A device/circuit/IC that converts a continuous analogue signal into a discrete binary signal. There are many forms of ADC, including continuous balance converters, voltage-to-frequency converters, and dual ramp or integrating converters. A simple continuous balance converter is shown in the diagram. The counter is initially set to zero so that signal V₂ from the digital-to-analogue converter (DAC) section of the circuit is zero. When the unknown input V₁ is greater than V₂, the comparator provides an output voltage that opens the gate and allows pulses to be applied to the counter. So long as the gate remains open, clock pulses are fed to the counter and V₂ continues to increase. When V₂ equals V₁, the comparator output falls to zero and closes the gate. This ‘freezes’ the number stored in the counter, which can then be displayed on a digital readout device. In practical forms of the device, the counter is one that can count ‘up’ and ‘down’ to allow changes in V₁ to be followed.

4-bit analogue-to-digital converter