Total charge theorem for directional couplers and Z-matched coupled lines

It is proven that, in a two-line directional coupler of conventional design, the response to a voltage step on the input is a net amount of coupled charge on the output that is constant, and depends only on fixed properties of the coupler and the size of the voltage step, not on the waveform. This general property of Z-matched coupled lines is useful for pulse creation, and provides insight into certain memory bus techniques that use directional couplers for impedance-matched data transmission.