Implementation of a digitally controlled SiC CMOS PWM generator using a tunable current-starved delay generator for high-temperature switched-mode regulators

This paper describes the design of a SiC pulse width modulation (PWM) signal generator in the HiTSiC® CMOS process from Raytheon Systems Limited. The high-temperature applications of the circuit include motor control in heavy equipment, deep earth drilling, dc-dc voltage converters and power inverters. The results presented in this paper are for the PWM circuit operating with an input clock frequency of 100 kHz and a supply voltage range of 12 to 15 V. The building blocks for the PWM include a current-starved delay generator, a comparator and XNOR gates. The delay is controlled by a 6-bit binary input that allows the user to dynamically tune the duty cycle. Experimental results show the circuit to have a tunable duty cycle between 16.3% and 84.3% at 400°C.