[SOLVED] Front end PCB setup for Sigma Delta Converter measurements

[jgk2004]

Hello all,

I am trying to measure my new sigma delta ADC and I am having problems with harmonic distortion coming from my generator which is then limiting my SNDR of my ADC. I do have a filter removing 40dB of my harmonics coming from my SMA 100A generator but what I am seeing on the PCB is that after my balun my harmonics are increasing by 14dB... Does this make any sense? Do I have some kind of reflections creating harmonics... I wouldnt think this is possible.... does anyone have a recommend Frontend setup for measuring high performance ADCs Right now my balun is a TC1-1-13MA+. Then I feed in my CM by two 50ohm resistors on each output of the balun. then this feeds right into my ADC

Any help would be greatly appreciated.

Jgk

 

[skal81]

You can try to add a bandpass filter between your SG and the ADC input. It helps removing the distortion components from the SG.
You can also try using a differential buffer amplifier instead of a balun. Depending on the ADC input type it can helps improve distortion.

 

[jgk2004]

Thanks for the input,

I was already bandpass filtering my input. I found out that my balun was just on the boarder of the datasheet specifications of my input signal and injecting second order harmonics destroying my input signal. Problem solved!

Thanks
Jgk