Help me plot the gm of OTA versus the differential input using Spectre

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safwatonline

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hello,
i want to plot the gm of OTA ,versus the diffrential input , i am using spectre , can any one help me?
i attached a picture of what i want to draw taken from a papper.
thnx
 

Re: gm

I guess your question is: Plot GM with ID or something like that....

If so, then check for a Calculator tool within Cadence. Google it, you should find some kind of tutorials..

I think there has been many discussions about Calculator in this webforum. Search it.

Srivatsan
 

Re: gm


well ,,can you upload some of these tutorials??
 

Re: gm

make dc analysis with the differential input as a variable. then after running the analysis, u can draw the gm of the input pair from the result browser window
 
Re: gm

Check these attachments.. The credit for the tutorial goes to the concerned author.

I hope they are useful.

Srivats
 

Attachments

  • cadence_manual_1857.pdf
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    safwatonline

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Re: gm

Provides a good overview of Cadenec suite of tools;what does it mean to this question?
 

gm

hello,
thnx for the replies,
i need to make this plot at a certain i/p freuqncy ,(i.e. not DC analysis).
any suggestions.
 

Re: gm

Very simple. Do AC sweep at certain frequency.
But there is some trick. Apply AC/DC source with to inputs of OTA though voltage controlled voltage sources (vcvs) with gain +0.5 and -0.5. DC voltage of this source is differential voltage between inputs (VDM). So u can do AC sweep on VDM variable at certain frequency and plot Gm = Iout_ac/Vin_ac vs. VDM.
I attach testbench picture for opamp. I use verilog-a negative feedback to eliminate offset voltage of opamp. For OTA i think u should to short output of OTA on certain potential, and eleminate offset of OTA under zero output current condition. I hope u can do it by yourself.
Look reference link for good tutorial:
 

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