Patent ID: 7532043

Claim:
A system for driving a transmission line pair with a selected one of a plurality of differential input signals, the apparatus comprising: a crosspoint switch circuit that includes a plurality of inputs that are arranged to receive the plurality of differential input signals, wherein the crosspoint switch circuit is arranged to couple the selected one of the plurality of differential input signals to a first pair of input terminals; a redundant crosspoint switch circuit that includes a plurality of inputs that are arranged to receive the plurality of differential input signals, wherein the redundant crosspoint switch circuit is arranged to couple the selected one of the plurality of differential input signals to a second pair of input terminals; a multiplexer circuit that is arranged to selectively couple one of the first pair of input terminals and the second pair of input terminals to a first node and a second node, respectively, in response to a multiplexer control (MX_CTL) signal; a line driver circuit that includes an amplifier circuit and a signal detector circuit, wherein the amplifier circuit includes a differential input terminal and a differential output terminal, wherein the differential input terminal is coupled to across the first node and the second node, and wherein the differential output terminal is coupled to the transmission line pair at a third node and a fourth node, wherein the signal detector circuit is coupled to the differential input terminal across the first node and the second node, wherein the signal detector circuit is arranged to assert a signal detection (SD) signal at a first logic level when an valid signal is identified at the differential input terminal, and wherein the signal detector circuit is arranged to assert the signal detection (SD) signal at a second logic level when an invalid signal is identified at the differential input terminal, wherein the line driver circuit is arranged such that the line driver circuit is enabled when an enable (EN) signal is asserted and disabled when the enable (EN) signal is de-asserted; and a controller circuit that is arranged to monitor the signal detection (SD) signal from the line driver circuit, wherein the controller circuit is externally located with respect to the line driver circuit, and wherein the controller circuit is arranged to selectively control the enable (EN) signal for the line driver circuit and the multiplexer control (MX_CTL) signal in response to the signal detection (SD) signal from the signal detector circuit.