Switched hybrid circuit for use with digital subscriber lines

Abstract

The present invention provides a switched impedance matching network which may be implemented in a hybrid circuit of a digital subscriber line (DSL) system, or in any other wire-bound communications system for which two-wire-to-four-wire conversion, and vice versa, must be accomplished. In accordance with the preferred embodiment of the present invention, the matching network comprises switchable circuit modules of discrete-valued resistor and capacitor components. Preferably, the circuit modules are assembled into an array of buffered first-order RC circuits. The buffers comprise amplifiers that are switched on or off to control the switching of the circuit modules. The buffer amplifiers also isolate the individual circuit modules from each other and eliminate the need to implement transmission switches between the modules. The switching of the buffer amplifiers clears or blocks the transmission paths between the individual modules, thereby providing the optimum path through the module array. By controlling the transmission paths through the circuit module array, the balancing impedance of the matching network is optimized to match the impedance of the subscriber line in use, thus maximizing transhybrid loss and minimizing near-end echo.