EP0645066A1 - Circuit d'asservissement en frequence a courant continu pour limiteur a seuil de donnees de ginomy - Google Patents

Circuit d'asservissement en frequence a courant continu pour limiteur a seuil de donnees de ginomy

Info

Publication number
EP0645066A1
EP0645066A1 EP93913331A EP93913331A EP0645066A1 EP 0645066 A1 EP0645066 A1 EP 0645066A1 EP 93913331 A EP93913331 A EP 93913331A EP 93913331 A EP93913331 A EP 93913331A EP 0645066 A1 EP0645066 A1 EP 0645066A1
Authority
EP
European Patent Office
Prior art keywords
signal
threshold level
control signal
data
change
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP93913331A
Other languages
German (de)
English (en)
Inventor
David James Mccabe
Stephen Akira Williams
Graham Edgar Beesley
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lucent Technologies Wireless Ltd
Original Assignee
AT&T Wireless Communications Products Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by AT&T Wireless Communications Products Ltd filed Critical AT&T Wireless Communications Products Ltd
Publication of EP0645066A1 publication Critical patent/EP0645066A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/06—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
    • H04L25/061—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset
    • H04L25/065—Binary decisions
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/06—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
    • H04L25/061—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset
    • H04L25/062—Setting decision thresholds using feedforward techniques only

Definitions

  • This invention relates to a system for data recovery and in particular to a system for extracting binary data from an analogue signal containing such data .
  • Such systems are utilised, for example, in digital communications systems in which digital data is transmitted, which data is a mixture of digitised analogue information and control data, such as synchronising data.
  • data has to be recovered from the demodulated signal which is, of course, an analogue signal.
  • An example of a transceiver which could utilise such a system is described in our European patent application 0333419 which is incorporated herein by this reference.
  • the demodulated signal which is output from the frequency discriminator is filtered, and then passed to a data recovery circuit in the form of a data slicer before being applied as digital data to a data processor.
  • the present invention is essentially concerned with data recovery circuits of this and similar type, although we do not wish to be limited to the particular arrangement shown in EP 0333419, which is presented simply by way of example, for the purpose of explanation.
  • the fundamental purpose of a data recovery circuit is to decide what the smoothly varying analogue input signal represents m binary terms.
  • the circuit element which carries out such a task is the comparator but because in this application the signal is constantly crossing and recrossing the threshold level as the 1 's and O ' s of the data are received, the comparator is often referred to as a slicer.
  • the slicer is thus the basic component of the data recovery circuit, and its output is a binary signal representing either 0 or 1. More complex systems are known, but the simple slicer system is quite effective.
  • the problem with the slicer system is choice of the optimum slicer threshold level.
  • the threshold level must be able to vary in order to quickly adjust to a freshly acquired signal; on the other hand, the threshold level must not be forgotten too quickly in the event that the input signal fades, or becomes unreliable.
  • the slicer input or output signals may be filtered and thence used to generate a variable threshold level based on a reasonable estimate of the centre of the input signal. This works well provided that the data comprises a reasonably balanced mixture of O ' s and 1 's .
  • the philosophy adopted for the present invention is that a workable threshold value should be quickly acquired when the input signal first appears, but that the rate of change of threshold value should be slowed down when the extracted data is positively indicated as already being good or is expected to be of inadequate quality to permit changes.
  • the invention provides means for measuring the signal strength and for altering the rate of change of the threshold level in accordance with this measurement. In particular, rapid changes in the threshold level will only take place if the signal strength is not below a predetermined critical value.
  • means are additionally provided for detecting whether the system is in synchronism, for example frame lock acquisition, and for altering the rate of change of the threshold in accordance with this decision.
  • rapid changes of threshold level will be allowed.
  • the advantage of the prevention of rapid tracking, provided synchronism is achieved, is that any short duration interference does not alter the threshold level.
  • the measured signal strength is high then the incoming signal should be good and worth rapidly tracking; however, if synchronism has been achieved, there is no longer any need for rapid tracking of the threshold level as the data is now about good enough and any further refinement of the optimum threshold level can be allowed relatively slowly.
  • a represen ⁇ tative transceiver is shown under reference 1.
  • This transceiver may, for example, be of the type described in our European patent application 0333419.
  • the transceiver includes means (not shown) for measuring the received signal strength of the incoming signal, and providing a logic signal at a "Low RSSI" terminal 2 which is high when the RSSI (received signal strength indicator) signal lies below some predetermined threshold, but is otherwise low.
  • the transceiver further includes means (also not shown) for identifying, by bit pattern match, when the synchronising words have been received correctly, and providing a logic signal at a "Frame Sync" terminal 3 which is high when a bit pattern match has shown that the sync words have been received correctly. This is all known technology, and will not be described further.
  • the demodulated data from the receiver portion of the transceiver is output at a "Demod data" terminal 4 and comprises an analogue waveform such as shown under reference 5.
  • This signal is applied to one input of a slicer circuit 6 in the form of a comparator.
  • the output from the slicer 6 takes the form of a digital waveform such as shown under reference 7.
  • a threshold level which is adjusted by means of a low pass filter feedback network 9 to follow the variations in the input waveform 5.
  • the slicer operates to compare the incoming analogue signal with the threshold level to thereby produce the digital waveform 7 in the known manner.
  • the threshold level is adjusted to sit between the upper and lower levels of the input waveform and follows the variation of optimum slicing level quickly so that good data is not lost, but when the incoming data is bad the threshold level varies slowly as the signal knowledge is inadequate to optimally select the threshold level.
  • the illustrated circuit utilises the "low RSSI" and "Frame Sync" signals described above to control the time constant of the feedback network 9 so that only when the RSSI shows an adequate level of signal and the system has not detected adequate synchronism are fast threshold level changes permitted.
  • the terminals 2 and 3 are connected to respective inputs of a NOR gate 10.
  • the output of the NOR gate is applied as a control input 11 to the feedback network 9.
  • the feedback network 9 includes a low-pass filter comprising a timing capacitor C, a high value resistor R1 and a low value resistor R2.
  • a switch S selectively places the resistor R2 in parallel with resistor R1 to thus lower the time constant of the filter.
  • Switch S is an electronic switch under the control of the signal at input 11.
  • the input 12 of the low pass filter is taken from the input waveform at terminal 4 of the transceiver 1.
  • the output 13 of the low pass filter is passed to the threshold level input 8 of the slicer 6-
  • the switch S has a third position in which input 12 is, in effect, isolated.
  • This switch position may be used, for example, during the transmit portion of alternate transmission/reception cycles such as are used in certain communications systems. In such systems transmission and reception alternate on a cyclic basis; during transmission, if the switch S is switched to the third position, it will hold the threshold level from the previous reception window, and this level will be used to commence slicing in the next reception window. In practice, the switch S will be switched to the third position and back to the first/second position on a cyclic basis to match the alternations of reception and transmission.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Dc Digital Transmission (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

