Describe Schmitt trigger.

Schmitt Trigger

A Schmitt trigger is a comparator circuit with positive feedback that exhibits hysteresis, meaning its output depends not only on its current input but also on its previous input. This hysteresis, or switching threshold difference, causes the circuit to have two distinct switching points, one for rising input signals and one for falling input signals. As a result, the Schmitt trigger can be used to clean up noisy signals, generate square waves, and perform other digital logic functions.

Basic Operation

The basic Schmitt trigger circuit consists of two resistors, two diodes, and an operational amplifier (op-amp). The op-amp is configured as a comparator, with its non-inverting input connected to a voltage reference and its inverting input connected to the input signal. The positive feedback loop is created by connecting the output of the op-amp back to the inverting input.

When the input signal is below the reference voltage, the op-amp's output is low. This causes the positive feedback loop to drive the op-amp's output even lower, until it reaches the negative saturation voltage. When the input signal rises above the reference voltage, the op-amp's output goes high. This causes the positive feedback loop to drive the op-amp's output even higher, until it reaches the positive saturation voltage.

The switching thresholds of the Schmitt trigger are determined by the values of the resistors and diodes. By carefully selecting these values, the Schmitt trigger can be designed to have the desired switching points.

Applications

Schmitt triggers have a wide variety of applications, including:

• Noise reduction: Schmitt triggers can be used to clean up noisy signals by removing unwanted fluctuations.
• Square wave generation: Schmitt triggers can be used to generate square waves from a sine wave or other non-square waveform.
• Digital logic: Schmitt triggers can be used to perform various digital logic functions, such as AND, OR, and NOT.
• Level detection: Schmitt triggers can be used to detect when a signal reaches a certain level.
• Oscillators: Schmitt triggers can be used to build oscillators, which are circuits that generate periodic waveforms.

Advantages and Disadvantages

Advantages:

• High noise immunity
• Well-defined switching thresholds
• Fast response time
• Low power consumption

Disadvantages:

• Limited input voltage range
• Output is not rail-to-rail
• Hysteresis can cause problems in some applications

Conclusion

The Schmitt trigger is a versatile circuit that has a wide variety of applications. Its hysteresis makes it particularly useful for cleaning up noisy signals and generating square waves.