Online Safety Checking for Delay Locked Loops via Embedded Phase Error Monitor

Abstract

In today's automotive ICs, online safety checking is often required in order to achieve a high Automotive Safety Integrity Level (ASIL). For a Delay-Locked Loop (DLL), the most important safety (or health) indicator is the “phase error between the input clock signal and the output clock signal”. In this paper, we present a phase error monitoring scheme for DLLs, using circuits made of only standard cells. The proposed scheme can monitor the phase error continuously to record its worst-case values during a designated monitoring session. As a result, hazardous phase error glitches can be exposed and an alarm can be raised. We have implemented this monitoring scheme for a Delay Lock Loop in a 90 nm CMOS process and post-layout simulation is conducted to verify its effectiveness. Experimental results show that it can help expose hazards induced by dynamic power glitches that occurs within 1ns.