EP0218703A1 - Systeme de transmission video - Google Patents

Systeme de transmission video

Info

Publication number
EP0218703A1
EP0218703A1 EP19860902755 EP86902755A EP0218703A1 EP 0218703 A1 EP0218703 A1 EP 0218703A1 EP 19860902755 EP19860902755 EP 19860902755 EP 86902755 A EP86902755 A EP 86902755A EP 0218703 A1 EP0218703 A1 EP 0218703A1
Authority
EP
European Patent Office
Prior art keywords
electronic
signal
circuit part
electronic circuit
television system
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.)
Ceased
Application number
EP19860902755
Other languages
German (de)
English (en)
Inventor
Steven Raggett
Thomas Terry
Reginald Swain
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.)
PAYTEL Ltd
Original Assignee
PAYTEL 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 PAYTEL Ltd filed Critical PAYTEL Ltd
Publication of EP0218703A1 publication Critical patent/EP0218703A1/fr
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07F—COIN-FREED OR LIKE APPARATUS
    • G07F17/00—Coin-freed apparatus for hiring articles; Coin-freed facilities or services
    • G07F17/0014—Coin-freed apparatus for hiring articles; Coin-freed facilities or services for vending, access and use of specific services not covered anywhere else in G07F17/00
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/167—Systems rendering the television signal unintelligible and subsequently intelligible
    • H04N7/1675—Providing digital key or authorisation information for generation or regeneration of the scrambling sequence

Definitions

  • the present invention relates to a video transmission system which is preferably particularly applicable to a system for restricting the viewing of received signals to a particular television receiver or to a
  • the viewer in one preferred arrangement being a subscriber to a pay-television service which may be received either by way of a
  • the method and apparatus of the invention provides a modulated video signal which when applied to a standard television receiver produces a scrambled 15 picture, a decoding apparatus bei.ng required to decode the received video signal to produce a proper picture.
  • the method of the invention comprises a method whereby a video signal is transmitted (either alone or impressed on a suitable
  • the invention also includes apparatus for carrying out the aforesaid method.
  • the relevant coded signal may be sent during the field blanking interval, and may be provided in the form of a binary number, which may take the form of a data pulse carrying sub-pulses of various time periods.
  • the coded signal provides a key and the decoder incorporates a lock and the combination of key and lock will allow the signal to be unscrambled.
  • the invention also provides according to a further aspect a security system comprising an electric signal (such as a video signal) including in encoded form, a key number, an electronic decoder apparatus and an electronic circuit part (preferably in the form of a plastic card including electronic components) selectively connectable to the electronic decoder apparatus, the electronic decoder apparatus and the electronic circuit part each including means for carrying out a series of different operations on said key number to produce a desired number from said key number.
  • an electric signal such as a video signal
  • an electronic decoder apparatus and an electronic circuit part preferably in the form of a plastic card including electronic components
  • the electronic signal may comprise a video signal transmitted from a transmitter, the video signal being scrambled, and incorporating a key number, the electronic decoder apparatus and electronic circuit part being provided to subscribers to the television service whereby the desired number produced by the decoding apparatus from said key number may be used to unscramble the scrambled video signal to allow the video signal to be viewed.
  • the scrambling arrangement of the video signal may be changed at regular intervals and the key number changed in synchronism with that.
  • the electronic circuit part may be replaced at regular intervals, for example, weekly, monthly or three monthly.
  • the key number may be included in the electric signal by means of a data pulse, the actual number being encoded in the form of a binary code, the components of the binary code being determined by the width of sub-pulses within the data pulse.
  • the electronic circuit part may incorporate a memory and the data pulse may also incorporate information regarding a particular programme being transmitted so that the electronic circuit part or card can store within its memory information regarding the particular programmes which have been decoded by the decoding apparatus.
  • the video signal may be scrambled by means of inverting the signal values with respect to some of the lines making up the television picture, the inversion being carried out in respect of groups of lines at spaced intervals down the picture.
  • the desired number produced by the decoding apparatus relates to the numbers of the lines which are inverted.
