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Design >> Analog Design >> Output impedance of a closed loop amplifier across frequency
https://designers-guide.org/forum/YaBB.pl?num=1301934813

Message started by tron_123 on Apr 4^th, 2011, 9:33am

Title: Output impedance of a closed loop amplifier across frequency
Post by tron_123 on Apr 4^th, 2011, 9:33am

Dear Friends,

I have designed a fully differential reference buffer to be used in a SAR ADC. It is just an OTA with resistive feedback. I want to measure the output impedance of this buffer across frequency. Please guide as how to go about it or point me to the test bench which can do this measurement.

Regards
-Tron

Title: Re: Output impedance of a closed loop amplifier across frequency
Post by thechopper on Apr 4^th, 2011, 12:40pm

Hi Tron,

Since output impedance is a small signal parameter, first thing you have to do is set the operating bias point for your amplifier. After having done this next step is to apply an AC current with an ideal current source into the amplifier's output and measure the resulting voltage, swept over frequency. The ratio between the voltage and your AC current source will be your output impedance over freq.
When you are setting the bias point you can leave the AC current source in the output connected, since it will not change the amplifier's operating point

Best
Tosei

Title: Re: Output impedance of a closed loop amplifier across frequency
Post by tron_123 on Apr 5^th, 2011, 6:29am

Thanks Tosei,
I did as you said and it gave the desired results :)