I have designed an 2 stage opamp with all MOSFETs in subthreshold region as shown in the figure below,
I have gain of 48 dB, GBW of 60KHz, Slew rate of 0.014 V/us and Power dissipation of just 0.6 micro Watts.
Here is the Frequency response ,
I have a appreciable Phase margin of 60 degrees from the frequency response. I am a little down on noise and harmonic distortion analysis in LT spice.. But i do know that FFT of the output gives an idea of the THD.But how to calculate the percentage harmonic distortion ?
Here is a picture of FFT of the output, (Note :i am operating at 400Hz sine input)
What does this values in db mean and i do see peak at 800Hz which is an harmonic of fundamental frequency 400Hz , what should i conclude from it and how is the THD evaluated?
I would also like to know about the stability analysis of the same.