13 Facts About Schmitt trigger

In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier.

Schmitt trigger devices are typically used in signal conditioning applications to remove noise from signals used in digital circuits, particularly mechanical contact bounce in switches.

Schmitt trigger was invented by American scientist Otto H Schmitt in 1934 while he was a graduate student, later described in his doctoral dissertation as a thermionic trigger.

Any active circuit can be made to behave as a Schmitt trigger by applying a positive feedback so that the loop gain is more than one.

The Schmitt trigger is toggled high when the input voltage crosses down to up the high threshold and low when the input voltage crosses up to down the low threshold.

Original Schmitt trigger is based on the dynamic threshold idea that is implemented by a voltage divider with a switchable upper leg and a steady lower leg .

The Schmitt trigger is transitioned to the high state and the output voltage is close to V+.

The classic non-inverting Schmitt trigger can be turned into an inverting trigger by taking Vout from the emitters instead of from a Q2 collector.

So, it can be converted to a Schmitt trigger by connecting an additional base resistor R to one of the inputs .

Instance, if the Schmitt trigger is currently in the high state, the output will be at the positive power supply rail .

One application of a Schmitt trigger is to increase the noise immunity in a circuit with only a single input threshold.

The net effect is that the output of the Schmitt trigger only passes from low to high after a received infrared signal excites the photodiode for longer than some known period, and once the Schmitt trigger is high, it only moves low after the infrared signal ceases to excite the photodiode for longer than a similar known period.

Schmitt trigger is a bistable multivibrator, and it can be used to implement another type of multivibrator, the relaxation oscillator.