A comparator is a device that compares two voltages (or currents) and outputs a digital signal indicating which is larger. It has two analog input terminals V+, and V-, and one binary digital output Vo. It is commonly used in devices that measure and digitize analog signals, such as analog-to-digital converters (ADCs).
If the output is digital, then VS+ is H or 1 and VS- is L or 0. It can then be considered to be a one bit analog to digital converter.
A comparator consists of a specialized high-gain differential amplifier. Due to the high gain, Vout is undetermined for the following condition.
\begin{equation} V_- = V_+ \end{equation}A comparator can be implemented using an opamp. The output voltage of the op-amp is given by the equation: \begin{equation} V_{out} = {A_{OL} \, (V_{\!+} - V_{\!-})} \end{equation} where AOL is the open-loop gain of the amplifier.
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