min wrote on Feb 21st, 2008, 10:17pm:Hi ,
Thanks for your advices, and I have change the circuit and the phase margin = 70 degree and dc gain = 82dB
and I have another question :
1. I simulate the ota total input referred noise is 8uV and I want to decrease this number. I increase the input differential pair M1 M2 gm and the noise will decrease , but I don't know why , what is the reason ? and is there any other method to reduce the inpt referred noise ?
2. Is the resistor in circuit lower the noise of avdd or lower noise of mosfet M3 & M4?
I see the main noise source is the input differential pair M1 M2.
Min
2- the resistors decrease the gm of M3 and M4 and hence decrease their contribution yet adding resistance will add some more noise (thermal noise)
also those resistors help in PSR+ as they increase the resistance between the output and Vdd
beside headroom issues when using resistors