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Design >> Analog Design >> transconductance of OTA?
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Message started by Ziad on Jan 16^th, 2012, 7:31am

Title: transconductance of OTA?
Post by Ziad on Jan 16^th, 2012, 7:31am

Hello guys
i am new member here and i am very new in OrCAD PSPICE
i have designed an OTA but i do not know how to simulate the most important character of it, gm.

i have read what you wrote about this but i did not understand :'(

could you help me fast please ::)

Title: Re: transconductance of OTA?
Post by raja.cedt on Jan 16^th, 2012, 10:38am

Connect OTA output to an voltage source whose value equal to OTA o/p common mode. And through Ac simulation find the current through voltage source. That's all.

Thanks,
Raj.

Title: Re: transconductance of OTA?
Post by Ziad on Jan 17^th, 2012, 1:14am

raja.cedt wrote on Jan 16^th, 2012, 10:38am:

Connect OTA output to an voltage source whose value equal to OTA o/p common mode. And through Ac simulation find the current through voltage source. That's all.

Thanks,
Raj.

Thank you Raj. but i told you i am very newby in modeling :-[ so could you please tell me:

what is o/p common mode? i want to simulate OTA with differential input..
should my input be DC or AC

Title: Re: transconductance of OTA?
Post by AnilReddy on Jan 19^th, 2012, 2:14am

hi,

As Raja answered, connect OTA in unity-gain mode. once you have done that you will be able to measure all the parameters that you want.

common-mode is the range of voltages that we need to have (either at input or output) such that the performance of the OTA will not deviate form the assumptions that we make during the analysis (such as "all devices are in sat." for example). common-mode will be the important specification if the circuit is driven by or driving any stage.

by the way..all the material that is needed to design an OTA or to understand how to simulate analog circuits (atleast to the basic level) is given in various text books. As it seems you are new to the design domain, my suggestion is that you first read any good book and try to get some understanding. (read the book by razavi, if you like)

Thannks
Anil

Title: Re: transconductance of OTA?
Post by Ziad on Jan 19^th, 2012, 2:37am

Well i am not that beginner :) i have designed that OTA and all MOSFETs are in saturation but i just want to know how to get Iout vs Vin curve... i mean is there a direct way or i have to do some (trick) as i read in some earlier posts? i read but i did not understand how to do it :'(
any way if you know an applicable circuit give me please

thanks a lot