upper and lower switching points of this Schmitt trigger

Hi,

Can somebody tell how to modify upper and lower swtiching points of this Schmitt trigger?

Many thanks!

Re: upper and lower swtiching points of this Schmitt trigger

By adjusting input buffer and INVFB transistor sizes.

Re: upper and lower swtiching points of this Schmitt trigger

FvM said:

By adjusting input buffer and INVFB transistor sizes.

Click to expand...

I am still unable to understand how hysterisis is present.

I do not understand how the higher switching point (VIH) occurs at a high voltage value and also in the return path why does the circuit switch at a lower level voltage.

Could you please point me to a source where operation of this circuit is explained in detail?

Thanks.

Positive feedback through INVFB is creating the hysteresis. You need to refer to the characteristics of involved transistor to calculate the thresholds. The best way to visualize the circuit operation is to watch transistor currents over varying input voltage in a simulation.

I thought, the circuit operation would be quite obvious, but you should find an explantion in a digital CMOS design text book.

Schmitt trigger operation visualization

For a visualization of the Schmitt trigger operation s. this link.

Re: Schmitt trigger operation visualization

erikl said:

For a visualization of the Schmitt trigger operation s. this link.

Click to expand...

Thank you but the link does not explain the operation of the circuit I have posted.

Could somebody point me to a source where the circuit which I have posted is explained? or could somebody explain how this circuit works in more detail?

I can't explain the schematic you posted. Can't figure it out. Doesn't mean it won't work just the same.

I think understanding will be easier if you examine the op amp Schmitt trigger. Also if you build one and experiment with it.

I've used hysteresis with an op amp. I got it to work but I can't remember how the feeback loop hooked up. The hysteresis concept is sort of an oddball

I do remember it took a lot of adjusting of resistor values, before I got it to switch states at my desired volt range.

Furthermore a proper explanation really needs two schematics. One showing node volt levels when the op amp output is high, and the other when it's low.

Then you can see in each case what volt level the signal has to cross, in order to cause a change of state.

Could somebody point me to a source where the circuit which I have posted is explained? or could somebody explain how this circuit works in more detail?

Click to expand...

What's your background in designing transistor level circuits? I guess, you have a least heard a lecture in CMOS design or something equivalent. You should know some standard text books and basic descriptions of CMOS inverter behaviour, e.g. transfer characteristic, output current etc. When you apply these knowledge to a positive feedback circuit, you should be able to figure out the circuit operation by yourself. Most likely CMOS schmitt triggers are explicitely discussed in some text books. But I don't have any digital CMOS design text books and can't answer where to find a description.

I think I found a nice explanation for the Schmitt trigger function as a hysteresis controller for buck converters in : View attachment The_power_electronics_handbook_p321-323.pdf, as well as Hans Camenzind's mention of Schmitts original circuit and his transfer into a simple MOS circuit -- incl. explanation: View attachment Camenzind,Hans__Designing_Analog_Chips_p168.pdf