WO1994030012A1 - Apparatus for transmission of video information - Google Patents

Apparatus for transmission of video information Download PDF

Info

Publication number
WO1994030012A1
WO1994030012A1 PCT/GB1994/001232 GB9401232W WO9430012A1 WO 1994030012 A1 WO1994030012 A1 WO 1994030012A1 GB 9401232 W GB9401232 W GB 9401232W WO 9430012 A1 WO9430012 A1 WO 9430012A1
Authority
WO
WIPO (PCT)
Prior art keywords
twisted pair
video information
conductors
impedance
matching
Prior art date
Application number
PCT/GB1994/001232
Other languages
French (fr)
Inventor
John Aloysius Mcdermott
Stuart Ogilvy
Original Assignee
John Aloysius Mcdermott
Stuart Ogilvy
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 John Aloysius Mcdermott, Stuart Ogilvy filed Critical John Aloysius Mcdermott
Priority to GB9524784A priority Critical patent/GB2295073A/en
Priority to AU68536/94A priority patent/AU6853694A/en
Publication of WO1994030012A1 publication Critical patent/WO1994030012A1/en

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/10—Adaptations for transmission by electrical cable
    • H04N7/108—Adaptations for transmission by electrical cable the cable being constituted by a pair of wires

Definitions

  • the present invention relates to an apparatus for transmission and reception of video information by twisted pair conductors, particularly although not exclusively for RGB video information signals.
  • balanced inverted and non-inverted signals derived from an output signal from a generator are transmitted through the conductors of a twisted pair thereby to promote immunity to inductive and/or capacitive crosstalk.
  • apparatus for use in the transmission of video information by twisted pair conductors comprising: input means for matching the impedance of a signal source; driving means for respective conductors of a twisted pair including a pair of differential line drivers, one being an inverting amplifier and another a non-inverting amplifier, each amplifier being fed with the signal from the signal source; output means for matching the impedance of the twisted pair conductors; input means for matching the impedance of the twisted pair conductors; driving means for an input of a signal receiver including a differential amplifier, each amplifier input being fed by a respective conductor of the twisted pair; and output means for matching the impedance of the signal receiver, whereby the signals are balanced to promote immunity against inductive and/or capacitive interference.
  • the input impedance matching means of the signal source, and of the twisted pair conductors further include AC coupling means.
  • the AC coupling means is provided by a pair of capacitors.
  • the driving means for the signal receiver includes means for frequency compensation of the video information. Conveniently this is provided by an adjustable filter.
  • the adjustable filter is a capacitive network provided in parallel with the differential amplifier inputs.
  • Figure 1 is a block circuit diagram of a video line driver in accordance with the invention
  • Figure 2 is a circuit diagram showing the transmitter circuit of the line driver of Figure 1
  • Figure 3 is a circuit diagram showing the receiver circuit of the line driver of Figure 1.
  • a video line driver 1 has a transmitter 2, and a receiver 3 connected by three 120 ohm twisted pair cables 5,6 and 7.
  • a video signal source 4 such as a video tape deck is connected to three inputs 13,14 and 15 of the transmitter 2 via three 75 ohm coaxial cables 10,11 and 12 which carry, respectively, red, green and blue baseband signals.
  • An RGB monitor 8 is connected to three outputs 16,17 and 18 of the receiver 3 by three 75 ohm coaxial cables 19,20,21.
  • a BNC jack 30 provides the input connection 14 for a coaxial cable to an input stage 31.
  • the input stage 31 has a resistor 32 to ensure that the impedance of the stage matches that of the cable 11 and a pair of coupling capacitors 33,34 to AC couple the circuit and so block DC from passing further along the signal path into a driver stage 40.
  • the driver stage 40 contains a non inverting amplifier 41 and an inverting amplifier 42 both of which are fed with the signal from the input stage 31.
  • the output of each amplifier 41,42 is connected to a matching circuit 43 which matches the amplifier output impedance of the twisted pair cable 6.
  • the driver stage terminates in an RJ45 jack 44 to which the twisted pair cable 6 is attached.
  • FIG. 3 shows the receiver 3.
  • An input RJ45 jack 51 receives the three twisted pair cables 5,6 and 7.
  • an input stage 50 has a resistor 52 to ensure that the impedance of the stage matches that of the twisted pair cable 6, and a pair of coupling capacitors 53,54 to block DC from passing further along the signal path into the driver stage 60.
  • the driver stage provides selectable frequency compensation by way of capacitor networks 61,62 to the signals before they are passed into the inputs of a differential transformer 63.
  • the output 17 from the amplifier is provided at an output BNC jack 64 having been matched to the characteristic impedance of the 75 ohm coaxial cable 20 by matching circuit 65.
  • the signal is taken from the jack 64 and fed, via the coaxial cable 20 to the green input of the RGB monitor 8 where, in combination with the red and blue input, the video source is displayed.
  • red, green and blue colour baseband signals from the video signal source 4, which could be a video tape deck, are supplied to the inputs 13,14 and 15 of the transmitter 2.
  • Each colour signal is AC coupled, via capacitors 33,34, to the transmitter 2 to prevent earth-loops and to prevent DC components on the transmitter 2 output.
  • an earth loop is disadvantageous as it can introduce hum bars on the final picture display whilst a DC component on the transmitter output will increase resistive energy losses in the cable matching components.
  • the green colour signal for example, is then supplied to the inputs of the non-inverting amplifier 41 and an inverting amplifier 42 to derive two signals of equal magnitude but opposing polarity.
  • the signals carried on the twisted pair conductors must be supplied to a receiver for conversion to a signal capable of being used by a conventional RGB monitor 8.
  • the receiver 3 is, for the reasons given above, AC coupled to the twisted pair and in addition contains circuitry 61,62 adjustable to compensate for the attenuation of high frequency components of the signals caused by the twisted pair conductors themselves.
  • the signals from the twisted pair are then supplied to the inputs of the differential amplifier 63 which produces an output signal capable of being used by a conventional RGB monitor 8.

