Comparator exhibits temporary hysteresis

摘要

Noise and interference can be significant problems when you transform a signal from a sine wave to a square wave. When the sine wave crosses the reference level, a comparator can exhibit uncertainty, or jitter. A common method to eliminatecomparator uncertainty is to introduce positive feedback by using a resistor divider at the comparator's output. The drawback of this method is that the resulting hysteresis produces an offset that's a function of the state of the comparator. With anasymmetric output, the offset of the comparator's input is also asymmetric. The result is asymmetry in the desired rectangular output signal. You can eliminate this drawback by creating a "temporary-hysteresis" characteristic. You create thischaracteristic by substituting a capacitor for one of the positive-feedback resistors, as in Figure 1.