A Digital-to-Analog Converter or DAC takes a
multi-bit digital input and converts it to an analog voltage. The
anlaog voltage is proportional to the value of the number.
The most common form of DAC works by adding together a set of binary
weighted currents. Each bit of the incoming binary number controls a
switch that either includes or exclude the relevant current from the
sum. The basic output is then a current that is proportional to the
binary number. This is called a current output DAC.
If we take the current output fo the DAC and feed it to a
trans-resistance amplifier then we generate an output voltage
proportional to the current and so to the original number. This is
called a voltage output DAC.
An N-bit DAC produces 2N different output voltages. For a unipolar DAC these usually range from 0V to some maximum Vmax. In this case, if the incoming number is m then the output voltage is
Various different conventions allow DACs to produce bipolar (both positive and negative) output voltages.