Disclosed is a method and apparatus which facilitates the use of existing
power that is ordinarily unused or discarded to provide power to a telephone interface
circuit when the circuit is in the on-hook state, thereby alleviating the need
to use loop current to power the interface during the on-hook state. Existing clock
signals are used to charge capacitors that are normally used for capacitive coupling
of digital data across the high voltage isolation barrier. Although only small-value
capacitors are needed for transmitting data across the capacitive interface, larger-value
capacitors are used and are configured to form a charge pump to generate power
to the interface at all times. Thus the interface always has a steady source of
power available for use, including during the on-hook state for powering circuitry
that can detect, modulate, and transmit on-hook signals across the capacitive interface.
