# Non-inverting Schmitt Trigger

Discussion in 'Analog & Mixed-Signal Design' started by HappyC4mper, May 26, 2018.

1. ### HappyC4mper Thread Starter Member

Oct 13, 2017
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If you have a schmitt trigger completely designed for inverting, how would you go about inverting that signal?

I'm under the impression you can't just swap the input voltage to the V+ op amp input as that would completely mess up the calculations.

Thanks for the help.

2. ### MrChips Moderator

Oct 2, 2009
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Connect a second inverting Schmitt trigger to the output of the first.

3. ### crutschow Expert

Mar 14, 2008
20,805
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Depends upon the circuit.
Show us the circuit and we'll give a better answer.

4. ### AnalogKid AAC Fanatic!

Aug 1, 2013
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Are you talking about an opamp or analog comparator circuit? If so, your impression is correct. You must know the output impedance of the signal source, because that impedance will be part of the hysteresis calculations.

ak

May 20, 2015
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See

May 20, 2015
2,040
620
See

7. ### ian field AAC Fanatic!

Oct 27, 2012
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Pretty much - the same applies with logic device Schmidt. AFAIK: on the discrete transistor variety - you just use the other collector.

8. ### WBahn Moderator

Mar 31, 2012
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Does the second comparator need to be a Schmitt trigger?

9. ### MrChips Moderator

Oct 2, 2009
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Maybe I misunderstood the question.
I was thinking that maybe TS had a 74LS14-style hex Schmitt triggers and just needed a non-inverting output.

10. ### AnalogKid AAC Fanatic!

Aug 1, 2013
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... from the V- opamp input.

He has an opamp configured as a comparator with hysteresis. The signal of interest is connected to the inverting input, and either a reference voltage with a buildout resistor or a 2-resistor voltage divider tied to the non-inverting input. He calls this "a schmitt trigger completely designed for inverting", and wants a non-inverting equivalent; that is, one where the output goes high when the input signal is greater than the reference.

ak

Last edited: May 27, 2018
11. ### ian field AAC Fanatic!

Oct 27, 2012
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Only if the first one is really crappy.