FIG. 1 illustrates a transceiver 100 that transmits and receives signals on a twisted pair (TP) 110. The transceiver 100 may be associated, for example, with a local area network (LAN) or a digital subscriber loop (xDSL). The main sources of crosstalk in such a transceiver 100 are usually near-end crosstalk (NEXT), echo crosstalk and far end crosstalk (FEXT). Each transceiver, such as the transceiver 100, transmits a first signal, V1, and receives a different signal, V2, on the same twisted pair 110. V1 corresponds to the transmitted signal generated by the transceiver 100. V2 corresponds to the received signal generated by a second transceiver 120. Since the transceiver 100 knows the transmitted signal, V1, that it has generated, the transceiver 100 employs a “hybrid component” to subtract the transmitted signal, V1, from the voltage (V1+V2) on the twisted pair (TP) 110, to obtain the voltage corresponding to the received signal V2.
Near-end crosstalk results from transmitting and receiving different signals on different twisted pairs 110 and having a signal on one twisted pair interfering with the signal on another twisted pair. Echo crosstalk, on the other hand, is the result of crosstalk on the same twisted pair 110 and of discontinuous impedances along a given path, for example, at each connector. When the transceiver 100 transmits a signal, V1, each impedance discontinuity along the path causes the transceiver 100 to receive a wave or echo back. Thus, a transceiver typically includes a near end cross-talk and echo canceller 200, discussed further below in conjunction with FIG. 2, to address the near end cross-talk and echo cross-talk and to improve the recovery of the transmitted signal.
Conventional cross-talk cancellers must consider the same signal on a given twisted pair multiple times in order to reduce the echo on the same twisted pair, as well as the near end cross-talk on each of the other twisted pairs. For example, in the case of four twisted pairs, there is a factor-of-four redundancy, since a given signal is used once for the echo cancellation on the same twisted pair and three additional times for the near end cross-talk on the other three twisted pair. Such redundancies unnecessarily consume circuit area and power. A need therefore exists for a cross-talk canceller that reduces the number of redundancies.