Digital implementation of a transmit line build-out circuit for the DSX-1 interface

The design of an all-digital DS-1 transmit line build-out circuit (LBO) is reported. The application of the LBO is to compensate for the length variations ranging from 0 m to 200 m of the 22 American Wire Gauge (AWG) twisted pair cable between a DS-1 line card and the DSX-1 cross-connect. At the cross-connect, the signal must fit into the North American DSX-1 standard pulse-shape mask. The present approach generated a distorted DS-1 pulse digitally from samples stored in a ROM. The numerical samples are passed to a digital-to-analog converter to generate the bipolar DS-1 signal. To meet the DSX-1 standard, it was sufficient to synthesize the pulse from eight stored samples, each 5 b wide (for 32 quantization levels). Two versions of the distorted DS-1 pulse, corresponding to two LB settings, were needed to satisfy the DSX-1 standard, valid for the range 0 m to 132 m and 66 m to 215 m, respectively