Digital-to-analog (D/A) converter

A device for converting information in the form of combinations of discrete (usually binary) states or a signal to information in the form of the value or magnitude of some characteristics of a signal, in relation to a standard or reference. Most often, it's a device which has electrical inputs representing a parallel binary number, and an output in the form of voltage or current.

Digital-to-analog (D/A) converters (sometimes called DACs) are used to present the results of digital computation, storage, or transmission, typically for graphical display or for the control of devices that operate with continuously varying quantities. D/A converter circuits are also used in the design of analog-to-digital converters that employ feedback techniques, such as successive approximation and counter-comparator types. In such applications, the D/A converter may not necessarily appear as a separately identifiable entity.

The fundamental circuit of most D/A converters involves a voltage or current reference; a resistive "ladder network" that derives weighted currents or voltages, usually as discrete fractions of the reference; and a set of switches, operated by the digital input, that determines which currents or voltages will be summed to constitute the output.

The output of the D/A converter is proportional to the product of the digital input value and the reference. In many applications, the reference is fixed, and the output bears a fixed proportion to the digital input. In other applications, the reference, as well as the digital input, can vary; a D/A converter that is used in these applications is thus called a multiplying D/A converter. it's principally used for imparting a digitally controlled scale factor, or "gain," to an analog input signal applied at the reference terminal.

Except for the highest resolutions (beyond 18 bits), commercially available D/A converters are generally manufactured in the form of integrated circuits, using bipolar, MOS, and hybrid technologies. A single chip may include just the resistor network and switches; it may also include a reference circuit, output amplifier, and one or more sets of registers (with control logic suitable for direct microprocessor interfacing).

Also see: Digital Filter, Anti-Aliasing, Analog-to-Digital Converter