Dans un émetteur-récepteur (1) faisant partie d'un système de communication numérique, un système de collecte des données à partir du signal analogique démodulé comprend un circuit limiteur à seuil (6) pour extraire les données numériques du signal analogique et un filtre passe-bas (9) pour produire à partir du signal analogique d'entrée (5) un signal de seuil destiné au circuit limiteur à seuil (6). Le filtre passe-bas (9) a une constante de temps variable, choisie par un commutateur (5) pour modifier la rapidité de changement du niveau de seuil conformément à la position du commutateur. Le commutateur lui-même est commandé par un signal de commande composite (16) qui est fourni par une porte (10) et qui est indicatif de deux propriétés du signal RF reçu, en l'occurence l'intensité du signal reçu et l'état de la synchronisation. L'agencement est conçu de manière à ce qu'une rapidité élevée du changement du niveau du seuil soit permise uniquement lorsque l'émetteur-récepteur n'est pas synchronisé e^_t^_ que l'intensité du signal reçu est au-dessus d'un niveau prédéterminé.
EP93913331A 1992-06-10 1993-06-09 Circuit d'asservissement en frequence a courant continu pour limiteur a seuil de donnees de ginomy Withdrawn EP0645066A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9212263 1992-06-10
GB929212263A GB9212263D0 (en) 1992-06-10 1992-06-10 System for data recovery
PCT/GB1993/001226 WO1993026110A1 (fr) 1992-06-10 1993-06-09 Circuit d'asservissement en frequence a courant continu pour limiteur a seuil de donnees de ginomy

Publications (1)

Publication Number Publication Date
EP0645066A1 true EP0645066A1 (fr) 1995-03-29

Family

ID=10716826

Family Applications (1)

Application Number Title Priority Date Filing Date
EP93913331A Withdrawn EP0645066A1 (fr) 1992-06-10 1993-06-09 Circuit d'asservissement en frequence a courant continu pour limiteur a seuil de donnees de ginomy

Country Status (4)

Country Link
EP (1) EP0645066A1 (fr)
AU (1) AU4344393A (fr)
GB (2) GB9212263D0 (fr)
WO (1) WO1993026110A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5872468A (en) * 1997-06-12 1999-02-16 Northern Telecom Limited Level detector circuit, interface and method for interpreting and processing multi-level signals
GB2333214A (en) * 1998-01-09 1999-07-14 Mitel Semiconductor Ltd Data slicer
WO2003034674A1 (fr) * 2001-10-10 2003-04-24 Telefonaktiebolaget Lm Ericsson (Publ) Recepteur a seuil de detection adaptatif pour communications amrt
CN103516366B (zh) * 2013-09-26 2017-01-18 中科院微电子研究所昆山分所 输入信号强度指示器及指示方法
JP6626362B2 (ja) * 2016-02-19 2019-12-25 アズビル株式会社 フィルタ時定数変更回路およびｄ／ａ変換回路

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2462073A1 (fr) * 1979-07-17 1981-02-06 Thomson Csf Procede et dispositif pour l'extraction de donnees numeriques en presence de bruit et de distorsions
US4821292A (en) * 1987-06-03 1989-04-11 General Electric Company Adaptive limiter/detector which changes time constant upon detection of dotting pattern
US5148449A (en) * 1989-05-26 1992-09-15 Motorola, Inc. Centering multi-level data

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9326110A1 *

Also Published As

Publication number Publication date
GB2282942B (en) 1996-01-24
AU4344393A (en) 1994-01-04
WO1993026110A1 (fr) 1993-12-23
GB9212263D0 (en) 1992-07-22
GB9425397D0 (en) 1995-02-15
GB2282942A (en) 1995-04-19

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