Fast Discriminator with Zero-Crossover

A fast discriminator has been designed to discriminate the pulses from a photomultiplier anode. To match the capabilities of recent electronic circuits dealing with fast pulses in nuclear experiments, a precise time information is extracted from the discriminator using the triggering function of an Esaki-diode. This is done by determining the zero-crossing pint of pulses formed by adding reflected pulses returning from a coaxial cable connected to the input pulses. The performance of the fast discriminator has been examined by use of simulated pulses similar to those from a photomultiplier anode. The time jitter of output pulses is less than 1 ns over the range of input pulse heights between 8 mA and its discriminating point of 0.8 mA. Five outputs are provided of 4 mA in pulse height and about 6 ns in width. Although the output pulses do not have a rectangular form, the rise times at the beginning and the end of the pulses up to 2 mA are about one nanosecond. An attenuator for fast pulses, matching 75 Ω coaxial cables, is also reported.