joel
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I wonder if you smart people could answer a how-to question for me. I'd like to evaluate the small-signal noise of a differential opamp. The spice manual explains that the .noise statement takes two arguments. The first is the output variable defining the output voltage from which the noise is evaluated. The second is the indepenant source to be used as the noise input reference. So if I want to evaluate the noise at the differential outputs of an opamp with single-ended input, I'd type
.noise v(outp,outn) Vinp
Where outp, outn are the output nodes of the circuit, and Vinp is the independent voltage source defining the voltage of the input node of the circuit, e.g. Vinp inp VCM 0 AC 1 .
This seems to work. But if I want to evaluate the noise of the circuit with a differential input configuration, do you know the syntax? I'd be defining the input like this:
Vinp inp VCM 0 AC 0.5 $inp positive polarity input node Vinm inm VCM 0 AC 0.5 180 $inm negative polarity input node
My confusion is that I'm now driving the circuit with two independent sources. Maybe it doesn't matter, or I need just do a 6dB adjustment?
I hope my question make sense. Thanks for any knowledge you can offer me!
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