  • the present invention provides a television system in which the video information is scrambled or coded, the video signal including data to provide a key number, decoding apparatus comprising in combination an electronic decoder apparatus and an electronic circuit part, preferably in the form of a plastic card including electronic components, selectively connectable to the electronic decoder apparatus, the electronic decoder apparatus and electronic circuit part each including means for carrying out a series of different operations on said key- number to produce a desired number from said key number, said desired number enabling the decoding apparatus to decode or unscramble the video signal to provide a video signal which may be viewed by a standard television receiver.
  • decoding apparatus comprising in combination an electronic decoder apparatus and an electronic circuit part, preferably in the form of a plastic card including electronic components, selectively connectable to the electronic decoder apparatus, the electronic decoder apparatus and electronic circuit part each including means for carrying out a series of different operations on said key- number to produce a desired number from said key number, said desired number enabling the decoding apparatus to decode or uns
  • the present invention may also provide a method of scrambling a television signal comprising inverting the signals in respect of alternate groups of lines, the groups of lines each comprising a predetermined number of lines, and the television signal containing information relating to the numbers of lines in each group.
  • line inversion of the signal in the above paragraphs we mean changing the value of the composite luminance/chrominance signal so that a black signal becomes white and a white signal becomes black with corresponding changes therebetween and for example blue becomes yellow and vice versa.
  • the decoding apparatus including means whereby, in respect of inverted lines, the composite luminance/chrominance signal is changed into a signal of opposite polarity of corresponding value, (ie +0.5 volt becomes -0.5 volt) and a standard voltage (usually 0.7 volt) is added to that reversed signal.
  • Means may also be provided to compare, after this signal processing, the value of inverted black signal on the inverted lines with the porch signal level and the "standard" voltage value added may be varied so as to determine that the inverted "standard” and porch level are identical.
  • the signal is passed through a variable amplifier in which the gain is varied so as to provide a correct voltage level for inverted white on the inverted lines to provide therefore the required linearity.
  • FIG. 1 is a diagrammatic illustration of the overall method and apparatus of the invention
  • Figure 2 is a perspective view of an encoder , apparatus ,
  • Figure 3 is a perspective view of a decoder and electronic card adjacent a television receiver for showing an unscrambled picture
  • Figure 4 is an enlarged view of the decoder and card apparatus of Figure 3,
  • Figure 5 illustrates the waveform of a normal video signal during the frame blanking interval.
  • Figure 6 illustrates the waveform of a video signal corresponding to part of the video signal of Figure 5 but as modified by apparatus of the invention
  • Figure 7 is an enlarged view of part of Figure 6
  • Figure 8 is a block circuit diagram of the timing and phase lock circuit portion of the encoder
  • FIG 9 is a circuit diagram of the part of the encoder shown in Figure 8,
  • Figure 10 is a block diagram of the video signal path through the encoder
  • FIG 11 is the circuit diagram of the part of the encoder shown in Figure 10,
  • Figure 12 is a block diagram of the timing circuits of the decoder
  • Figure 13 is a circuit diagram of the part of the decoder shown in Figure 12,
  • Figure 14 is a block diagram of another part of the decoder
  • Figure 15 is the circuit diagram of the part of the decoder shown in Figure 14,
  • FIG. 1 there is shown a pay- television system in which a programme produced, for example, in a studio 10 and viewed by a camera 11 produces a video signal which is encoded by an encoder 12 and, after being used to modulate an rf signal is transmitted by a terrestrial transmitter 13 or via a satellite 14 or after modulation by a suitable signal is passed along a cable network 16.
  • the relevant signal is received at the receiving end by an aerial (antenna) 17, dish aerial 18, or cable receiver 19 and the signal is passed to a decoder 21, the decoded signal being " passed to the television receiver 22.
  • the decoder 21 is controlled by means of a card 23, the purpose of which will be explained later.
  • the apparatus of Figure 1 operates as follows.
  • a normal video signal from the camera 11. is encoded by the encoder 12 so that a normal television receiver receiving the signal from the transmitter 13, satellite 14 or cable 15 will produce a scrambled picture unless the signal is decoded by the decoder 21.
