Studies on subscriber line equalizer using decision feedback equalizing circuit
Norio Tamaki · Electronics and Communications in Japan (Part I Communications) · 1989
Abstract The metallic subscriber line is composed of the cascade connection of cables with different core radius and the openended branch line called bridge‐tap. Previously, the line equalizer for such a line has been constructed by combining the f equalizer, which has the equalization function for the single core cable, and the DFE circuit. The DFE circuit has a structure suited to LSI implementation, but has a problem in that a decision error propagates to succeeding bits, since the result of the decision is fed back as the compensation waveform for the intersymbol interference. This paper proposes a line equalizer based on the DFE circuit, which includes the DFE pre‐equalizer to stabilize the DFE circuit. The design principle is presented. More precisely, the error propagation in the DFE circuit is analyzed. Combined with the analysis of the subscriber line characteristics, the required characteristics for the DFE equalizer are shown. Then a discussion is made on the number of taps in the DFE circuit, which determines the scale of the DFE circuit. Finally, a design example is presented for 320 kbit/s TCM transmission‐line equalizer based on the design method presented. By experiment, the desired characteristics are verified.