An analog-to-digital converter (abbreviated ADC, A/D or A to D) is a device which converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement. The reverse operation is performed by a digital-to-analog converter (DAC).
Typically, an ADC is an electronic device that converts an input analog voltage or current to a digital number proportional to the magnitude of the voltage or current. However, some non-electronic or only partially electronic devices, such as rotary encoders, can also be considered ADCs.
The digital output may use different coding schemes. Typically the digital output will be a two’s complement binary number that is proportional to the input, but there are other possibilities. An encoder, for example, might output a Gray code.