While negative feedback tends to keep amplifiers within their linear region, positive feedback forces them into saturation. 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. An often-effective solution is to use positive feedback to introduce a small amount of hysteresis.
Noisy signals can occur in any application, and especially in industrial environments.
As the signal crosses the threshold region, the noise is amplified by the open loop gain, causing the output to briefly bounce back and forth. This is unacceptable in most applications, but it can generally be cured by introducing hysteresis. Noise causes multiple transitions. Where to use hysteresis Besides comparator noise reduction, system hysteresis is used in on-off control to avoid overly frequent cycling of pumps, furnaces and motors. In the simplest applications a controller turns an actuator on and off as a system parameter falls below or rises above a reference set point.