Analogue-To-Digital Converter

Analogue-To-Digital Converter or ADC, an electronic device for converting data from analogue to digital form for use in electronic equipment such as digital computers, digital audio and video recorders, and communications equipment.

The conversion of analogue data to digital form is now fundamental for all sorts of everyday processes. Many phenomena in the physical world, for example the intensity and colour of light or the intensity of sound waves, vary in a continuous or analogue manner. Previously, the recording, transmission, and manipulation of images and sound were executed by transforming the images and sound into electrical voltages, whose variations exactly mimicked changes in the original quantity. These continuously varying electrical voltages were, in turn, manipulated in various ways before being converted back to their original form. With the development in the power of computers, however, it has become more convenient and economical to convert these analogue signals to digital form for the purposes of recording, transmission, and alteration, and then convert them back to analogue form for their final use. A further advantage of the digital transmission and manipulation of signals is that it can, to a large extent, prevent the introduction of distortion and noise into the signal when it is transmitted and copied.

The process of analogue-to-digital conversion has two main stages. The first is the “sampling” of the continuously varying electrical waveform. In this context, sampling means measuring the voltage of the signal at an extremely rapid fixed rate; in the case of music, for example, the rate is usually 44.1 kHz (that is 44,100 times per second). The range that these measurements cover is taken to be divided into a number of integral increments or steps; in the case of music it is usually 65,534. In the second stage, called “quantization”, the nearest of these integral values to the actual value is assigned to represent the sampled value. The minute discrepancy between the actual value of the measurement of the voltage and the integral value used is called “quantization error”, and would be perceptible if it were not largely eliminated by a further electronic process. Sampling and quantization are usually done in the order just described for sound-recording purposes, but for use in television and video recording they are done in the reverse order inside the analogue-to-digital converter. The final stage of the conversion is to express the integral number as a binary digital number. A series of such digital numbers is output by the converter, representing the digital form of the signal that was input. All these processes are usually carried out within a single integrated chip.