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fully-differential opamp: how to simulate its FFT spectrum to check the SNDR (Read 435 times)
A.D.J
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fully-differential opamp: how to simulate its FFT spectrum to check the SNDR
Jun 08th, 2017, 9:14am
 
Hi, everyone.
The fully differential opamp is used in MDAC of a pipelined ADC.
I want to plot the FFT spectrum to check its SNDR.

For single-ended output, connect the output to negative input to build up the unity gain buffer. And then provide the sinewave to the positive input. Then we can plot the FFT of the output.

But for the differential output, how to plot FFT?

Thank you.
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davidshw
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Re: fully-differential opamp: how to simulate its FFT spectrum to check the SNDR
Reply #1 - Jun 8th, 2017, 5:39pm
 
maybe you can try this configuration:

Vin=VICM+Asin(wt)
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A.D.J
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Re: fully-differential opamp: how to simulate its FFT spectrum to check the SNDR
Reply #2 - Jun 9th, 2017, 11:38am
 
Thank you so much.
Leaving the negative node of the output floating, it doesn't influence the circuit?
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davidshw
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Re: fully-differential opamp: how to simulate its FFT spectrum to check the SNDR
Reply #3 - Jun 11th, 2017, 7:09pm
 
I think the CMFB will cause the Von to be 2*VOCM-Vop. Maybe the output loading should be added both at Vop and Von.
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