Pulse or digital communications – Repeaters – Testing
Patent
1989-05-14
1992-04-14
Chin, Stephen
Pulse or digital communications
Repeaters
Testing
333 18, 3647242, H03N 730
Patent
active
051054400
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method for adaptive equalization of pulse signals, particularly bipolar pulse signals, in which a pulse signal is analyzed with regard to its distortion and the result of the analysis controls a variable equalization network with respect to its transmission characteristics.
BACKGROUND ART
In order to ensure during transmission of digital data that the transmission channel, normally having a capacitive component, is not charged up to a d.c. voltage value, the digital data are usually transmitted in an AMI-code or in form of a bipolar (=pseudoternary) pulse train for which the logical characteristic state 0 is represented by the signal voltage +U or -U with alternating polarity, for every successive 1-bit. Thereby, for an alternating sequence of logical 0 and 1 states in the pulse train, there is a smaller signal change or pulse train rate than for directly successive logical 1 states.
Due to the frequency dependent transmission characteristic of data transmission channels, digital pulse signals with different pulse train rates are often distorted during transmission to such a degree that at the end of the transmission path they can no longer be recognized as such. In order to regenerate the digital data, the transmitted digital pulse signals must first of all be equalized before they can be fed to a pulse shaper. For the automatic equalization of the distorted digital signals, generally an adaptive equalizer which automatically adapts its equalization characteristic to the unknown and often variable transmission characteristic of the transmission channel is used. Such an adaptive equalizer essentially consists of the variable and adaptable equalization network and a circuit arrangement controlling the equalization network.
The above discussed type of circuit arrangement for adapting the equalization network of an adaptive equalizer for digital pulse signals is already West German Patent Publication No. 29 08 588. It comprises a predistortion filter, an operational-sign-coincidence-auto correlator, and a correction circuit to guarantee control stability. This known circuit, however, has the disadvantage that it is very complicated in design, due particularly to the use of a sign-coincidence-auto correlator, so that on the one hand it is susceptible to functional errors and on the other hand it is expensive to produce.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a simple and reliable method and apparatus for adaptive equalization of distorted digital pulse signals with different pulse train speeds, particularly for bipolar signals.
This object is achieved according to the invention by the fact that, for the analysis of the pulse signals, the edge time deviations of a signal derived from pulses occurring at the output of the variable equalization network relative to a reference signal are determined and that, depending on the determined edge deviations, individual network parts are enabled or disabled for the purpose of minimization of the edge deviations.
During the transmission of digital pulse signals with changing pulse train speed, particularly bipolar signals, via a transmission channel with frequency dependent transmission characteristics, the pulse edges of the digital signals are time shifted with varying degrees relative to the original signals, which is due to the continuous change of the spectral structure of the pulse signals.
The invention is based on the knowledge that this highly differing shifting of the individual pulse edges of the digital signals indicates the level of distortion of the digital signals and hence can be evaluated for control of the variable transmission network for the purpose of optimizing the degree of equalization.
The method according to the invention is particularly well-suited for the equalization of bipolar pulse signals. As has been already described above, bipolar pulse signals can involve signal changes which vary greatly in amplitude. So, on the one hand, symmetrical bipolar pulse
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Chin Stephen
Gossett Dykema
Nixdorf Computer AG
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