An adaptive SC line equalizer system for four-wire full-duplex and multirate digital transmission

An adaptive switched capacitor (SC) line equalizer system that can be applied to four-wire full-duplex and multirate digital transmission is described. Several kinds of noises can exist in programmable high-gain SC equalizers, such as switching noise, DC offset jump, and transient response. To avoid their effects, an adaptive SC filter is proposed. Two identical SC circuits are used in parallel. An input signal is fed into both SC circuits, and output signals from both circuits are alternately sent after the above noises are eliminated. Furthermore, many different data rates can be handled by slightly modifying an equalizer circuit. A bridged-tap echo canceller and a DC offset canceller are modified so as to be applied to the proposed adaptive SC filter. A line equalizer system, that handles data rates ranging from 3.2 to 64 kb/s was designed. An LSI was fabricated using a 3-μn CMOS process. Experimental results show that noise effects are mostly eliminated, and frequency responses and eye openings are close to the designed values