A propagation delay generator is provided for controlling the duration of a bubble generate waveform of a bubble memory system. A first means is responsive to a digital input signal and provides an initializing signal to a current source. A capacitor is charged, responsive to an R-C time constant, by an increased voltage level prompted by the initializing signal. A second means is responsive to the charging signal in excess of that required to charge the capacitor. The second means thereby provides a digital output that is delayed from the digital input signal.