A PRECISION TIMING DISCRIMINATOR FOR HIGH-DENSITY DETECTOR SYSTEMS

Most high resolution time measurement techniques require discriminators that accurately mark the time arrival of events regardless of their intensity. Constant fraction discriminators or zero-crossing discriminators are generally used. We describe a zero-crossing discriminator that accurately determines the peak of a quasi-Gaussian waveform by differentiating it and detecting the resulting zero-crossing. Basically, it consists of a fast voltage comparator and two integrating networks: an RC section and an LR section used in a way that keeps the input impedance purely resistive. A time walk of 100 ps in an amplitude range exceeding 100:1 has been achieved for wave-forms from 1.5 ns to 15 ns FWHM. An arming level discriminator is added to eliminate triggering by noise. Easily implemented in either monolithic or hybrid technology, the circuit is suitable for large multichannel detector systems where size and power dissipation are crucial. Circuit diagrams and typical measured data are also presented.