Substrate switching noise analysis and layout/circuit considerations in monolithic power converters

A monolithic power converter has the analog control circuit and the switching power stage integrated on the same silicon die. The noise generated by the switching power stage can affect the sensitive analog circuits through the shared common substrate and degrade the system performance. Although much literature has been published about the substrate noise generated by digital circuits in mixed-signal systems, the analysis methods and results may not apply for monolithic power converters. Monolithic power converters use different process technologies, have much higher noise peak voltages, and have noise that is synchronized to the pulse-width modulator (PWM) switching period. To handle strong switching noise that exists in monolithic power converters, analysis of the sources of the switching noise, the noise paths, and the noise effects on analog circuitry is necessary. The noise effects on the PWM control circuit are explained in this paper, and a circuit and layout design guide helps to improve the substrate switching noise immunity. The experimental results show the noise immunity improvements.