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The Designer's Guide Community Forum › Design › Analog Design › why DC gain of opamp with SC CMFB freq dependent?
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why DC gain of opamp with SC CMFB freq dependent? (Read 1522 times)
prcken
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why DC gain of opamp with SC CMFB freq dependent?
Sep 30th, 2012, 7:37pm  
Hi
I found that the open loop gain of the SC CMFB opamp is sampling frequency dependent, I use PSS+PAC analysis, it drops when sampling frequency increases, same opamp configuration with SC-CMFB, the gain drops to 69dB at fs=5MHz. the DC gain is 75dB when fs=1MHz , with continuous time CMFB is 77dB.
any idea?
thanks
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BackerShu
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Re: why DC gain of opamp with SC CMFB freq dependent?
Reply #1 - Nov 18th, 2012, 9:31pm  
SC circuit is equivalent to Resistor. As frequency increases, equivalent resistor reduces; thus gain reduces.
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