Absolute-value comparator touts accuracy, size

摘要

A typical window comparator uses two comparators and a single op amp to determine whether a voltage is inside or outside a boundary region. Figure 1 shows a typical implementation. IC_1 is an inverting op amp with a gain of -1. V_(REF) and -V_(REF) create the window limits. When V_(IN) becomes more positive than V_(REF), the output of IC_(2A) goes low. When V_(IN) becomes more negative than -V_(REF), the output of IC_(2B) goes low. If V_(IN) is lower than V_(REF) and greater than -V_(REF), both outputs of IC_2 remain high. The LM319 and AD548 come in 14- and eight-pin DIPs, respec- tively. The LM319 accommodates sepa-rate input and output power sup- plies. The input supply can be +- 15V referenced to analog ground, and the output can use a logic supply referenced to logic ground. The circuit's input limit is +-2.5V because of the maximum differential-input limit of the LM319. If you think the input will exceed a +-5V differential: voltage between V_(REF) and V_(IN) or -V_(REF) and V_(IN), then you must incorporate a clamping network with many additional discrete components. The circuit in Figure 2 qvercomes these limitations.