Hello everyone.........

I am working on Sigma Delta Modulator For AUDIO Range of freq.....ie 0 to 20KHz.....
I designed the two stage class A/AB amplifier, internal positive feedback hysteresis comparator and 1 bit DAC....

My supply voltages are 0 to 1.8V in 180nm of technology in CADENCE....
But for both amplifier and comparator my PSD vs Freq graph is not comming properly.....The higher harmonics (4th, 5th ,etc) are not suppressing.....
I am attaching the PSD vs Freq graph of both amplifier and comparator...please go through it...
Along with this Iam attaching amplifier and comparator schmetic also.....

Please go through it and tell me the suggesions for suppressing the higher harnomics.................

Thanx and regards.......