DSU/OCU.

This paper summarizes the development of LSIs for DSU/OCU equipment which provide 2-way digital subscriber loop transmission over existing twisted pair cable using a time compression multiplexing technique. Emphasis is placed on the LT (Line Termination)-LSI, which performs the major functions necessary to achieve accurate bit-by-bit transmission, such as equalization of ROOT f characteristics, equalization of impairments caused by bridged taps, timing recovery, and bipolar coding/decoding. The development can be categorized into two different approaches, one employing an RC active filter for the ROOT f equalizer, and the other employing a switched capacitor filter for the same function. In both approaches, the chip also contains a decision feedback type bridged tap equalizer and timing extraction circuit.