Abstract

An apparatus (2) for use in the transmission of a video information signal by twisted pair conductors (6), comprises input means (31) for matching the impedance of a video information signal source (4), driving means (40) for respective conductors of a twisted pair (6) including a pair of differential line drivers, one being an inverting amplifier (42) and another a non-inverting amplifier (41), each amplifier (41, 42) being fed with the signal from the signal source (4) output and means (43) for matching the impedance of the twisted pair conductors (6). Signals carried on the twisted pair conductors (6) are thereby balanced to promote immunity against inductive and/or capacitive interference.

Description

APPARATUS FOR TRANSMISSION OF VIDEO INFORMATION
The present invention relates to an apparatus for transmission and reception of video information by twisted pair conductors, particularly although not exclusively for RGB video information signals.
Conventionally video transmission is carried out over 75ohm coaxial cable for all video transmission signals, for example RGB, PAL, CCTV and composite. This impacts negatively on the ability to move the monitor to a new location or to add another, as more dedicated cables are reguired. This increases costs dramatically.
It is accordingly an object of the present invention to provide a novel apparatus for transmission and reception of video information over greater distances and with little or no deterioration in signal quality using twisted pair conductors whilst having advantages in, for example, cost and immunity to interference, over coaxial cables.
In broad concept, according to the present invention balanced inverted and non-inverted signals derived from an output signal from a generator, are transmitted through the conductors of a twisted pair thereby to promote immunity to inductive and/or capacitive crosstalk.
In further accordance with the present invention there is provided apparatus for use in the transmission of video information by twisted pair conductors, comprising: input means for matching the impedance of a signal source; driving means for respective conductors of a twisted pair including a pair of differential line drivers, one being an inverting amplifier and another a non-inverting amplifier, each amplifier being fed with the signal from the signal source; output means for matching the impedance of the twisted pair conductors; input means for matching the impedance of the twisted pair conductors; driving means for an input of a signal receiver including a differential amplifier, each amplifier input being fed by a respective conductor of the twisted pair; and output means for matching the impedance of the signal receiver, whereby the signals are balanced to promote immunity against inductive and/or capacitive interference.
Preferably the input impedance matching means of the signal source, and of the twisted pair conductors, further include AC coupling means. Conveniently the AC coupling means is provided by a pair of capacitors.
It is preferred that the driving means for the signal receiver includes means for frequency compensation of the video information. Conveniently this is provided by an adjustable filter.
It is further preferred that the adjustable filter is a capacitive network provided in parallel with the differential amplifier inputs.
In order to more fully understand the invention, a specific embodiment thereof will be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a block circuit diagram of a video line driver in accordance with the invention,
Figure 2 is a circuit diagram showing the transmitter circuit of the line driver of Figure 1, and
Figure 3 is a circuit diagram showing the receiver circuit of the line driver of Figure 1.
Referring to Figure 1 of the drawings, a video line driver 1 has a transmitter 2, and a receiver 3 connected by three 120 ohm twisted pair cables 5,6 and 7. A video signal source 4 such as a video tape deck is connected to three inputs 13,14 and 15 of the transmitter 2 via three 75 ohm coaxial cables 10,11 and 12 which carry, respectively, red, green and blue baseband signals. An RGB monitor 8 is connected to three outputs 16,17 and 18 of the receiver 3 by three 75 ohm coaxial cables 19,20,21.
In Figure 2 the circuitry relating to the green input to the transmitter 2 will be described, it being understood that the circuitry is identical for all three inputs. A BNC jack 30 provides the input connection 14 for a coaxial cable to an input stage 31. The input stage 31 has a resistor 32 to ensure that the impedance of the stage matches that of the cable 11 and a pair of coupling capacitors 33,34 to AC couple the circuit and so block DC from passing further along the signal path into a driver stage 40. The driver stage 40 contains a non inverting amplifier 41 and an inverting amplifier 42 both of which are fed with the signal from the input stage 31. The output of each amplifier 41,42 is connected to a matching circuit 43 which matches the amplifier output impedance of the twisted pair cable 6. The driver stage terminates in an RJ45 jack 44 to which the twisted pair cable 6 is attached.
