why THD is degrading at HIGH gain settings in PGA..

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balabrahmachari

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Hi,
i am simulating a low noise PGA in which i have observed the THD degradation at higher gain settings. Why?

normally we see the THD degradation for lower feedback resistance values(where gain is comparatively less) due to loading effects.

but got puzzled why at high gain settings?

Can anyone help me please?

thanks,

regards
Bala
 

Can you give the circuit diagram ....
I think with higher gain the swing of the output signal is increasing. Can your output stage tolerate that swing. If no then the peaks of the signal might get saturated (chopped off). Increasing distortion and introducing higher harmonics.
 

I do not know what you are using for your PGA.
If it is an opamp then it has negative feedback. The negative feedback reduces its output distortion and makes its voltage gain less.
When its voltage gain is higher then its distortion is also higher.
 

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