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Interesting PSRR calc of Op amp

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jonnybgood

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Below is link of a simple method used to measure the PSRR of an op amp. He uses an integrator, switches different supply voltages and note the difference in output voltages.

Can anyone explain what is going on exactly?

HTML: 
http://www.analog.com/static/imported-files/tutorials/MT-043.pdf
 

You really don't need A1 if you are only interested in measuring the PSSR - just use the DUT (of course closing the feedback on the inverting input).
The only reason for that circuit is that you can use the same jig for the CMMR too.
 
In order to eliminate the effect of the output impedance of the DUT on the result, a buffer (A1) has been used. If you eliminate it, you loose accurancy in the measurement, especially for high PSRR.
 
albbg said:
In order to eliminate the effect of the output impedance of the DUT on the result, a buffer (A1) has been used. If you eliminate it, you loose accurancy in the measurement, especially for high PSRR.
Click to expand...

what do you think would be a suitable value for the capacitor in the buffer A1?
 

albbg said:
In order to eliminate the effect of the output impedance of the DUT on the result, a buffer (A1) has been used. If you eliminate it, you loose accurancy in the measurement, especially for high PSRR.
Click to expand...
I doubt that a 10K load may have a big effect on PSRR, if at all. By the way: 10K is the DUT load used by Analog in their setup.
 

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