Figure 3 shows the receiver 3. An input RJ45 jack 51 receives the three twisted pair cables 5,6 and 7. Referring once more to the green signal, an input stage 50 has a resistor 52 to ensure that the impedance of the stage matches that of the twisted pair cable 6, and a pair of coupling capacitors 53,54 to block DC from passing further along the signal path into the driver stage 60. The driver stage provides selectable frequency compensation by way of capacitor networks 61,62 to the signals before they are passed into the inputs of a differential transformer 63. The output 17 from the amplifier is provided at an output BNC jack 64 having been matched to the characteristic impedance of the 75 ohm coaxial cable 20 by matching circuit 65. The signal is taken from the jack 64 and fed, via the coaxial cable 20 to the green input of the RGB monitor 8 where, in combination with the red and blue input, the video source is displayed.
It will be appreciated that in use, red, green and blue colour baseband signals from the video signal source 4, which could be a video tape deck, are supplied to the inputs 13,14 and 15 of the transmitter 2. Each colour signal is AC coupled, via capacitors 33,34, to the transmitter 2 to prevent earth-loops and to prevent DC components on the transmitter 2 output. It should be noted that an earth loop is disadvantageous as it can introduce hum bars on the final picture display whilst a DC component on the transmitter output will increase resistive energy losses in the cable matching components. The green colour signal, for example, is then supplied to the inputs of the non-inverting amplifier 41 and an inverting amplifier 42 to derive two signals of equal magnitude but opposing polarity. These two signals can then be fed to separate conductors of the twisted pair 6 as a balanced pair of voltages. By balancing the signals carried on the twisted pair, good immunity to capacitive crosstalk is obtained and the twisted pair, through its reduced loop area, provides immunity to inductive crosstalk.
In order that a conventional RGB monitor 8 may be used, the signals carried on the twisted pair conductors must be supplied to a receiver for conversion to a signal capable of being used by a conventional RGB monitor 8. The receiver 3 is, for the reasons given above, AC coupled to the twisted pair and in addition contains circuitry 61,62 adjustable to compensate for the attenuation of high frequency components of the signals caused by the twisted pair conductors themselves. The signals from the twisted pair are then supplied to the inputs of the differential amplifier 63 which produces an output signal capable of being used by a conventional RGB monitor 8.
In tests, transmission distances of up to 100m using twisted pair cables have been obtained with no noticeable loss in picture quality owing to the good immunity of balanced twisted pair conductors to both capacitive and inductive interference.

Claims

CLAIMS :
1. An apparatus for use in the transmission of a video information signal by twisted pair conductors, comprising: input means for matching the impedance of a video information signal source; driving means for respective conductors of a twisted pair including a pair of differential line drivers, one being an inverting amplifier and another a non-inverting amplifier, each amplifier being fed with the signal from the signal source; output means for matching the impedance of the twisted pair conductors; whereby the signals carried on the twisted pair conductors are balanced to promote immunity against inductive and/or capacitive interference.
2. An apparatus for use in the reception of a video information signal carried by twisted pair conductors, comprising: input means for matching the impedance of the twisted pair conductors; driving means for an input of a signal receiver including a differential amplifier, each amplifier input being fed by a respective conductor of the twisted pair carrying the video information signal; and output means for matching the impedance of the signal receiver, whereby the signals carried on the twisted pair conductors are balanced to promote immunity against inductive and/or capacitive interference.
3. An apparatus as claimed in Claim 1 or Claim 2, wherein the input impedance matching means includes AC coupling means.
4. An apparatus as claimed in Claim 3, wherein the AC coupling means is provided by a pair of capacitors.
5. An apparatus as claimed in Claim 3 or Claim 4 as appendant to Claim 2, wherein the driving means for the signal receiver includes means for frequency compensation of the video information.
6. An apparatus as claimed in Claim 5, wherein the frequency compensation means is provided by an adjustable filter.
7. An apparatus as claimed in Claim 6, wherein the adjustable filter is a capacitive network provided in parallel with the differential amplifier inputs.
PCT/GB1994/001232 1993-06-07 1994-06-07 Apparatus for transmission of video information WO1994030012A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB9524784A GB2295073A (en) 1993-06-07 1994-06-07 Apparatus for transmission of video information
AU68536/94A AU6853694A (en) 1993-06-07 1994-06-07 Apparatus for transmission of video information

