an electrical circuit and method for generating a continuous train of width modulated pulses . a square wave is generated and a delay circuit provides a delayed analog of the square wave . a controllable duration one - shot multivibrator generates a modulating pulse having a duration proportional to the sum of the absolute value of the modulating signal and a constant offset . the constant offset is chosen so that , in the absence of a modulating signal , the offset provides the largest control signal to the one - shot multivibrator which causes an output modulating pulse from the multivibrator equal in duration to the minimum duration which the multivibrator intrinsically is capable of obtaining . the polarity of the modulating signal is detected , a logical or operation is performed upon the delayed square wave and the modulating pulse and an exclusive or operation is performed upon the combination of the result of the or operation and the polarity detector output logic level .