Comparator with unilateral hysteresis

Normally, a comparator has inherent hysteresis, that is, when the Input voltage rises, the comparator will react only when the reference voltage is exceeded by a certain amount. When the inputvoltage drops, the comparator changes state only when that voltage is weIl below the reference potential. Hysteresis is essential to prevent a system clattertng or vibrating around its reference Ievel.