Reza Moghimi
Analog Devices

Comparator ICs are designed to compare the voltages that appear at their inputs and to output a voltage representing the sign of the net difference between them. However, even without actual feedback circuitry, capacitive strays from the output to an input (usually the noninverting input), or coupling of output currents into ground (to which the noninverting input is often connected) may cause a comparator circuit to become unstable. Guarding high-impedance nodes and paying careful attention to layout and grounding can help to minimize these coupling effects. Latching is also helpful. But it is not always possible to prevent instability by these measures. This technical paper discusses an often-effective solution, using positive feedback to introduce a small amount of hysteresis.