  • the video signal may alternatively be derived in other ways, for example, from a film (ie movie).
  • the decoder 21 will not by itself unscramble the video signal received via the aerial 17 dish aerial 18 or cable receiver 19.
  • the decoder 21 only operates when the card 23 is inserted in the decoder.
  • the card 23 contains electronic components such as a memory and a combination of decoding logic in the decoder 21 and card 23 operate in such a manner as to properly decode the video signal received and to produce an unscrambled signal for the television receiver 22.
  • Such an arrangement allows for the transmission of suitable television type signals in a secure manner.
  • This has many uses including security uses but the primary use is for a pay-television channel.
  • Both the card 23 and decoder 21 include electronic components which operate together to properly decode the signal.
  • the card 23 which is shown in Figures 3 and 4 is of approximate dimensions of a conventional credit card but includes electronic components within the plastic.
  • the electronic components incorporate memory as well as logic elements.
  • the transmitted signal incorporates a further element of information (a "key number") which causes the decoder 21 and card 23 to decode the incoming signal in a particular way.
  • the apparatus thus far described can be used to operate a pay-television system having the following functions.
  • the subscriber to the pay-television service is given a decoder 21 for insertion in the line between his aerial and television receiver.22.
  • This decoder 21 is substantially permanently installed although of course can be removed if the subscriber ceases to pay for the service.
  • the subscriber is provided with a new card 23 and has to return- the used card 23 back to the television system operator.
  • the decoder 21 will only operate with the card 23 inserted.
  • the signal received by the decoder 21 contains not only the video information, some of which is scrambled, but a key number which enables the card and decoder 21 to operate to unscramble the television signal, information regarding the programme being transmitted (each programme may carry an identification number) the information regarding the time and date and if different types of service are to be provided, information regarding the type of service provided. If the subsscriber wishes to watch a particular television programme, the card 23 is inserted in the decoder 21 and the system set in operation. As well as decoding the scrambled video signal, the information regarding the number of the programme being watched, the date and time, is passed from the decoder 21 into an electronic memory in the card 23.
  • the card At the end of a prescribed period, for example a month or three months, or when the card 23 is full, the card is returned to the television system operator and then the information regarding the number of the particular programmes watched and the date and time can be extracted from the memory in the card 23. This enables the subscriber to be billed for the programmes which have been viewed.
  • the decoder 21 may include facilities for allowing an initial one or two minute view of a programme before charging commences. There may thereby be provided a preview button which is pressed and of course the system may be arranged so that the preview button may only be pressed once during the transmission of a particular television programme, a feature which is facilitated by the transmission with the video signal of a number corresponding to that particular programme .
  • all of the cards 23 may be identical in which case when the card 23 is first inserted into the decoder 21, the decoder 21, which includes a particular number identifying the subscriber, causes that number to be impressed on the memory in the card 23.
  • the decoder 21 which includes a particular number identifying the subscriber, causes that number to be impressed on the memory in the card 23. This enables the television operator's computer to identify from whom the card 23 has been returned and also means that the card 23 cannot be inserted into another decoder. Thus fraudulent use of the cards 23 in more than one decoder 21 can be eliminated.
  • the television subscriber pays retrospectively for programmes viewed.
  • An alternative arrangement allows for the card 23 to be prepaid and may include in its memory a certain amount of credit which will allow viewing until the credit within the memory of the card 23 has been used up.
  • the system may also be arranged so that the cards 23 will be valid for a particular period of time, say one month or three months.
  • An advantage of this is that if the cards 23 include a certain amount of logic which is used in unscrambling the video signal, then the unscrambling system can be changed at regular intervals which improves the security of the system.
  • Figure 2 illustrates the encoder 21. It comprises an electronic unit 24, the contents of which will be described in more detail later together with a cathode ray tube 26 which displays the exact video waveform being transmitted, a first monitor 27 which displays the unscrambled picture and a second monitor
  • the decoder 21, card 23 and television receiver 22 of a typical installation are illustrated in Figure 3.
