I designed an active low-pass filter by using AD797 and analog filter wizard as http://www.analog.com/designtools/en/filterwizard/Share?id=1865 . I expected that this filter will suppress the harmonic signal from a function generator. Normally, a function generator has the harmonic over then -70dB. The datasheet of AD797 has 100 or 120dB THD. So, I use it for my active low-pass filter.
My function generator has -75dB second harmonic and -85dB third harmonic. After I assembled the evaluation board as EVAL-FW-MOTHER and EVAL-FW-LPSK1. I checked the filter did not suppress the harmonic signals and increased about 2dB. I wondering this is normal or abnormal working of AD797?
And I need one single tone signal which has harmonic under -100dB. Would I get the recommendation or direction to get it?