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Output of OTA with capacitor or without capacitor

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ICdesignerbeginner

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Hi

Can someone tell me if I am simulating OTA circuit do I hav eto placea capacitor or resistor at the output or not?What would be the difference if I do not place any capacitor resistor at the output?

I tried I observed the change in the phase margin only if I place a capacitor? is there any other parameter difference

Thanks
 

Hi

Can someone tell me if I am simulating OTA circuit do I hav eto placea capacitor or resistor at the output or not?What would be the difference if I do not place any capacitor resistor at the output?

I tried I observed the change in the phase margin only if I place a capacitor? is there any other parameter difference

Thanks

If you place a resistor, then make sure the resistor is much larger than your output impedance else your gain will drop. To drive resistors, you need to follow your OTA stage with a source follower.
Placing a capacitor will change the location of your pole and it is quiet expected you will see a phase margin variation.
 

A good practice of designing OTA ( I assume here OTA, high output Z) is to keep the load as a non-dominant pole far from the dominant one which sets the gain and the BW. Following this, you will obviously ensure proper PM for your circuit. Hence, it would be applicable for different capacitive load in 'tolerable' range and you should not see any major impact of this capacitive loads on your OTA. In the case you will be driving some other resistive load, make sure that the OTA has the driving capability for a certain resistive sizing, will demand high current and anyway the non-dominant pole will be far away from the gain or dominant pole.

Hope this helps.
 

Can someone tell me if I am simulating OTA circuit do I hav eto placea capacitor or resistor at the output or not?

f you place a resistor, then make sure the resistor is much larger than your output impedance else your gain will drop. To drive resistors, you need to follow your OTA stage with a source follower.
Placing a capacitor will change the location of your pole and it is quiet expected you will see a phase margin variation.

Hello,
Isn't simulating without capacitors and resistors is testing the the OTA in no load conditions? I think this is done as a laboratory experiment to see the behavior of an OTA. Moreover, correct me if I'm wrong, an output capacitance is specified (the OTA is designed to drive a certain max capacitance load e.g. the Cgs of the transistor being driven or the input of the next stage). So the OTA should be designed with the specified output load in mind.
 

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