Patent ID: 6970515

Claim:
A line driver for coupling a data transceiver to a transmission line having a load impedance Z via a transformer with a turns ratio of 1:n, said data transceiver transmitting signals in a first frequency range and receiving signals in a second frequency range different from said first frequency range, said line driver comprising: an input port for receiving an input signal voltage; an output port for supplying an output signal voltage to said transformer; a differential amplifier having a low pass filter characteristic, coupled with said input port, for amplifying said input signal voltage and outputting an amplified signal voltage; termination resistors for coupling said amplified signal voltage therethrough as the output signal voltage to said output port, said termination resistors having a resistance R t , where R t = Z 2 â¢ â¢ n 2 Ã— k â¢ â¢ ( 0 < k â‰¤ 1 ) ; and a positive feedback path for coupling said output signal voltage from said output port to an appropriate node of said differential amplifier so that a synthesized output impedance substantially matches the load impedance Z over the second frequency range, wherein said positive feedback path includes a resistive coupling if the second frequency range is lower than the first frequency range, and said positive feedback path includes a capacitive coupling if the second frequency range is higher than the first frequency range.