A Current-Mode Trigger Pulse Generator for Fast Coincidence Circuits

The design and philosophy of a new current-mode trigger pulse generator are described. The pulse generator uses two transistors in a coupled emitter configuration and only ordinary components. The output impedance at collectors is 93 ohms though this may be reduced where it is desired to match other transmission line impedances. Rise time is less than 3 nanoseconds with jitter in the 10-11 second range. Pulse output is ±2.5 volts and extremely clean and square with little undershoot or overshoot. Pulse length may be chosen, in the normal way, to be from ~10 nsec. up to microseconds. The circuit may be retriggered as soon as the output has recovered to zero. Its layout will be discussed and also its use as a replacement for limiter circuits in fast coincidence measurements.