  • the decoder and card are illustrated in greater detail in Figure 4 from which it will be seen that the decoder 21 incorporates a slot 29 into which the card 23 may be inserted, the card incorporating in one edge thereof electrical contacts (not shown) which cooperate with electrical contacts in the slot
  • the decoder further incorporates a channel selection switch 31 which enables the viewer to select one of a variety of pay-television channels, a switch 32 for selecting between 3 types of received signal, that is a free broadcast channel 33 a subscription channel 34 and a "pay-per-vie channel 35". There is also provided a power switch 36.
  • a television picture comprises a series of horizontal lines and the colour and brightness of a particular point along each line is determined by the "chrominance" and “luminance” values respectively at each particular point along each line. So far as signal values are concerned we will generally only be referring to the composite chrominance/luminance signal.
  • the scrambling of the video signal in the present apparatus comprises inverting the signal value of groups of lines through the picture.
  • the first few lines of the picture from the top will not be affected, the next few lines will have inverted signal values, and the next group of lines normal signals values, and the next group of lines inverted signal values.
  • the effect, if used through a television receiver without the benefit of decoding by decoder 21 is a picture with bands of meaningless scrambled information which renders the picture unviewable .
  • the number of lines in each band is different down the height of the picture and as an additional complication the number of lines for each group is freuqently varied.
  • the scrambling pattern in the preferred arrangement ' is changed every six fields (ie 3 pictures).
  • the scrambling pattern is inverted.
  • the lines 1 to 4 are normal, 5 to 7 carry inverted signal 1, 8 to 10 normal, etc, then in field 2 lines 1 to 4 will carry an inverted signal, lines 5 to 7 will be normal, lines 8 to 10 will carry an inverted signal and so on.
  • the scrambling pattern (the number of lines in each successive group of lines) is derived from a key number which is transmitted with the scrambled video signal received from the transmitter.
  • the key number is extracted by the decoder 21 and used as a starter number in an algorithm, part of which algorithm is provided by the decoder 21 and part of which is held in a memory in the card 23 to produce a series of numbers which correspond to the combination of numbers of lines in the groups of lines down the screen.
  • the part of the algorithm in the card 23 is transferred to the decoder 21 and the processing is carried out in the decoder 21.
  • the key number may be 2, and this is fed to the algorithm in the decoder 21 and card 23 to produce a series of numbers for example 4, 3, 2, 1, 4, 2, 3, 4, 1,...
  • the key number can be changed as frequently as desired, for example, every six fields which means that the series of numbers produced by the algorithm will change every six fields.
  • step 10 insert number produced by step 6 into step 1
  • the first group of lines is one line only.
  • step 6 Use figure in step 6 above as a new figure to be inserted in the algorithm so that algorithm proceeds as follows.
  • the key number is changed every few fields and the part of the algorithm in the card can be changed every month or so with the card.
  • Figure 5 shows the signal waveform during the field blanking interval of a normal video signal.
  • the first part of the field blanking interval signal incorporates pre-equalising pulses 41 followed by the field sync pulse 42 followed again by post equalising pulses 43.
  • the relative periods of the pulses are illustrated on the drawing.
  • Figure 6 comprises an enlargment of the part of Figure 5 to the right of the line A when modified in accordance with the preferred aspect of the invention.
  • the first five post equalising pulses 43 remain as before, but thereafter the post equalising pulses 43 are changed as shown.
  • the next signal comprises a timing reference 4,6.
  • This timing reference signal 4,6 is a full line of inverse bla-ck (ie 0.7 volt).
  • the timing reference pulse 46 is followed by five amplitude calibration pulses which comprise four successive voltage levels, the first 48 being at 0.7 volt, the second 49 being at 0.49 volt, the third 50 being at 0.21 volt, and the fourth 51 being at 0 volt.
  • the next pulse 52 comprises a data pulse in which 24 bits of data are transmitted in the form of sub pulses 53 of differing width, a narrow sub pulse 52 indicating a binary "0" and a wider sub pulse 53 indicating a binary "1".
  • the timing reference pulse 46 is provided because, as is well known, each picture on a television screen comprises two interlaced fields, and the signal for the second field is half a line out of phase with the signals of the first field. An accurate timing reference is therefore required which is provided by the pulse 46.
