4 Channel Codec Filter `SICOFI®-4´

A highly programmable four channel Codec Filter Chip for analog telephone subscriber lines is presented in this paper. As a great benefit for the user, but also a great challenge for the analog circuitry, the chip works with a single 5 Volt power supply and is fabricated in a 1¿ CMOS technology. The circuit includes digital signal processing for filtering in the receive and transmit paths, impedance matching and transhybrid balancing filters, special hardware filter structures for decimation and interpolation at higher sampling rates and AD/DA converters. The circuit can easily be adapted to different country standards by different coefficient sets.