Equalization Design for a 600 MBd Quantized Feedback PCM Repeater

A frequency domain approach to the design of equalization for a quantized feedback PCM repeater is described. The method commences with a feedback path specified as a low-pass filter function and path delay from which the ideal signal path equalization is calculated. This characteristic is approximated by network realizable poles and zeros, with all-pass sections satisfying the non-minimum phase equalization requirement, and gives designs no more complicated than for conventional systems. Examples of equalizers for high attenuation coaxial cable transmission systems are given. Consideration is given to factors which influence the partitioning of the equalization between signal and feedback paths which result in a recommendation that the crossover frequency is placed at about one percent of half-baud frequency. Compensation in the feedback path for equalization deviations caused by power separation filter cut-offs in the signal path enables the overall equalization characteristic to be closely approximated in both amplitude and phase over a frequency range of about four decades. Results obtained on an experimental 600 MBd repeater that has been constructed are illustrated.