Evaluating the impact of substrate noise on conducted EMI in automotive microcontrollers

Board-level I/Os signal integrity and conducted EMI have become a critical concern for high-speed circuit and package designers, and a major element of performance and reliability degradation in modern electronic systems, in particular for automotive microcontrollers, which must satisfy stringent low-EMI and noise immunity requirements. One of the most detrimental root causes of I/O signals conducted EMI is the simultaneous switching noise generated by the toggling I/Os (SSO) on the power distribution network of the I/O ring. However, this is not the only noise source that must be considered. In fact, an often overlooked contributor to SSO is the noise generated by the switching digital core that propagates to the I/Os and the noise-sensitive on-chip analog circuitry throughout the common silicon substrate. In this work, we analyze the impact of substrate noise on the I/O signals conducted EMI of an industrial automotive microcontroller, and we compare it against other noise sources. Moreover, we demonstrate the effectiveness of the technological protections against substrate noise in a leading-edge technology.