Development of a CMOS integrated zero-crossing discriminator using analog continuous-time division

High resolution time spectroscopy experiments require circuit techniques that accurately mark the time arrival of events regardless of their amplitude. For this purpose zero-crossing techniques are generally used because of their independence of the signal amplitude. Since the output response of real voltage comparators is related to the input signal slope and overdrive, even these time-pickoff methods are degraded by an amplitude dependent time walk. Therefore a new time-pickoff circuit is proposed using analog continuous-time division to eliminate the undesired amplitude information. Based on a standard CMOS technology a first test version has been developed that is presently under production. First promising SPICE simulations using the simulation parameters of an unexpensive 1.2 μm CMOS technology have shown a time walk fairly below 200 ps (FWHM) over a 40 dB amplitude range and for input signal risetimes of 2 to 3 ns