A dedicated voltage comparator will generally be faster than an operational amplifier for general use put into operation as a comparator. A dedicated voltage comparator can also contain additional functions such as a precise internal voltage reference, an adjustable hysteresis and a clock input.
A dedicated voltage comparison chip, such as LM339, is designed to interfere with a digital logic interface (on a TTL or CMOS). The output is a binary state often used to interface between real-world signals and digital circuits (see analog-to-digital converter). If there is a fixed voltage source, for example, from an adjustable DC device in the signal path, a comparator is the equivalent of a cascade of amplifiers.
When the voltages are nearly equal, the output voltage will not fall on one of the logical levels, so analog signals will enter the digital field with unpredictable results. To make this interval as short as possible, the amplifier cascade is a big gain.
The circuit consists mainly of bipolar transistors. For very high frequencies, the input impedance of the stages is low. This reduces the saturation of the bipolar transistors at slow and high junction, which otherwise would entail long periods of recovery. Small Schottky diodes, like those of the binary logic models, improve the performance, although the performance remains the same as the circuits of the amplifiers using analog signals.
The drop rate does not make sense for these devices. For ADC flash applications, the eight-port distributed signal corresponds to the voltage and current gain after each amplifier and the resistors act as level switches.
LM339 does this with an open collector output. When the inverter input is at a higher voltage than the non-inverting input, the comparator output is connected to the negative supply.
When the non-inversion input is greater than the inverted input, the output is “floating” (it has a very high impedance on the ground). The gain of the operational amplifier as a comparator is given by this equation V (out) = V (in).
