Hi~~~
My sigma delta modulator has second harmonic distortion like attached file
But i see papers there has no second harmonic just has third harmonic.
Is anybody know what cause second harmonic distortion.
My sigma delta is switch-capacitor with fully differential OPA.
Hi~~~
My sigma delta modulator has second harmonic distortion like attached file
But i see papers there has no second harmonic just has third harmonic.
Is anybody know what cause second harmonic distortion.
My sigma delta is switch-capacitor with fully differential OPA.
we happened to have similar problem with our silicon.
we have 2nd, 4th,... at ~-40dBc.
only that the main tone is not at 0dBV,
at -40dBv instead.
we are still looking for the cause...
Hi, sixth
by
Check carefully if the output swing of the opamp within the linear range.
sixth:
thanks for you reply
I will check it carefully.
jcpu:
I early designed SDM not had 2nd distortion .
My spec is third order and the two and third OTA of SDM has ideal current in there,
Then i use current mirror to replace the ideal current,the 2nd appear.
The OTA's common mode output has some change , about 15mV below CMFB.
I think that is another possibility of 2nd distortion.
If you solve this problem please tell me the reson.
thanks a lot~~!!
Basically, the even order haomonics come from the mismatch on fully-differential circuits. This happens in real circuits. But in simulation the mismatch is not seen at all. I suggest you check your CMFB and the output impdeance of the tail current-source in the differential pair.