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Design >> Analog Design >> measuring op amp specs
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Message started by mixed_signal on Oct 30^th, 2011, 12:53pm

Title: measuring op amp specs
Post by mixed_signal on Oct 30^th, 2011, 12:53pm

Hi,
I have designed a single input single output amplifier for low power applications. It has dynamic biasing and has two phases: biasing phase and amplifying phase and has clocks. I want to measure the slew rate, settling time, input reffered noise, input comon mode range, output common range, offset. How can i measure them systematically.

For slew rate measurement, i know that opamp is configured as voltage follower and then step input is given. What should i do in case single input single output case?

Should i use any feedback?

Title: Re: measuring op amp specs
Post by raja.cedt on Oct 31^st, 2011, 1:26pm

What do you mean by dynamic biasing, is bias current chages over the operation? Any how to for all measurements use feedback at least dc -ve fb and may be for ac openloop is ifne.

Thanks,
raj.

Title: Re: measuring op amp specs
Post by mixed_signal on Nov 1^st, 2011, 7:06pm

Yes the bias current changes and more important is that the amplifier has a biasing phase where it is switched to biasing circuitry and gets biased. During amplifying phase input is applied and biasing circuit is cut off. There are capacitors to keep it biased.

Title: Re: measuring op amp specs
Post by weber8722 on Nov 17^th, 2011, 8:03am

BTW, measuring SR as follower is not always sooo good. Image your output is rail-to-rail, but input not. So you will overdrive the input, if this is not the case in your real application you may get inconsistant results.
Better always do both standard tests and test very close to the actual application (maybe a 100X-amp, not a unity-gain-buffer).