A comparator as name says, it compares a signal on one input of an op-amp with a known voltage called the reference voltage on the other input .comparator is nothing but an open loop op-amp with two analog inputs (differential input ) and one digital output (signal ended output).
The op-amp has very large gain used in open loop. Hence the output may be in positive or negative saturation voltage depending upon which input is larger .Op-amp is perfectly suited for comparator application because of its high input impedance and large open loop gain.
The important characteristic of comparator are
- Speed of operation
- Compatibility of output
1. Speed of operation
The output of comparator must switch rapidly between the saturation level (+vsat or -Vsat) and also respond instantly to any change of condition at its input .it says that bandwidth of op-amp should be very high because wider bandwidth ,higher is the speed of operation .
It is smallest amount of difference voltage required at the inputs of comparator to make the output change its state .It is measured in mv. The accuracy depends on voltage gain ,common -mode rejection ratio (CMRR), input offset voltage and thermal drifts .
3. Compatibility of output
The comparator is a form of analog to digital converter ,its output must swing between two logic levels suitable for a certain logic family such as transistors -transistor logic (TTL).