Microprocessors require digital inputs. Thus, where a microprocessor
is used as part of a control system, the analogue output from a sensor has
to be converted into a digital form before it can be used as an input to the
microprocessor. Thus there is a need for an analogue-to-digital
converter (ADC). Analogue-to-digital conversion involves a number of
stages. The first stage is to take samples of the analogue signal (Figure
1.38(a)).