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ADRF6518 filter shape

Question asked by iw0cnb on Feb 14, 2016
Latest reply on Feb 15, 2016 by jdobler


I have noticed that the frequency response of the ADRF6518 is sensitive to load impedance.

I need to DC couple the ADRF6518 output to an ADC which is supplying the common mode DC offset voltage.

Which is the correct impedance to terminate the differential outputs of the ADRF6518 to have a filter response matching the datasheet figure 17? (peaking around 0.5 dB)

I initially tested the evaluation board in single ended mode, and obtained results consistent with fig.17. Then I modified the evaluation board isolating the transformer, output in AC-coupled differential mode with 400 ohm load but obtained much higher peaking and ripple in frequency response (measured with a high impedance probe to spec. analyzer).

Any help and suggestion is greatly appreciated


Massimo Marini