A synthetic impedance telecommunication line driver has no electrical
energy-dissipating elements in series with its output, and synthesizes
its output impedance in accordance with current fed back from an output
current (mirror) sensing circuit. This allows the driver to realize
substantially reduced power requirements for driving a telecommunication
line, such as, but not limited to a DSX-1 line. The driver includes an
operational amplifier having a first polarity input coupled through an
input resistor to an input port, to which a signal voltage to applied to
an output port is coupled. A second polarity input of the amplifier is
coupled to a reference voltage. A feedback resistor is coupled between
the amplifier output and its inverting input. An output current-dependent
current source, such as a current mirror coupled in circuit with the
output node, generates a current as a small fraction k of the output
current. This mirrored fraction of the output current is fed back to an
input of the amplifier, and enables the output impedance Zout of the
driver to be defined in terms of the mirror current ratio k and the value
of the driver amplifier's feedback resistor.