Hi Hal,
On 02/25/2015 10:44 AM, Hal Murray wrote:
[email protected] said:
Yes. You should not use a logic gates with analog input signals. Using a
74LVC14 helps due to its Schmitt-Trigger input. I think the proper solution
here would be to use a high speed comparator instead (with hysteresis).
The Schmitt trigger mostly avoids glitches on the output. Does it do
anything to reduce timing noise if the input signal is clean enough that it
doesn't make any glitches?
No, it just avoids flipping state at the transition point(s).
The trigger jitter problem remains the same, regardless if it is at one
voltage (comparator with no hysteresis) or two voltages (comparator with
hysteresis aka Schmitt trigger), the slew-rate at the comparator voltage
and the noise will interact to create trigger jitter. If you want to
improve on that the main solution is to improve slew rate, but naturally
careful filtering can help.
It is all to often that I have encountered people to confuse the
Schmitt-trigger for improving the timing jitter. It's movement in two
different domains, voltage (schmitt trigger) and time (trigger jitter).
Cheers,
Magnus
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