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. Most are sensitive to the shape of event waveforms and may require cumbersome delay lines. The authors describe a zero crossing discriminator which accurately detects the maxima and minima of a measured waveform. Basically, it consists of a fast voltage comparator and a single integrating time constant, RC. A time walk of 100 ps in an amplitude range exceeding 100:1 has been achieved for waveforms from 1.5 ns to 15 ns full width at half maximum (FWHM). An arming level discriminator is added to eliminate triggering by noise. Easily implemented in either monolithic of 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.<>