A pulse width modulator (PWM) generates the binary data from an analog signal. It has a analog signal input and another input for a ramp generator. The PWM basically consists of a voltage comparator the compares the ramp and input signals. The binary output is given by:
<math> v_{out} = \left\{ \begin{array} 1, & v_s > v_{ramp} \\
0, & v_s < v_{ramp} \end{array} </math>