Comparators and Schmitt Triggers Questions and Answers

Q: Schmitt Trigger is a special configuration of :

A Schmitt trigger is a positive feedback op-amp circuit.Part of the output is fed back to the non-inverting input, so once the input crosses a threshold the output is driven hard to the opposite saturation level. The feedback shifts the threshold, giving two switching levels (upper and lower trip points) and hysteresis, which makes the circuit immune to noise on slowly varying inputs.An open loop comparator switches at a single threshold and chatters with noise. Negative feedback produces linear amplifiers, not switching circuits. 'Differential input' describes every op-amp and does not distinguish the configuration.

Q: An op-amp based comparator with positive feedback is called :

A comparator with positive feedback is a Schmitt trigger.Feeding part of the output back to the non-inverting input gives the comparator two switching thresholds, an upper and a lower trip point, instead of one. The gap between them, the hysteresis, stops the output from chattering when a noisy input hovers near the threshold, and turns slowly varying inputs into clean square waves.An astable multivibrator is a Schmitt trigger with an added RC timing network that makes it oscillate on its own, so it is more than a comparator with feedback. A pulse generator is a general instrument, and an integrator uses capacitive negative feedback.

Schmitt Trigger is a special configuration of :

A.Open loop op-amp
B.Differential input op-amp
C.Positive feedback op-amp
D.Negative feedback op-amp

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: C

A Schmitt trigger is a positive feedback op-amp circuit.

Part of the output is fed back to the non-inverting input, so once the input crosses a threshold the output is driven hard to the opposite saturation level. The feedback shifts the threshold, giving two switching levels (upper and lower trip points) and hysteresis, which makes the circuit immune to noise on slowly varying inputs.

An open loop comparator switches at a single threshold and chatters with noise. Negative feedback produces linear amplifiers, not switching circuits. 'Differential input' describes every op-amp and does not distinguish the configuration.

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An op-amp based comparator with positive feedback is called :

A.Astable multivibrator
B.Schmitt trigger
C.Pulse generator
D.Integrator

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: B

A comparator with positive feedback is a Schmitt trigger.

Feeding part of the output back to the non-inverting input gives the comparator two switching thresholds, an upper and a lower trip point, instead of one. The gap between them, the hysteresis, stops the output from chattering when a noisy input hovers near the threshold, and turns slowly varying inputs into clean square waves.

An astable multivibrator is a Schmitt trigger with an added RC timing network that makes it oscillate on its own, so it is more than a comparator with feedback. A pulse generator is a general instrument, and an integrator uses capacitive negative feedback.

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