Problem with comparator (ADCMP553)

[Gizmo44]

Hi all,



I am trying to recover a signal from a photodiode (few Mhz)

Because the signal is very noisy, voltage range vary and my amplifier output is differential, I decided to use ADCMP553 comparator.

My problem is that comparator outputs just follow the inputs.

I expected a logic PECL output.



Schematic and scope capture include.



Thanks for your help.

 

[barry]

That looks like you've got ground-related noise. The good news is that the noise is not causing your comparator to have false triggers. It's worth noting that your noise doesn't appear to be common-mode-(the noise is not the same on both + and - inputs). I would check your circuit grounding (as well as your scope grounding-a lot of times the ground lead on your o'scope works as a wonderful antenna.)