Single-Chip Adaptive Transversal Filter IC Employing Switched Capacitor Technology

Development of compact, high-speed, and low power adaptive transversal filters (ATF´s) has been of great interest. Such ATF´s have already been successfully fabricated in monolithic form employing a short channel MOSFET process and switched capacitor technique, using only complete analog circuit technology while eliminating inherent analog problems. This IC with five taps works with both ±5 V and 10 V supplies at a clock rate of more than 250 kHz. It has been designed for multipurpose applications such as a decision feedback equalizer (DFE), echo canceller (EC), and linear equalizer (LE), the last of which has already been reported [5]. The architecture to realize these applications will be described first. Much discussion is presented on the investigation of the operation, characteristics, and performance limitations of this IC in the DFE mode, from which those in the EC mode for two-wire full-duplex data transmission can be understood. For a single echo with magnitude of one half that of the original signal and delay time of one clock period from the original signal, and convergence factor of 0.2 for weight adaptation, the DFE operating at the clock rate of 100 kHz completes equalization within about 1.2 ms resulting in a residual rms distortion of -45.4 dB. The dominant performance limitation factors are found to be both the correlator harmonic distortion and transversal filter noise, but not the convolver harmonic distortion which is the dominant factor for the LE.