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Differential amplifier and source degeneration between sources of differential pairs

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ICdesignerbeginner

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I want to work on op-amps but linearity of the op-amps differential pair is very low. So to increase linearity I have read that there is a techinque to linearize the differential pair. whats the difference between using a passive resistor for source degeneration and MOS device in triode region to improve linearity.

If I use triode MOS for source degeneration then what gate voltage should I apply. What biasing circuit for gate voltage of triode MOS?
 

Op-amps are usually operated in feedback circuits that don't need linear input stages because the input voltage is zeroed. It's different e.g. for OTA. What do you want to achieve?
 

Yes, I am talking about OTA. I want to linearize the input differential pair of OTA.
 

What do you mean by 'the input voltage is zeroed'. For the differential pairs of OP-AMP we also apply differential volatges then how input voltage is zeroed.

I am a grade1 student. I cant understand this point of yours.
 

I was mentioning the simple fact, that op-amps are used in feedback circuits and don't take advantage of source degeneration.
I cant understand this point of yours.
No problem, don't tackle all problems at once, go for the OTA linearizing problem first.

Did you notice this recent thread about source degeneration with MOSFET?
https://www.edaboard.com/showthread.php?t=372939
 

Thank you for sharing this thread. Its really helpful.

Are OTAs used in Open loop without a feedback?
 

I want to work on op-amps but linearity of the op-amps differential pair is very low. So to increase linearity I have read that there is a techinque to linearize the differential pair. whats the difference between using a passive resistor for source degeneration and MOS device in triode region to improve linearity.

If I use triode MOS for source degeneration then what gate voltage should I apply. What biasing circuit for gate voltage of triode MOS?
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whats the difference between using a passive resistor for source degeneration and MOS device in triode region


When you put resistor you cannot change it in real life. But when you use transistor you can switch it on or off and also change the linear resistance (rds) by changing the gate voltage so in second case you have made a variable gain amplifier.

Check Current stealing method also for linearizing your OTA or Opamp.

There are 2 methods which are popular:

1) Source Degeneration OTA
2) Current Stealing OTA

and also search for Source degenerated MOS transconductor using MOS transistors.
 

Thankyou for replying. Is current stealing method also called bump linearization? Can you suggest some paper on this. I cant find any good paper.
 

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