1.  Field of the Invention
The digital pulse width modulator (DPWM) is a device which allows creation of an output, a designated frequency and pulse width, and further allows the varying of the pulse width (on-time) of frequency of the waveform. 
Typically, the device is set up at one frequency, and on-time of the waveform is made larger or smaller or left alone to produce the desired effect. 
Applications for this device in microprocessor circuits are:
1.  voice synthesis where the output pulse width is low pass filtered to produce an analog waveform.  The larger the pulse width, the larger the analog voltage at the output of the low pass filter; the smaller the pulse width, the smaller the analog voltage at the output of the low pass filter.  PA1 2.  a vacuum fluorescent power supply.  Here the output pulse width drives a transistor which drives current through a coil, so the larger the pulse width, the higher the current and the higher the voltage generated.  The smaller the pulse width, the smaller the current, and the smaller the voltage generated. 
2.  Prior Art
Examples of pulse width modulators are described in the following U.S. Patents:
U.S. Pat.  No.  4,386,311 to Michael P. Bafaro; "Dual Slope Pulse Width Modulation Regulator And Control System"; discloses a dual slope pulse width modulation regulator for separate control of two independently operative power supplies. 
U.S. Pat.  No.  4,353,115 to Ray Ruble et al.; " Apparatus For Synthesizing A Sinusoidal Output"; discloses a sinusoidal synthesizer which produces a sinusoidal AC power output from a modulated pulse train.  A pulse width modulator is used in the control of an output voltage in combination with a high gain negative feedback signal. 
U.S. Pat.  No.  4,105,939 to Charles H. Culbertson; "Direct Digital Technique For Generating An AC Waveform"; discloses the generation of a three-phase pulse width modulated output for driving the power stages with a rod control mechanism in a nuclear reactor facility. 
U.S. Pat.  No.  4,099,109 to Alberto Abbondanti; "Digital Apparatus For Synthesizing Pulse Width Modulated WaveForms And Digital Pulse Width Modulated Control System"; discloses an induction motor driver with adjustable speeds which responds to stored pulse width modulated waveforms which represent predetermined patterns of output voltage levels. 
U.S. Pat.  No.  4,072,206 to Gerald L. Larson et al.; " Device For Regulating Vehicle Road Speed"; utilizes a control pulse width for each mile per hour vehicle speed variation about a set speed. 
U.S. Pat.  No.  4,065,765 to Peter B. Wagner; "Pulse-Width Demodulator And Information Storage Device"; discloses a device to convert a pulse width modulated word into a digital format. 
U.S. Pat.  No.  4,001,728 to Wolfger Schneider; "Digital Method Of Pulse Width Modulation"; discloses a method of encoding the information in a pulse width modulated signal.