Adaptive equalizer for binary signals and method of operating same

Abstract

An adaptive equalizer for high-speed binary signals, operating in baseband, comprises a transversal filter receiving digitized samples of incoming symbols and feeding them to a decision stage. An error signal derived from the difference between the filtered and the decided samples, for each coefficient of the transversal filter and for each iteration of the processing by that coefficient, is fed to an updating unit, where its sign is compared with the sign of the corresponding filtered sample to determine their identity or disparity. The result is a binary discriminating signal sent to a coefficient calculator and to a threshold generator which receives from that calculator the current coefficient and, dependent on the polarity of that coefficient and on the logical value of the discriminating signal, produces a threshold value to be compared with the absolute magnitude of the error signal. Whenever that absolute magnitude exceeds the existing threshold, it causes the count of an up/down counter to be incremented or decremented, depending on whether the two compared signs are different or equal. Whenever the up count of the down count reaches a predetermined limit in any cycle, the counter resets itself to zero and triggers the calculator to update the existing coefficient, again on the basis of the discriminating signal, by either halving or doubling that coefficient.