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9311711.7 1993-06-07
GB939311711A GB9311711D0 (en) 1993-06-07 1993-06-07 Apparatus for transmission of video information

Publications (1)

Publication Number Publication Date
WO1994030012A1 true WO1994030012A1 (en) 1994-12-22

Family

ID=10736759

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1994/001232 WO1994030012A1 (en) 1993-06-07 1994-06-07 Apparatus for transmission of video information

Country Status (3)

Country Link
AU (1) AU6853694A (en)
GB (1) GB9311711D0 (en)
WO (1) WO1994030012A1 (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2350039A (en) * 1999-03-17 2000-11-15 Adder Tech Ltd Transmitting colour video signals via twisted pair lines
WO2005006739A1 (en) * 2003-07-11 2005-01-20 Bang & Olufsen A/S System for wired transmission of signals from a video source to a processing and switching unit
US7206348B2 (en) 1994-01-05 2007-04-17 Avocent Corporation Twisted pair communications line system
US7643018B1 (en) 1994-01-05 2010-01-05 Avocent Corporation Twisted pair communications line system
US8074255B2 (en) 2004-09-28 2011-12-06 Clearcube Technology, Inc. Analog video signal transmission over twisted-pair wires

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108922671B (en) * 2018-06-15 2024-01-23 天瀚科技(吴江)有限公司 Front and rear lens connecting wire of automobile data recorder

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4054910A (en) * 1976-02-26 1977-10-18 Tel-E-Tel, Inc. Communication system for the transmission of closed circuit television over an ordinary pair of wires
JPS6160021A (en) * 1984-08-31 1986-03-27 Fujitsu Ltd Electronic hybrid circuit
WO1993004562A1 (en) * 1991-08-15 1993-03-04 Amulet Electronics Limited Impedance matching

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4054910A (en) * 1976-02-26 1977-10-18 Tel-E-Tel, Inc. Communication system for the transmission of closed circuit television over an ordinary pair of wires
JPS6160021A (en) * 1984-08-31 1986-03-27 Fujitsu Ltd Electronic hybrid circuit
WO1993004562A1 (en) * 1991-08-15 1993-03-04 Amulet Electronics Limited Impedance matching

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
BEEKMANN: "Die Übertragung von Videosignalen auf symmetrischen Leitungen", INTERNATIONALE ELEKTRONISCHE RUNDSCHAU, vol. 29, no. 9, September 1975 (1975-09-01), BERLIN DE, pages 185 - 190 *
PATENT ABSTRACTS OF JAPAN vol. 10, no. 224 (E - 425) 5 August 1986 (1986-08-05) *

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7206348B2 (en) 1994-01-05 2007-04-17 Avocent Corporation Twisted pair communications line system
US7643018B1 (en) 1994-01-05 2010-01-05 Avocent Corporation Twisted pair communications line system
GB2350039A (en) * 1999-03-17 2000-11-15 Adder Tech Ltd Transmitting colour video signals via twisted pair lines
US6618774B1 (en) 1999-03-17 2003-09-09 Adder Technology Ltd. Computer signal transmission system
GB2350039B (en) * 1999-03-17 2004-06-23 Adder Tech Ltd Computer signal transmission system
WO2005006739A1 (en) * 2003-07-11 2005-01-20 Bang & Olufsen A/S System for wired transmission of signals from a video source to a processing and switching unit
US8074255B2 (en) 2004-09-28 2011-12-06 Clearcube Technology, Inc. Analog video signal transmission over twisted-pair wires

Also Published As

Publication number Publication date
GB9311711D0 (en) 1993-07-21
AU6853694A (en) 1995-01-03

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