Need an op-amp expert !

All,

I think I've messed up an op-amp (actually a comparator) design at
work.

I'm using an LMV321 (dual low voltage op-amp) operating at 4V.

Using one half as an amp, it seems to amplify a 50KHz square wave to
about 1V peak to peak quite happily.

Then comes the trouble !

The 1V square wave is connected to a clamp (DC restorer) with the
output square wave bottom side approx 1.6VDC (so top side should be
2.6V). That connects directly to the - input of the other half of the
LMV321 used as a comparator.

The reference voltage (2.1V) connects to the + input of the comparator
via 22K. There is a 330K feedback resistor from output to + input for
Schmitt trigger action.

The output of the comparator seems to change the mark/space duty cycle
(weird). The problem gets much worse at cold. Adjusting the voltages
slightly on the comparator inputs seems to vary the output duty cycle
(weird).

My best theory is that an LMV321 is not fast enough as a comparator
(even though it amplifies the 50KHz to 1V peak to peak quite happily).

I have cunning plan. An LMH6658 is an RF op-amp that is pin compatible
and shouuld drop in for the LMV321.

Has anybody any experience with using the LMH6658 as a comparator ?
Will it make an OK fast(ish) comparator ? Are there any circuit tweaks
to speed up the LMV321 ? Do op-amps get slower at cold (-30C) ?

Please help !

Thanks,

Jim


.

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