Created by
Created January 20, 2014
Last modified January 23, 2014
Tags hysteresis   schmitt-tirgger  


A way to set up a DC sweep to show the hysteresis loop of a schmitt trigger.

Not easy to understand but have a play to get your head round it.



A behavioural model of a Non-inverting Schmitt trigger with 0 - 5V output and parameter controlled high and low threshold levels.

Input provided by behavioural 5V source with an parameter controlled sweep to show the classic hystersis loop of a schmitt trigger.

The simulation set up and V(out) plot expression looks complicated but is a way of plotting V(out) so that it looks correct when V(in) is swept from 0 to 5V in the "up" direction (up = 1) and still looks right in when V(in) is swept from 5V to 0 in the "down" direction (up = 0).

A behavioural current source with a 1R load and a 1pF parallel capacitance is used in preference to a voltage source (with or without a series resistance/parallel capacitance to ground) because Norton equivalent circuits generally calculate faster and converge better than Thevenin equivalent sources. Band limiting behavioural sources also helps convergence.

Simulate > DC Sweep > Run DC Sweep


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