using pmos based OTA-C (Gm-C) filter as an averager

I'm designing a pmos based OTA-C filter to be used to average out input values. The issue is: i'm getting correct average value for certain inputs but not for all.

I believe it is due to non constant gm offered by the OTA. Which part of the OTA i should correct.

Its a classic two stage pmos based input differential topology (balanced).

Thanks

Re: using pmos based OTA-C (Gm-C) filter as averager

analogturbo said:

I'm designing a pmos based OTA-C filter to be used to average out input values. The issue is: i'm getting correct average value for certain inputs but not for all.

I believe it is due to non constant gm offered by the OTA. Which part of the OTA i should correct.

Its a classic two stage pmos based input differential topology (balanced).

Thanks

Click to expand...

* What means"certain inputs but not for all" ? This sentence has no information at all
* What is the source of your believe? Why is the gm not fixed in your design?

Re: using pmos based OTA-C (Gm-C) filter as averager

Thank LvW for your reply.

Inputs are waveform recovered from a source. So when i say certain inputs it means that i applied a waveform V1 i get V1avg_out which is the average value of V1. But when i apply an input V2 or V3 etc... i get Vavg_out which is expected value +/- an offset value of few tens of mV.

As far as gm is concerned i got it wrong previously, i ignored the fact that as the input changes, the gain has to change accordingly.

Re: using pmos based OTA-C (Gm-C) filter as averager

analogturbo said:

As far as gm is concerned i got it wrong previously, i ignored the fact that as the input changes, the gain has to change accordingly.

Click to expand...

What does this mean? Do you want or require such a change?