Pulse Selector

The circuit presented here can be useful in triggering, test and measurement applications. It converts a rising edge into a square pulse whose length is equal to the period of an input pulse train.In the quiescent state, flip-flop IC1B is clear, holding flipflop IC1A set.A TTL-level rising edge at the SELECT input causes a brief spike to appear at the output of gate IC2D. The spike is only a few nanoseconds long, and depends on the propagation delay through NAND gates IC2A, IC2B and IC2C, which are connected as inverters.