Schmitt trigger
A Schmitt trigger is an electronic device which can moderate analog signal values only to zero or one (0 / 1). It can be made of a couple transistors, or several triggers can be arranged in an integrated circuit.
- Uses
- Converting analog signals to digital
- Oscillators
Schmitt Trigger Media
Transfer function of a Schmitt trigger. The horizontal and vertical axes are input voltage and output voltage, respectively. T and −T are the switching thresholds, and M and −M are the output voltage levels.
Comparison of the action of an ordinary comparator (A) and a Schmitt trigger (B) on a noisy analog input signal (U). The green dotted lines are the circuit's switching thresholds. The Schmitt trigger tends to remove noise from the signal.
Block diagram of a Schmitt trigger circuit. It is a system with positive feedback in which the output signal fed back into the input causes the amplifier A to switch rapidly from one saturated state to the other when the input crosses a threshold.*A > 1 is the amplifier gain*B < 1 is the feedback transfer function
Schmitt trigger implemented by two emitter-coupled BJTs stages.
BJT bistable collector-base coupled circuit can be converted to a Schmitt trigger by connecting an additional base resistor to one of the bases
Schmitt trigger implemented by a non-inverting comparator
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Typical transfer function of a non-inverting Schmitt trigger like the circuit above.
A practical Schmitt trigger configuration with precise thresholds
