Dear experts,
I am using AD9697 ADCs on a data acquisition board to digitize quite narrow pulses (FWHM ~ 30 ns) coming from a laser through a fast PIN diode.
So this pulse is unipolar and to get the maximum dynamic range, I put the baseline near the lower rail of the ADC.
The main input circuit is done with a ADA4927 to make single-to-differential conversion and baseline setting.
The baseline is generated by AD5691. The schematics of the input stage is put below
For the moment I simulate the laser pulse with an AWG which generates a positive pulse and I can perform the acquisition on my board. Here is a typical pulse I get
The point is if I zoom around the baseline, I do see an undershoot I don't have on the input signal:
Furthermore, this undershoot is changing with the level of the baseline. For instance, if I put the baseline not far from the midscale, I see almost no undershoot:
I have checked with a DSO that at the input of the ADC, the pulse is clean without any undershoot.
Is this behavior something expected with this ADC or did I miss something in the settings to avoid it ?
Thank you very much for your advice.
Best regards
Marc
