There has been increasing demand of high-speed internet service over telephone lines in apartment, hotel, and office building, etc. with explosive increase of internet users and diversification of tasks. Previous solutions were not satisfactory in transfer rate of data and length of use. In this work, as a solution of this demand, a high-speed communications system over one-pair telephone line(CPEV) is proposed and analog circuits are designed and implemented.
As the CSMA/CD, the protocol of ethernet physical layer, is half duplex, this system separates Tx and Rx in time domain. This system allows the channel to only one-directional signal, i.e. restrains Tx when Rx is detected, Rx when Tx is detected at both parts of link segment. Therefore, the needed circuits are Rx and Tx amplifiers with perfect switching characteristics, which enable communications over targeted 500 meters. The receiver amplifier recover the digital stream by compensating the high frequency signals attenuated along the long channel, amplifying with high gain, and clipping the amplified signal to have 2Vpp. The transmitter amplifier has a gain of about unity and a bandwidth of from about 100kHz to 15MHz, so produces low distortion to 10Base-T signal of which spectrum concentrates in 5~10MHz.