A CMOS delay locked loop and sub-nanosecond time-to-digital converter chip

Phase-locked loops have been employed in the past to obtain sub-nanosecond time resolution in high energy physics and nuclear science applications. An alternative solution based on a delay-locked loop (DLL) is described. This solution allows for a very high level of integration yet still offers resolution in the sub-nanosecond regime. Two variations on this solution are outlined. A novel phase detector, based on the Muller C-element, is used to implement a charge pump where the injected charge approaches zero as the loop approaches lock on the leading edge of an input clock reference. This greatly reduces timing jitter. In the second variation the loop locks to both the leading and trailing clock edges. In this second implementation, software coded layout generators are used to automatically layout a highly integrated, multichannel time-to-digital converter (TDC) targeted for one specific frequency. The two circuits, DLL and TDC, are implemented in CMOS 1.2 mu m and 0.8 mu m technologies, respectively. Test results show a timing jitter of less than 30 ps for the DLL circuit and less than 190 ps integral and differential non-linearity for the TDC circuit.