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safwatonline
Joined: 19 Nov 2005
Posts: 1352
Helped: 164
Location: EGYPT
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 22 Apr 2006 16:37 gm |
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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
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srivatsan
Joined: 04 Aug 2004
Posts: 183
Helped: 4
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| 24 Apr 2006 3:50 Re: gm |
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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
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husseinadel
Joined: 25 Jan 2006
Posts: 184
Helped: 12
Location: EGYPT,CAIRO
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| 24 Apr 2006 8:53 Re: gm |
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| srivatsan wrote: |
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 |
well ,,can you upload some of these tutorials??
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eng_Semi
Joined: 03 May 2005
Posts: 339
Helped: 30
Location: Egypt
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| 26 Apr 2006 10:46 Re: gm |
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| 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
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srivatsan
Joined: 04 Aug 2004
Posts: 183
Helped: 4
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| 01 May 2006 3:49 Re: gm |
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Check these attachments.. The credit for the tutorial goes to the concerned author.
I hope they are useful.
Srivats
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samuel
Joined: 15 Nov 2004
Posts: 272
Helped: 1
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| 02 May 2006 15:19 Re: gm |
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| Provides a good overview of Cadenec suite of tools;what does it mean to this question?
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safwatonline
Joined: 19 Nov 2005
Posts: 1352
Helped: 164
Location: EGYPT
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| 02 May 2006 22:27 gm |
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hello,
thnx for the replies,
i need to make this plot at a certain i/p freuqncy ,(i.e. not DC analysis).
any suggestions.
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DenisMark
Joined: 16 Sep 2005
Posts: 314
Helped: 64
Location: Russia
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| 21 Jun 2007 8:19 Re: gm |
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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:
http://www.edaboard.com/viewtopic.php?p=718044#718044
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