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.
Comparator
The important characteristic of comparator are
- Speed of operation
- Accuracy
- 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 .
2. Accuracy
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).