Quantized Feedback in an Experimental 280-Mb/s Digital Repeater for Coaxial Transmission

A 280-Mb/s digital coaxial repeater employing two-level transmission with quantized feedback for dc-wander control has been designed and constructed. The linear channel forward path includes a 10-MHz low-frequency cutoff, and the missing low frequencies are supplied by a filtered signal from the repeater output. This approach effectively removes dc wander without use of code restriction, making it possible to use two-level rather than three-level transmission without loss of information transmission. Eye margins are consequently significantly greater than for previously designed 280-Mb/s three-level repeaters. The bandwidth ratio, or ratio of upper to lower 3-dB down points of the signal transmission path, is only 10 for this approach compared to several hundred for the three-level bipolar approach (and more for codes with higher transmission efficiency). This results in greatly reduced susceptibility to interference from lightning and power surges, elimination of preamplifier overload, and simplified repeater design.