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Fully differential (differential in - differential out) OpAmp offset simulatoin (Read 346 times)
7IC7
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Fully differential (differential in - differential out) OpAmp offset simulatoin
Apr 02nd, 2019, 12:05pm
 
Hello everyone,

I have a question about the offset simulation of the fully differential amplifiers (differential in - differential out). I am not able to find a good resource that provides an understandable test bench (for offset simulations).

The only link that I found is this one which is not complete:

https://designers-guide.org/forum/Attachments/offsetFullyDiffopampV1.pdf

Have you done this type of simulation before? If yes, please help.

Regards,
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Ken Kundert
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Re: Fully differential (differential in - differential out) OpAmp offset simulatoin
Reply #1 - Apr 2nd, 2019, 5:36pm
 
Generally you just provide some feedback and then measure the difference in voltage between the two inputs.

Placing the amplifier in a unity gain configuration works well.

You might want to take a look at https://designers-guide.org/analysis/diff.pdf for general information on how to test differential circuits.

-Ken
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Salim2019
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Re: Fully differential (differential in - differential out) OpAmp offset simulatoin
Reply #2 - Apr 7th, 2019, 2:14pm
 
Hi,

Connect your amplifier as a unity gain buffer, sweep differentially your inputs and record the output.
I will assume you are working with single supply operation let say 3.3 V. So use two DC sources with 1.65 at each input with a variable callled X, now sweep X from -1.65 to 1.65,

Now you have two output signals, ideally they must intersect at the point of X=0. any shift from this point is your offset voltage. Note I am talking about the x-axsis.

Hope I could answered your question
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kabir_fakir
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Re: Fully differential (differential in - differential out) OpAmp offset simulatoin
Reply #3 - May 3rd, 2019, 2:09pm
 
Salim2019 wrote on Apr 7th, 2019, 2:14pm:
Hi,

Connect your amplifier as a unity gain buffer, sweep differentially your inputs and record the output.
I will assume you are working with single supply operation let say 3.3 V. So use two DC sources with 1.65 at each input with a variable callled X, now sweep X from -1.65 to 1.65,

Now you have two output signals, ideally they must intersect at the point of X=0. any shift from this point is your offset voltage. Note I am talking about the x-axsis.

Hope I could answered your question


Yes SALIM is right. I have done same procedure with fully differential OTA.

By the way, I have followed the doc cited by Ken Kudert.

Good luck!
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Always a learner and will be .
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