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longstar, i guess that's what elec_boy means.
elec_boy, just look to any datasheet of comarator,
for example **broken link removed**
Look to typical applications, comparator with hysteresis.
Reference voltage of the comparator is switched by the positieve feedback
The use of positive feedback introduce hysteresis in the circuit and avoid false triggering as long as the signal perturbation is lower than the hysteresis window.
elec_boy,
A schmitt trigger uses positive feedback to derive its reference voltage as a function of its output state. For example, suppose we have an inverting Schmitt trigger with a reference (inverting) input of voltage of 1 V when the output is in the "1" state. When the input (non-inverting) input exceeds 1 V, the output switches to zero, and the reference, due to positive feedback, changes to 0.9V. The input voltage must now be reduced to a value below 0.9V before the output will switch back to zero. The positive feedback has given you a noise immunity of 0.1V.
Regards,
Kral
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