Schmitt Trigger Calculator
Calculate threshold voltages and hysteresis for inverting and non-inverting Schmitt trigger circuits.
Component Values
Results
Transfer curve with hysteresis
How does a Schmitt Trigger work?
A Schmitt trigger is a comparator with positive feedback that creates two distinct switching thresholds. When the input rises above the upper threshold (Vth+), the output switches HIGH. It stays HIGH until the input falls below the lower threshold (Vth−). This gap between thresholds is called hysteresis.
Hysteresis is the key feature that makes Schmitt triggers so useful. On a noisy signal, a regular comparator switches back and forth many times as the signal crosses the threshold. A Schmitt trigger ignores noise smaller than the hysteresis window, producing a clean, stable output.
Non-inverting Schmitt triggers output HIGH when Vin > Vth+. Inverting configurations output LOW when Vin > Vth+. Both use positive feedback from the output to the non-inverting input to create hysteresis. The amount of hysteresis is set by the R1/R2 ratio.
Non-Inverting Vth+
Vth+ = Vcc × R2 / (R1 + R2)Key Points
- Hysteresis = Vth+ − Vth− prevents oscillation on noisy signals
- Larger R1/R2 ratio → wider hysteresis window
- Non-inverting: output follows input direction
- Inverting: output is opposite to input direction
Applications
- Touch and capacitive sensor debouncing
- Square wave oscillator with RC timing
- Level detection with noise immunity
- Digital input signal conditioning