What does the Comparator with Hysteresis circuit do?
Latest Updated:04/01/2008
Question:
"APPLICATION CIRCUIT EXAMPLE (COMPARATOR with HYSTERESIS CIRCUIT)" is shown on the Data Sheet of the uPC393 single-power dual comparators. What operation does this circuit perform?

Answer:
A feature of this circuit is that its output is not affected even if the input signal contains a certain amount of noise (the output is influenced not only by the present input condition but also by the past input condition, that is, hysteresis).
[Operation]
Hysteresis can be given to the threshold voltage by positively feeding back part of the voltage of OUTPUT to the positive (+) input pin with R2 and R1, and the influence of a noise voltage within the hysteresis width can be eliminated.
Specifically, when the INPUT voltage rises with a sufficiently low voltage (
), OUTPUT goes high. Consequently, a positive voltage drop occurs across R1 (i.e., the potential on the pin of R1 connected the positive (+) input pin is higher than the potential on the pin connected to the VREF pin) and the potential on the positive (+) input pin goes VTH (High). This status is maintained until INPUT reaches this potential VTH (High). As soon as INPUT exceeds VTH (High) (
), OUTPUT falls low. At the same time, the voltage drop across R1 becomes negative (i.e., the potential on the pin of R1 connected to the positive (+) pin is lower than the potential on the pin connected to the VREF pin), and the potential on the pos itive (+) input pin goes VTH (low). Even if INPUT is raised after that, OUTPUT remains low (
). When INPUT is gradually lowered next, OUTPUT remains low until INPUT = VTH (low) (
). When INPUT drops below VTH (low) (
), however, OUTPUT goes high again, returning to the initial status.
[Operation]
Hysteresis can be given to the threshold voltage by positively feeding back part of the voltage of OUTPUT to the positive (+) input pin with R2 and R1, and the influence of a noise voltage within the hysteresis width can be eliminated.
Specifically, when the INPUT voltage rises with a sufficiently low voltage (






Suitable Products
Comparators |