Introduction
Window comparators, or limit comparators as they are sometimes called, determine when the input voltage is within a pre-selected range. The output voltage usually goes to a TTL high when the input voltage is within the pre-selected range. A typical window comparator circuit normally consists of two comparators with two reference adjustments: one for the low trip level, and one for the high trip level. If the reference voltages are derived from the same resistor divider string, hystersis can not be added without having the trip levels interact. If the reference voltages are independently derived they can drift in different directions causing the window to widen or possibly disappear.