A comparator is an electronic device that compares two voltages or currents and outputs a digital signal indicating which is larger. It has two analog input terminals and one binary digital output. Comparators are often used to check whether an input has reached some predetermined value. They are commonly used in devices that measure and digitize analog signals, such as successive-approximation ADCs and relaxation oscillators. There are two basic types of voltage comparator: inverting and non-inverting. In an inverting comparator, the input signal is applied to the inverting terminal and the reference voltage is at the non-inverting terminal. This creates a positive voltage output if the input voltage is less than the reference voltage. In a non-inverting comparator, the input signal is applied to the non-inverting terminal and the reference voltage is at the inverting terminal. This creates a positive voltage output if the input voltage is greater than the reference voltage. A comparator consists of a high gain differential amplifier whose output is compatible with the logic gates used in the digital circuit. The gain is high enough that a very small difference between the input voltages will saturate the output, and the output voltage will be in either the low logic voltage band or the high logic voltage band of the gate input.