High Resolution Zero‐Crossing Detector for Long Crossover Times

A circuit designed to detect the zero‐crossing of bipolar pulses having crossover times of 100 nsec or greater is described. True zero‐crossing detection is accomplished by using an external strobe to generate a pedestal which is then applied to a tunnel diode, normally biased off, allowing it to switch when the input signal crosses zero. Tests with scintillation pulses show that amplitude‐dependent timing errors are less than 0.25 nsec for a pulse‐height range of 100. The principal application of the circuit is in the separation of scintillation pulses according to their pulse shapes.