Q.What is a Digital to Analog convertor?

A digital-to-analog converter (DAC) turns a binary number into a proportional analog output voltage. Each bit of the digital input is given a weight according to its place value, and the DAC adds these weighted contributions so that the output is an analog voltage representing the code. Two op-amp-based designs are standard.

The binary-weighted resistance DAC applies each bit through a resistor whose value is scaled by powers of two — $R, 2R, 4R, 8R, \dots$ for successively less significant bits — into the inverting node of a summing amplifier. Because each resistor sets a weight $R_f/R_n$, the most significant bit contributes the most current and the least significant bit the least, so the summed output is proportional to the binary value. It is simple in principle but needs many different, precisely-matched resistor values, which is hard to achieve for many bits. …