This is a pulse-stretching circuit combined with a conventional NOR diode gate to provide an output pulse of some predetermined minimum duration. It may find application in square-root circuits and with digital oscillators.
With all inputs at ground potential, the output is positive, current flows through capacitor C1 and resistor R1 into the base of transistor Q2, turning it on. Current flows into the base of Q2, until C1 is charged, approximately three times the R1 × C1 constant. If the inputs become positive while Q2 is still conducting, transistor Q1 will not be affected since its base is being held at ground potential by Q2. The inputs regain control of the output when Q2 stops conducting. A diode, D1, in series with R1, provides C1 with a discharge path to ground.