A passive echo cancellation circuit for reducing echoes on a subscriber
line includes an output driver adapted to drive a downstream signal on
the subscriber line. First sensing circuitry is coupled to the output
driver and adapted to sense a current on the subscriber line to generate
a first voltage. A balancing network is adapted to receive at least a
portion of the downstream signal. Second sensing circuitry is adapted to
sense a current in the portion of the downstream signal passing through
the balancing network to generate a second voltage. An upstream driver is
adapted to subtract the second voltage from the first voltage to generate
an upstream signal. A method for canceling echoes on a subscriber line
includes driving a downstream signal on the subscriber line; sensing a
current on the subscriber line to generate a first voltage; providing a
portion of the downstream signal to a balancing network; sensing a
current in the portion of the downstream signal passing through the
balancing network to generate a second voltage; and subtracting the
second voltage from the first voltage to generate an upstream signal.