An adaptive line equalizer LSI for ISDN subscriber loops

An adaptive line equalizer LSI applied to a time-compression multiplexing transmission system, which transfers 320-kb/s AMI coded signals to provide the 144-kb/s (2B+D) transmission capacity recommended by CCITT, is described. The square root f equalizer can adaptively equalize up to 53-dB cable loss at Nyquist frequency (160 kHz), using switched-capacitor filter (SCF) technology. The equalizer transfer function is optimized in the time domain. The coarse automatic gain control circuit is composed of a fourth-order SCF. A high-speed operational amplifier, with wide output voltage swing and excellent stability against load capacitance variation, has been developed. The equalizer enables 5.5-km transmission over 0.5-mm diameter cable with two bridged taps because of its wide gain dynamic range and the use of decision feedback. A small chip size, 6.2*6.6 mm, and low power consumption, 80 mW (from a 5-V single supply), are achieved in 3- mu m CMOS technology.<
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