BeginnerTopic 22 of 104Electronics & Embedded
Comparators and Schmitt triggers
Decide if an input is above a threshold; hysteresis rejects noise.
In depth
A comparator outputs high or low depending on which input is larger. Noise near threshold causes chatter; a Schmitt trigger adds positive feedback hysteresis, with thresholds V_T±. Used for level detection, squaring signals and relaxation oscillators.
Key points
- Open-loop op-amp as comparator
- Dedicated comparators are faster
- Hysteresis voltage set by divider
ExampleA thermostat uses hysteresis to prevent rapid switching.
What is Comparators and Schmitt triggers?
Decide if an input is above a threshold; hysteresis rejects noise.
Why is it important to understand comparators and Schmitt triggers?
Comparators turn analogue signals into digital decisions, and Schmitt triggers add hysteresis to reject noise near the threshold.
What is hysteresis?
The difference between the upper and lower switching thresholds, which prevents chattering when the input is noisy near the threshold.
Why does a comparator need hysteresis?
Without it, noise near the threshold causes rapid switching and false triggering, so a Schmitt trigger stops the output chattering.
How is Comparators and Schmitt triggers used in practice?
Typical applications include detecting when a battery voltage falls below a safe level, cleaning a noisy switch signal before it reaches a microcontroller and triggering an alarm when a temperature crosses a limit.
What should I learn before Comparators and Schmitt triggers?
Study "Integrator and differentiator" first (topic 21 of 104 in Electronics & Embedded). It covers the groundwork this topic builds on.
What are the key points of Comparators and Schmitt triggers?
Open-loop op-amp as comparator. Dedicated comparators are faster. Hysteresis voltage set by divider.
Can you give an example of Comparators and Schmitt triggers?
A thermostat uses hysteresis to prevent rapid switching.
What comes after Comparators and Schmitt triggers?
The next topic is "Active filters", which builds directly on this one.
How difficult is Comparators and Schmitt triggers?
It is classed as Beginner in Electronics & Embedded (topic 22 of 104). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.