6. Biestable Amp Op

Schmitt trigger is essentially a multivibrator having two stable states. The output remains in one of the stable states indefinitely. The transition from one stable state to the other takes place when the input signal changes appropriately (triggers appropriately). Bistable operation needs an amplifier with a regenerative (positive) feedback with loop gain greater than unity. The circuit is often used to convert square waves with slowly varying edges to sharp edges required in digital circuits. It is also used for debouncing the switches. Schmitt trigger is otherwise called regenerative comparator. In this comparator circuit a positive feedback is added. The input voltage Vi triggers the output Vo very time it exceeds certain voltage levels. These voltages are known as upper threshold voltage (VUT) and lower threshold voltage VLT . The difference between the two threshold voltages (VUT –VLT) gives the hysteresis width.