About the harmonic distortion of differential amplifier

[triple_core]

Hi everyone,

I have a question about simulating the harmonic distortion of a fully differential amplifier in CLOSED LOOP.

I simulated the single output per transient analysis, transformed by FFT, then I can see large a power in the DC-part and signal frequency, small power by 2nd and 3rd harmonic distortion.

But the professor said, there should be no even-orderd harmonic distortion by fully differential design.

But in closed loop, I can only get the result.
Does anyone can answer me?

 

[watersky]

I think your waveform is asymmetry, you should check it.

 

[triple_core]

Thanks for your answer.

The waveform of single output is the same as normal opa, is symmetry.

 

[rajanarender_suram]

you will find the even harmonics because of common mode gain, but you should find 2nd harmonic lesser than 3rd. if ur CMRR is very much high than ur 2nd harmonic is very much smaller than 3rd