Companding D/A and A/D converters

The companding of digital-to-analog converters (DAC) and analog-to-digital converters (ADC) is discussed. Phenomena which exhibit a logarithmic characteristic are reviewed, such as current flowing through a forward-biased silicon junction that doubles for an increase in forward voltage of 18 mV. The duality existing between logarithmic systems and linear systems is explained, and companding principles are presented, including the mu law and the A law. Functions and applications of companding DACs and ADCs are also discussed, and it is shown that 8-bit companding DACs and ADCs provide a cost effective and convenient method of achieving the accuracy and dynamic range of criteria of a majority of real-world interfaces without incurring problems associated with longer-bit formats.