Towards single-chip diversity TMR for automotive applications

Abstract

The continuous requirement to provide safe, low-cost, compact systems makes applications such as automotive more prone to increasing types of faults. This may result in increased system failure rates if not addressed correctly. While some of the faults are not permanent in nature, they can lead to malfunctioning in complex circuits and/or software systems. Moreover, automotive applications have recently adopted the ISO26262 to provide a standard for defining functional safety. One of the recommended schemes to tolerate faults is Triple Modular Redundancy (TMR). However, traditional TMR designs typically consume too much space, power, and money all of which are undesirable for automotive. In addition, common mode faults have always been a concern in TMR which their effects would be increasing in compact systems. Errors such as noise and offset that impact a TMR sensor input can potentially cause common mode failures that lead to an entire system failure. In this paper, we introduce a new architecture and implementation for diverse TMR in a speed measurement system that would serve automotive cost and safety demands. Diversity TMR is achieved on a single chip by designing functionally identical circuits each in a different design domain to reduce the potential of common mode failures. Three versions of a speed sensing application are implemented on a mixed-signal Programmable System on Chip (PSoC) from Cypress Semiconductors. We introduce errors that impact speed sensor signals as defined by the ISO26262 standard to evaluate DTMR. Our testing shows how DTMR can be effective to different types of errors that impact speed sensor signals.