how to simulate fully differential opamp

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avinash

Joined: 24 Jul 2004
Posts: 170
Helped: 10

02 Apr 2005 7:01 how to simulate fully differential opamp

how the gain,ugb and phase margin can be calculated of fully differential opamp.pl help

glenjoy

Joined: 01 Jan 2004
Posts: 1028
Helped: 47
Location: Philippines

02 Apr 2005 7:26 how to simulate fully differential opamp

Gain is always computed by the external resistors, that is the property of the OP-AMP.

opamp741

Joined: 17 Jun 2004
Posts: 145
Helped: 10
Location: India

02 Apr 2005 10:40 Re: how to simulate fully differential opamp

r u talking abt hand calculation or using simulaton tools..

avinash

Joined: 24 Jul 2004
Posts: 170
Helped: 10

02 Apr 2005 12:22 Re: how to simulate fully differential opamp

dear opamp741,
i am asking to calculate gain ugb and phase margin through simulation tool.

ezt

Joined: 14 Oct 2004
Posts: 105
Helped: 21

02 Apr 2005 13:30 Re: how to simulate fully differential opamp

Hi.
I think you can simply use probes (e.g. voltage probe) to check the gain of your circuit. but before that you should set up your analysis (frequency Analysis in your case). then you will run it and you can check the results in probe window. (this is the way in almost every simulation tools, but ofcourse with some changes in names)

Regards,
EZT

v_naren
Guest

02 Apr 2005 19:52 Re: how to simulate fully differential opamp

avinash wrote:

how the gain,ugb and phase margin can be calculated of fully differential opamp.pl help

Here is the solution to your question!

http://www.designers-guide.org/Analysis/diff.pdf

and

http://www.edaboard.com/ftopic103890.html

if I have helped you could you please kindly click the "helped me" button and help me....you dont loose any points at all

Good Day!

Best of luck!

Smile

chinito

Joined: 05 Jul 2004
Posts: 133
Helped: 4

02 Apr 2005 21:12 Re: how to simulate fully differential opamp

better yet, cadence has a white paper called characterization of diff amp. It will teach you how to use spectre to find whole bunch of things.

avinash

Joined: 24 Jul 2004
Posts: 170
Helped: 10

04 Apr 2005 5:47 Re: how to simulate fully differential opamp

if i want to characterize the fully diff opamp in hspice,what should i do.

v_naren
Guest

04 Apr 2005 5:49 Re: how to simulate fully differential opamp

avinash wrote:

if i want to characterize the fully diff opamp in hspice,what should i do.

which is why I recommended

http://www.designers-guide.org/Analysis/diff.pdf

and

http://www.edaboard.com/ftopic103890.html

avinash

Joined: 24 Jul 2004
Posts: 170
Helped: 10

04 Apr 2005 6:05 Re: how to simulate fully differential opamp

dear v_naren
the pdf link given by you does not provide me the information about getting the ugb and phase margin.pl tell me some method.
moreover to calculate gain in single ended opamp,we provide ac signal to +input and connect the -ve input to output with RC .
but what should i do in case of diff o/p.

lilac

Joined: 26 Jan 2005
Posts: 18
Helped: 1

04 Apr 2005 11:59 Re: how to simulate fully differential opamp

hi avinash,
I usually provide two oppsite ac signals to input+ and input-. and of course, connect two output with load capacitors. Then do ac analysis, and check the result of AC magntude & Phase for the ugb and phase margin.

avinash

Joined: 24 Jul 2004
Posts: 170
Helped: 10

05 Apr 2005 5:07 Re: how to simulate fully differential opamp

dear lilac,
on which o/p node should i check for the gain,ugb and phase margin.moreover you havenot provided any feedback.

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naisare

Joined: 18 Oct 2004
Posts: 73
Helped: 1

05 Apr 2005 6:37 Re: how to simulate fully differential opamp

When Ac analysis is given, first it find out the dc node voltages upon which it does the frequency analysis. So, it is important that the dc voltages are established earlier. This will be a problem if u r using a switched capacitor CMFB for the diff amplifier. first u need to run the transient with the clocks of the CMFB till the opamp output reaches the stable dc voltage. U can load this node voltages as the initial node voltages and do the ac analysis on this.

lilac

Joined: 26 Jan 2005
Posts: 18
Helped: 1

05 Apr 2005 7:01 Re: how to simulate fully differential opamp

hi avinash,
yes, what I said above is the method to measure the AC open loop spec. of opamp.
Please refer to this document, I think you can get what you want to know!

avinash

Joined: 24 Jul 2004
Posts: 170
Helped: 10

07 Apr 2005 5:52 Re: how to simulate fully differential opamp

dear lilac, which document are you talking about.

lilac

Joined: 26 Jan 2005
Posts: 18
Helped: 1

08 Apr 2005 10:49 Re: how to simulate fully differential opamp

Hi vavinash,
I don't know why I cannot attach it on.
So, try one more time!
If you still cannot see it, leave your email address, maybe I can email it to you!

Sorry, but you need login in to view this attachment