I have a RC low pass and ferrite bead cap filter combination on my circuit board. I am trying to use Audio Analyzer U8903 to analyze the gain response of the filter. I see quite different result in simulation and result using Audio analyzer.

In the audio analyzer if I change the generator impedance from 100 to 600 ohms or vice versa. I think the generator source impedance is impacting the results.

Has anyone used Audio Analyzer for filter analysis? Please let me know the methodology.


  • \$\begingroup\$ If you are injecting a signal in order to test a filter then the output of the signal generator is always going to cause errors when it is significant. There are no golden rules of course because some filters rely on a 50 ohm source. \$\endgroup\$ – Andy aka Feb 28 '15 at 16:20

If you have 100 or 600 ohms or whatever source resistance, you have to add that to the R in your RC. If you had a simple RC filter like 500 ohms and 100n you would get a corner frequency of 3.2 kHz. But if the source impedance of the circuit driving the filter is 600 ohms, you would get 1.4 kHz because the R in the RC is actually 600+500 or 1.1k. Big difference!


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