Hysteresis without Feedback

Only sequential logic. A Schmitt is purely combinatorial. It's outputs are a function of its input(s) - only. Need feedback to make it work.

Okay, so what's the state of a Schmitt trigger when its input lies between the rising and falling thresholds.

Which a Schmitt trigger has.

Tim

Outputs are NOT a function of inputs alone when the input is in the hysteresis region.

There's stored charge, in the base of the turned-on transistor, that holds the state. That feedback loop is unstable without the stored charge limiting the slew rate. If you model the base Rbb and capacitance, you can initialize it so Spice always starts it up in your preferred state when the input is in the hysteresis region.

In LTspice: .IC V(Q1B) = XX volts

Wherever do you get that from?

I thought you were asking about a transformer core. Your question was excessively vague.

What is your point?

NT

Do pay attention.

Then it's not a Schmitt, it's a latch.

Don't be absurd.

I thought you were following the thread. I guess that's too much to expect.

Ach so!

I wanted something I could poke into white proto breadboard :)

piglet

Precisely!

piglet

OK, thanks. So it does come out of a diff pair like piglet said.

George h.

I am. But I don't read minds. Your question was so vague it was hopeless.

NT

Where did bird-brain krw get that idea? The 'subject at hand' is hysteresis. And he can't even spell 'Schmitt' ;-)

Yup. ...Jim Thompson

A latch (Eccles-Jordan bistable circuit) is a two-transistor circuit with positive feedback (collector-to-base coupling). A Schmitt is a two-transistor circuit with positive feedback (emitter coupling).

Both are bistable, both have hysteresis. The bistable nature implies an INTERNAL state, which is why hysteresis in a latch implements memory, as does hysteresis in a magnetic core or a Schmitt trigger.

The similarities are profound, the differences are... minor details.