Image Number 18 for United States Patent #4519083.
A digital data transmission system for transmitting digital data from digital data handling hardware over a transmission line by analog signal representation and for receiving analog signal representation for reception of digital signals by the digital data handling hardware, incorporates an integrated circuit PSK modem. The modem has a transmitter which includes an encoder for encoding digital data into a first format for conversion to corresponding PSK signals and a transmitter modulator, implemented in switched capacitor circuits, for phase modulating a first carrier frequency according to the first format. The modem has a receiver that includes a demodulator, implemented in switched capacitor circuits, for demodulating PSK signals on a second carrier frequency to provide a second format for conversion to corresponding digital signals, and an encoder for encoding the second format into corresponding digital signals. In the preferred embodiment, the transmitter includes a buffer for the accommodation of a variety of modem protocols, a first filter for compensation of gain distortion in the transmission line, and a second filter for compensation of phase distortion in the transmission line. In this preferred embodiment, the receiver includes compensating filters for transmission line gain and phase distortion, automatic gain control and adaptive equalization filtering for reducing cross-talk noise between the transmission and receiving lines.