Wave Shaping

Pulse Stretcher

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.