a series RC shouldn't modify DC values. STB and AC analysis give the same results, the dominant pole is at 100Hz, I sample the loop gain at 0.1Hz. And I found that where the loop gain is smaller there the 1st stage has got a bit higher DC gain and the 2nd stage has got much lower DC gain. I attached a figure about the swept value of the R versus the DC gain. R is changing from 1Ohm to 25Ohm so basically it is just metal resistance.