OTA-C Filter design and its tuning

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Hi

I want help in OTA-C filter design. OTA can be tuned its electronically tunable device. If OTA is a linear OTA using source degeneration MOS then do I have to vary the resistance of the source degenerated MOS or do I have to vary the biasing current to tune the OTA to vary its gm?

Secondly, If I have dsigned a GM-C filter then do I have to tune all OTAs resistance incase of source degenerated MOS used in OTA or tune all transistors biasing currents or just can I vary the current or resistance of one OTA only?

Thanks & regards
 

Source degenerated OTA gm can be no longer controlled by a current source. Need to tune the degeneration resistor. Unfortunately variable resistor linearity isn't necessarily better than of a non-degenerated OTA.
do I have to tune all OTAs resistance incase of source degenerated MOS used in OTA or tune all transistors biasing currents or just can I vary the current or resistance of one OTA only?
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Depends on the filter structure. Usually you have to tune multiple OTA stages, e.g. all integrators - two OTAs per bi-quad. Otherwise filter parameters like Q or gain vary unintentionally.
 

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