A single wire data bus or connector couples a handset (terminal) to a headset (accessory) and conveys DC power from the handset to the headset. Low threshold PMOS switch 619 replaces the conventional diode and is switched off to prevent storage capacitor discharge when the bus is pulled low by either the headset or handset. The conventional diode (418, figure 4) distorted the microphone signal and caused the microphone signal to vary in amplitude as the DC current through it changed. Because the switch impedance is low the resistance of Rserial can be raised, thereby increasing the output of the condenser microphone. The intrinsic diode 620 of the PMOS switch acts as a start-up device. The switch may be a bipolar transistor.
