FR2474260A1 - REPEATER FOR A DIGITAL TRANSMISSION SYSTEM AND, IN PARTICULAR, METHOD AND CIRCUIT FOR EQUALIZATION USED IN THIS REPEATER - Google Patents

Abstract

RECEIVER FOR SYSTEM FOR THE TRANSMISSION OF DIGITAL SIGNALS BY CABLE, OF THE TYPE INCLUDING A FIXED EQUALIZATION SECTION 13 AND AN ADAPTIVE EQUALIZATION SECTION 12 CONTROLLED BY AN ADJUSTMENT LOOP 10, 11 FROM THE PEAK LEVEL OF THE OUTPUT PULSES TO A VALUE OF REFERENCE (EYE HEIGHT). ACCORDING TO THE INVENTION, A SECOND FEEDBACK LOOP OPTIMIZES THE OPERATION OF THE REPEATER FOR DIFFERENT CHARACTERISTICS OR TYPES OF CABLE DEPENDING ON THE ENERGY AT LOW FREQUENCY OF THE EYE DIAGRAM. THE EQUALIZED SIGNALS ARE TRANSMITTED TO A SECOND PEAK DETECTOR 21 VIA A LOW PASS FILTER TO PROVIDE A TUNING SIGNAL OF A VARIABLE IMPEDANCE 22 MODIFYING THE RESPONSE OF THE EQUALIZATION SECTION 13. APPLICATION TO THE EQUALIZATION SYSTEMS. DIGITAL TRANSMISSION ON PULSE AND CODING MODULATION LINES.

Description

The present invention relates to repeaters for

  digital transmission in pulse modulation and coding and, more particularly, devices intended to compensate

  in these the transmission characteristics of the line.

  Conventional automatic line distortion compensation circuits (line correctors) provide variable equalization by means of a primary equalization control loop to correct the mainly frequency dependent losses due to line length variations. However, changes in the type of cable (eg paper, plastic insulated, etc.), cable characteristics, and signal level changes also affect the operation of the repeaters. The use of extremely effective online codes, such as those known as 4B3T and disclosed in U.S. Patent No. 3,611,141, October 5, 1971, requires precise equalization of online losses, particularly at the lowest frequencies. o this code contains more energy than codes such as those known as HDB3

  (Bipolar High Density 3), whether the signals are scrambled or not.

  A known equalizer design for modula-

  by strongly multiplexed pulses and coding, for example 48

  2.37 megabit per second channels is shown in Figure 1.

  This design includes a primary equalization control loop to keep the height of said "eye pattern" constant, the circuit being carefully designed to provide proper equalization for a range of different line lengths. The equalized signal is taken from a decision point X and applied to a peak detector 10, which measures the peak or "height" of the eye diagram. This

  peak value is amplified and applied to a diode array 11.

  The output of the network 11 is used to control the equalization circuit.

tion.

  During the manufacture of the repeaters is included in the circuit 12 a manually adjustable variable resistor to allow the repeater, once installed, to be set for low content

frequency of the eye diagram.

  One of the objects of the present invention is to provide an improved device in a repeater for a pulse-code modulation digital transmission system to compensate for

  the transmission characteristics of the line.

  One of the features of the present invention is the provision of a repeater for a digital line transmission system comprising a line corrector circuit having an appropriate primary equalization control loop, and an equalizer circuit coupled to the input of the correction circuit having at least one secondary control loop coupled to the output of the correction circuit, said secondary loop comprising a filter coupled to the output of the correcting circuit and a first peak detector coupled to the output of the filter to produce a signal of command that will order means to

  adjustable impedance belonging to the equalizer circuit.

  In a preferred embodiment, the filter of the loop

secondary is a low-pass filter.

  Another feature of the present invention is that it

  provides an equalization method for a digital transponder trans-

  mission on the lines consisting firstly in filtering the digital signals and then in detecting the peak values of the filtered digital signals, finally in deriving from said values of the peak signals a signal

  command that will control the equalization in the repeater.

  The invention will be better understood on reading the description

  detailed below, made by way of non-limiting example, with reference to the appended figures which represent:

  FIG. 1, a block diagram of the equalization device

  tion of the prior art described in the first paragraphs of the foregoing;

  FIG. 2, a block diagram of an equalizing device

  Repeater application applying the principles of the present invention.

  The repeater of FIG. 2 is basically the same as that of FIG. 1, to which the secondary feedback loop has been added. Equalized signals from decision point X are

  applied to a low-pass filter 20 followed by a peak detector 21.

  The output of the peak detector 21 is amplified and applied as a control signal to a variable impedance 22 in the equalizer 13. The low pass filter 20 ensures that the secondary loop responds only to the low frequency content of the diagram. of the eye for the control of the equalizer 13. This automatic control of the equalizer 13 optimizes the equalization for the best diagram of the eye without taking into account the

  type of cable or the characteristic of the input cable.

  It is obvious that the foregoing description has been

  only as a non-limitative example and that other variants may be

  be considered without departing from the scope of the invention.

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Claims (7)

  A repeater for a digital transmission system on lines, characterized in that it comprises a line correction circuit having a suitable primary feedback loop, and an equalizer circuit coupled to the input of said correcting circuit having minus a secondary feedback loop coupled to the output of said correcting circuit, said secondary loop comprising a filter coupled to said output of said correcting circuit and a first peak detector coupled to the output of said filter to produce a control signal which will drive adjustable impedance means of said circuit equalizer.   2. Repeater according to claim 1, characterized by the   said filter is a low-pass filter.   3. Repeater according to claim 1 or 2, characterized in that said primary loop comprises a second peak detector coupled to said output of said correction circuit, and a diode connected between the output of said second detector and said correction circuit for order it.   4. Equation method for a repeater in a digital transmission system on the lines, characterized in that it comprises the following steps: - filtering the digital signals; detecting the peak values of said filtered digital signals; deriving from said peak values a signal of   control for controlling the equalization in said repeater.   5. Method according to claim 4, characterized in that said filtering step comprises filtering by a filter   low pass of said digital signals.   6. Feedback loop for an equalization circuit in a repeater of a digital transmission system on the lines, characterized in that it comprises a filter coupled to the output of said circuit, and a coupled peak detector at the output of said filter to produce a control signal which will control an impedance   adjustable belonging to said circuit.   7. Feedback loop according to claim 6,   characterized in that said filter is a low-pass filter.