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tranconductance amplifier

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nisha gupta

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hi
i have design a transconductor amplifier with CMFB. i have used 250K resistance for resistive divider from analog lib. now i want to replace it with UMC component. maximum resistance in UMC65nmlib is 124K so connected two resistance in series. but TCA performance degraded alot. m i doing something wrong.
 

Any IC resistor has distributed capacitance to substrate. Large resistor typically has large area which results with high capacitance (~1fF/µm²).
Replace UMC resistors with those from analogLib and add estimated capacitances and check if the behaviour is similar.
 

nisha gupta said:
i have design a transconductor amplifier with CMFB. i have used 250K resistance for resistive divider ...
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It is also possible that a resistive load of 250kΩ is too much for your amp. Try with higher resistance values or stronger amp output.
 

It might not be the resistor divider that is affecting you but the parasitic capacitances associated with the large resistors that might be affecting it.

Maybe you could run some simple frequency analysis on the UMC resistor vs the Ideal resister to know how different they are.

I am guessing that the circuit worked fine with the 250K resistor from analoglib. so you can try what Dominik suggested.
 

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