Abstract: An equaliser circuit arrangement for compensating for the frequency-dependent characteristics of a transmission line such as an untwisted pair, for lines of lengths up to, say, 125 meters and at data rates up to, say, 155MBits/sec., in which signals from the transmission line are applied by way of a unity gain path and a frequency-selective path including a first wide-band amplifier of variable gain to a summing node. The signals at the summing node may be further amplified by a second wide-band variable gain amplifier using gain control signals derived for the first amplifier.

Abstract: An equalisation arrangement compensates for multipath phase and amplitude distortion effects in a transmission channel by first measuring such distortion effects as they occur over time in a calibration phase, thereby obtaining phase and amplitude compensation factors, then applying these factors to a correcting circuit situated in the signal path of the receiver at the appropriate times during a subsequent data transmission phase. Calibration is achieved by feeding a received calibration signal to an amplifier, preferably a successive detection logarithmic amplifier (26), comparing the phase of the limited linear output of the logarithmic amplifier with a delayed version of itself (30, 28), and using the amplitude information (39) in the logarithmic output (72) of the logarithmic amplifier (26) and the phase-change information (35) resulting from the phase comparison to compute the phase and amplitude compensation coefficients.