Abstract: A digital system for producing a bipolar rectangular waveform of fixed frequency having a duty cycle proportional to the magnitude of an input digital word is provided to drive a servovalve. The digital word is input to a modulator which outputs a fixed frequency rectangular waveform whose duty cycle varies from 0 to 100% dependent upon the magnitude of the digital word. In order to adapt this output to drive a fail-fixed servovalve in which maximum flow occurs at a predetermined portion of maximum rated current, a scaling network is provided which limits the variation in the duty cycle of the output square wave.