Pulse or digital communications – Multilevel – Bipolar signal
Reexamination Certificate
2000-02-18
2001-02-06
Chin, Stephen (Department: 2734)
Pulse or digital communications
Multilevel
Bipolar signal
C375S229000, C375S230000, C375S232000, C375S233000, C333S018000, C333S02800T
Reexamination Certificate
active
06185262
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for suppressing disturbances in a bipolar data stream in the case of large line lengths. The signals of the data stream are fed to a coarse adjustment and a fine adjustment in an equalizer and to a downstream level detector. From there they are fed back to the equalizer from the level detector via a control device. The invention also relates to a circuit configuration for carrying out the method.
Particularly in the case of stringent requirements on range for the reception of ISDN data, problems can arise in intersymbol interference, modulation of the amplitudes by power supply interference sources, interference from high-frequency sources and direct crosstalk from neighboring transmission lines. In addition, continuous operation without interruption of reception requires a low bit error rate (1E-7) and is therefore exposed to the full temperature response over its entire operating time. Moreover, the relevant standards permit variations in transmitted amplitude of up to 50% and a bit rate variation of +/−13%. At the same time, there is a requirement for the automatic capability to adapt to arbitrary cable lengths within the specified ranges. Depending on cable type, for example, in the T1 standard these can be between 0 and 2000 meters or between 0 and 2800 meters.
Since the signal-to-noise ratio worsens continually with increasing length of the transmission link, ever more stringent requirements have to be placed on the equalizer and/or the equalizer itself produces bit errors because of constant corrections in continuous operation.
It has been known to date to transmit and evaluate at the start of transmission standard signals which serve as training pulses or reference pulses. Such a method and the associated arrangements are described by T. Suzulei et al. in the article “Line Equalizer for a Digital Subscriber Loop Employing Switched Capacitor Technology”; IEEE Transactions on Communications, Vol. COM-30, No. 9, September 1982, pp. 2074-82. Such an arrangement is also known from U.S. Pat. No. 4,768,205.
Methods are also used which require a perpetually continuous correction, or which render restrictions necessary with regard to the amplitude variation and the tolerated noise.
Furthermore, methods are known which work with a multiplicity of detection levels and/or fixed detection levels. A method in which fixed detection levels are used for regulation is described by G. J. Smolka et al. in the article “A 384-kbit/s ISDN Burst Transceiver”; IEEE Journal of Solid State Circuits, Vol. SC-22, No. 6, December 1987, pp. 1004-10. It is disadvantageous in these last-mentioned methods that erroneous settings cannot be prevented in some circumstances, depending on the technology used. Moreover, the outlay on circuitry rises very sharply for longer ranges. Furthermore, in such cases the influence of pulsed interference sources or individual interference events is seen very clearly on the receiving path of the equalizer, and they lead to bit errors.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method and a device for suppressing disturbances in a bipolar data stream which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which permit acceptable reception, although they are exposed to a multiplicity of interference sources, and which nevertheless ensure a fine reception balance which is of sufficiently fine resolution in conjunction with an immediate reaction upon violation of absolute interference limits.
With the above and other objects in view there is provided, in accordance with the invention, a method of suppressing disturbances in a bipolar data stream transmitted through a long transmission line. The method comprises the following method steps:
subjecting a disturbed, bipolar data stream to one of a coarse and fine adjustment in an equalizer;
subsequently comparing the data stream with three reference levels in a level detector;
forming a signal in case of a level violation of a reference level;
sampling the signal in the level detector with a measuring clock pulse to form a digital sampled signal and supplying the digital sampled signal to a control device;
stochastically evaluating the level violation represented by the sampled signal in the control device, and setting the equalizer with the control device as a function of the result of the evaluation, the setting comprising the following:
coarsely setting the equalizer when a percentage number of level transgressions of a lower reference level undershoots a first lower decision threshold or when a percentage number of level transgressions of an upper reference level overshoots a first upper decision threshold; and
finely setting the equalizer when the percentage number of level transgressions of the upper reference level undershoots the first upper decision threshold or when the percentage number of level transgressions of the lower reference level overshoots the first lower decision threshold.
In accordance with an added feature of the invention, the equalizer is not set with the control device and it is considering adjusted when the percentage number of level transgressions of the middle reference level corresponds with the percentage number of level transgressions prescribed by a second upper decision threshold and a second lower decision threshold.
In accordance with an additional feature of the invention, there is provided a step of stochastically evaluating, with a tendency controller influencing the control device, the level violations represented by the sampled signal and, as a function thereof, changing the decision thresholds, prescribed in the control device, for the purpose of regulation such that coarse or fine settings of the equalizer lead to an adjustment.
In accordance with another feature of the invention, the signal formed by violations of the reference levels is undersampled with a measuring clock pulse.
In accordance with a further feature of the invention, the measuring clock pulse corresponds to three times a clock pulse length of a sequence of 18 binary signals.
In accordance with again an added feature of the invention, the third reference level is defined between the upper reference level and the lower reference level such that a level spacing of D=F+S is observed, wherein S represents a sum of all disturbances to be taken into account, F represents the fine setting range of the equalizer, and F and S are fixed as
F
2
+
S
=
A
2
to form a control range A=c−a of the equalizer.
In accordance with again an additional feature of the invention, the percentage-prescribable number of violations of the upper reference level and lower reference level is set as a function of a prescribed amplitude variation of the data stream.
In accordance with again another feature of the invention, after concluding the fine setting of the equalizer, the middle reference level in the control device is replaced by a data stream produced from the data stream output by the equalizer with the aid of a voltage peak detector and a downstream receiver.
With the above and other objects in view there is also provided, in accordance with the invention, a circuit configuration for performing the above-outlined method. The novel circuit includes:
an equalizer having an automatic gain controller for fine setting and a filter for coarse setting of a signal amplitude;
a level detector connected to the equalizer via a signal line;
a control device connected to the level detector via lines, the control device controlling the equalizer via a line;
a tendency controller for influencing the fine setting and coarse setting connected to the control device via a bidirectional line; and
a voltage peak detector connected to the equalizer and a receiver connected to the voltage peak detector and to the control device, the voltage peak detector and the receiver processing a data stream received from the equalizer via the signal line, feeding b
Chin Stephen
Ghayour Mohammad
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
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