comparator shmitt trigger

[ikalogic]

Hello.

I have build and tested the circuit attached below.

It's a comparator, with a gain of 5:
Vout = (Va - Vb)*5

Its important to keep the gain low because i need high bandwidth.

The question is, how do i add some hysteresis?

For example, i need Vb (the voltage to which Va is compared) to be dynamic...

I've seen many circuits (like here: https://en.wikipedia.org/wiki/Schmitt_trigger ), but they are just comparators, and i cannot control the gain.. any clues?

Thanks!

EDIT: I am sure that the solution will be to use an inverting shmitt trigger (as decribed in wikipedia) but with some feedback on the -ve pin. Am i in the right direction?

 

[jpanhalt]

Have you seen this ap note: https://www.electro-tech-online.com/custompdfs/2012/04/AN3616.pdf

John

 

[ikalogic]

Thanks John for that app note.

However, all the circuits i found (unless i am mistaken) do not allow to control the gain... i need to limit the gain to 5 maximum.. any idea?

 

[Roff]

"Low gain Schmitt trigger": That's an oxymoron. Schmitt triggers have infinite gain at the trigger point.
I think this is one of those cases where you REALLY need to tell us what you are trying to do. Give us the big picture.

 

[crutschow]

If you want high bandwidth (fast comparator response) then use a comparator IC not an op amp. Comparators have high open loop gain and there is no gain-bandwidth limitation.

 

[ikalogic]

Thanks!

comparators will do the job perfectly

 

[audioguru]

A comparator does not have a frequency compensation capacitor (it reduces the high frequency gain of an opamp so it does not oscillate when negative feedback is applied). Then a comparator switches its output much faster than an opamp.
Because a comparator does not have a frequency compensation capacitor then it must NEVER have negative feedback like yours has.