An analog-to-digital converter (ADC) measures an analog input and produces a digital code representing that measurement.

The conversion combines two distinct operations: the signal is sampled at a particular time, and the measured amplitude is quantized to one of finitely many codes.

For an ideal $N$-bit converter with input span $V_{range}$, one code step is approximately

$$\Delta V=\frac{V_{range}}{2^N}.$$

The converter cannot distinguish voltage differences much smaller than one code step, and inputs outside its allowed range can clip or damage the input circuitry depending on the hardware.

Practical ADCs also have acquisition and conversion time. The signal source must settle sufficiently during the sampling interval, and the sampling rate must be appropriate for how quickly the underlying signal can change.

An ADC therefore turns a physical voltage into a finite-resolution sequence of measurements whose timing and range are part of the measurement model.