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A circuit to clean up a noisy zero crossing detection output

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Etesla:
Here's the situation. I have a high speed comparator (LT1713) with the negative input tied to ground, the positive input tied to a 300 mV pk - pk sin wave at 150 khz, and the rails at +- 5V. It is for zero crossing detection on the sin wave. Ideally, this would provide me with a 50% square wave at 150 khz on the output of the comparator. Due to noise, bad grounding, and my own incompetence, however, the output of the comparator has many edges where there should only be one. I decided that to solve this problem, I would add some sort of noise immunity circuit after the comparator. The circuit I am imagining is sort of like a 'you are only allowed to change states after you have already been in one state for 'X' microseconds'. I want it to react to the 'first' rising edge it sees, as well as the 'first' falling edge. I imagine this sort of a timed hysteresis circuit should be fairly common, but my research has given me nothing so far. Anyone know what sort of circuit has this functionality?

Here's a picture in case my words didn't work:

ejeffrey:
The normal way to do this is a Schmitt trigger.  Just a resistor from the output to the positive input to add a bit of hysteresis.  It is just voltage based not time based.

Etesla:
Right, but doing that in a way that effectively cleans up my signal would also add a delay. I need the final output to switch on exactly the FIRST instance of the sin wave going above 0V, and the FIRST instance of the sin wave going below 0V...

SiliconWizard:
You could clean that up digitally by just ignoring transitions that are shorter than a given amount of time (depending on your application). Akin to debouncing.

Marco:
Use dynamic hysteresis, ie. use a capacitor instead of a resistor to feedback Q to the positive input. It will prevent the output oscillation, but it won't change the trigger point (assuming the RC time is << 1/f).

Of course the noise will still cause jitter ...

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