Digital loop extension using mid span amplification

A simple negative impedance amplifier has been developed that can bidirectionally amplify a wideband signal on a telephone line. The amplifier uses a multibranch RC network to accurately match the negative impedance to the characteristic impedance of the line over a wide range of frequencies. An operating range extension of 1 km has been achieved which gives an increase of 40% in area coverage. Advantages of this amplifier are low complexity and good tolerance to component variation. A 2 wire/4 wire amplifier has also been developed. It has achieved a range increase of 1.5 km which is 27% more range or 61% more area coverage. The amplifier can also operate closer to either end of the line than a negative impedance amplifier of the same gain. A disadvantage of the 2w/4w amplifier is the increase in circuit complexity by approximately a factor of four. These techniques are not dependent on the modulation scheme and thus a single unit could be used in ADSL, HDSL, or BR-ISDN loops