Single chip pulse-width modulator based on a compressed look-up table

Reference waveforms for three-phase pulse-width modulation (PWM) circuits are normally retained in ROM. The authors describe a novel technique based on the second forward difference for compressing the reference information into a simple logic circuit. A complete PWM circuit containing two look-up tables is implemented in a single-chip programmable device. A significant reduction in gate count results with a semicustom implementation. A novel Fourier-based simulation technique which can detect the nonharmonic spectral components generated by asynchronous PWM is described. The technique offers a simpler solution than complex analytical methods based on double Fourier integration and fast Fourier analysis. Simulated results, with an accuracy of -75 dB, compared favorably with the practical results obtained from the single-chip circuit