Compensating external amplifier frequency response

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madu

7th August
Posts: 1

I'm using a CS328A with CS700A function generator.

Is it possible to compensate the frequency response introduced by an external amplifier?

My measurement setup contains and external amplifier driving a DUT.
What I have in mind is to record the the frequency response of the amplifier and compensate for it, when I'm measuring my DUT.
Other devices allow to create a equalization file.





bartschroder

8th August
Posts: 427

Hmm - because the Gain/Phase measures both the Stimulus (Chan A - the output of your amplifier) and the Response (Chan B - the output of the DUT), you do not really need to worry about what the amplifier does.

However, if you really want to normalize Gain/Phase for the amplifier you can use the FRA Control Panel/Analysis Type/Calibrate Probes to do this. This will normalize Gain = 0dB and Phase = 0 degrees. The net result will be much the same - except at high frequencies where the cable and probe errors become significant. It is more the cable and probes that you are compensating for.

So the steps are:
1. attach both the A and B channels to the output of your external amplifier.
2. Set up the FRA frequency sweep range and amplitude. (Maybe do Auto to check the Scope Graph is capturing the amplitude range correctly).
3. Choose Analysis Type/Calibrate Probes and Start Sweep.
4. Now do Gain/Phase, with the connection as you have it, and the Probe Corr led on. You should find that the Gain/Phase are now flat at 0dB and 0 degrees.
5. Do a File/Save As to save the current setup, which includes the correction table. By doing a File/Open, you can reload the correction set.
6. Now include the DUT in the loop, and the Gain/Phase should represent the DUT. Chan A is the stimulus, and Chan B is the response.

Notes:
1. if you change the frequency range or steps per decade, you should redo the probe correction.
2. For best accuracy have both channels use the same amplitude range.
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