  • Figure 7 shows one of the amplitude calibration pulses 47 in greater detail.
  • the video signal is transmitted in the normal way with the dark areas of the line having a voltage level close to or at the black level, 0 volt and the lighter or whiter areas of the line having voltage levels close to or at 0.7 volt.
  • in principle we aim to turn that part of the line which should be black into white and that part which is white into black and blue into yellow and vice versa. The way in which this is done is to invert the voltage (ie turn a positive voltage value into the corresponding negative value) and then add a fixed value of 0.7 volt.
  • a value of mid grey towards the black level say 0.2 volt becomes 0.5 volt and so becomes closer to white than to black.
  • this particular interval to transmit various signals because the signal which reaches the television receiver is not -that which has been transmitted, the decoder at the television receiver stripping off this signal information. We are thus free to use this part of the video signal for our own purposes.
  • this data pulse includes the key number and is for example 8 bits long in which case there could be 256 possible key numbers.
  • the key number is changed for example every six fields (other multiples of two fields may be used) so that it is not possible to unscramble the picture without the proper apparatus.
  • the data pulse 52 incorporates more than the key number.
  • Other numbers can be used for other purposes.
  • the pulse should include a number which relates to the particular programme being broadcast. As described above this information is necessary for accounting purposes and is stored in the memory of the card 23. Thus if the card is inserted in the decoder 21 and the programme is being watched the programme serial number will be inserted into the memory of the card 23 and when the card 23 is at a later date read by the operator's computer then there is an indication of which programmes were watched.
  • This number may also be used to allow previewing of a particular programme as has already been described.
  • the data pulse 52 may also include information regarding whether the particular programme is a subscription programme or is a pay-per-view programme.
  • the data pulse 52 may also include details of the price of the particular programme so that the user may see how much that particular programme is.
  • the data pulse may include the date and time and other information as required.
  • FIG 8 shows a block diagram of ' the encoder. It is clearly necessary in this system for there to be very accurate timing signals. For example, referring back to Figure 6, the ti ing pulse 46 must be very accurately timed as must the amplitude calibration pulse 47 and the data pulse 53. This requires therefore a rather more accurate timing base than that normally provided in a television syste . Clearly the timing reference must be based on the timing pulses (ie the line sync and field sync pulses) derived from the television camera or other video signal source in use.
  • the video signal from the camera 11 (or other source of video signal) is passed through a filter 61 which removes the chrominance signal from the video signal.
  • the output signal from the filter 61 is then being passed to a sync extractor 62.
  • the signal from the sync ' extractor is a digital signal corresponding to the sync signal received by the sync extractor 62 and is passed to two circuits, the first of which produces a timed output in respect of the line sync and the second of which produces a timed output in respect of the field sync.
  • the output from the sync extractor 62 is applied to a IC 63 which removes those sync pulses which are at twice the line rate and the remaining pulses are passed to phase lock circuit 64.
  • the output of the oscillator 65 is passed to several counters, one of which is illustrated at 66 which thereby produces a count up to 256 for each interval between successive line pulses.
  • the counter 66 therefore divides the period between the beginnings of successive line pulses into 256 equally spaceds intervals and it is thus possible by reading the output of counter 66 to accurately determine any one of the 256 equally spaced points through the line interval from the beginning of the line.
  • the line rate output of the counter 66 is fed to a microprocessor 67.
  • the signal from the sync extractor 62 is passed to a field sync detector 68 which detects the field period and outputs to the microprocessor 67 so that the microprocessors can establish time intervals within the field interval the timing output ' s being given on lines 70 in Figure 8.
  • the microprocessor 67 by looking at the particular values passed to it by the signals from counter 66 and field sync detector 68 is able to determine at any time the number of the line and the field.
  • the particular filter for filtering chrominance in the filter 61 is shown at 71, and the IC for removing twice line rate signals is shown at 72.
  • an edge trigger bistable 81 is triggered 48 microseconds after the start of each line sync signal. Now if the voltage at that particular time is low then there must be a field sync signal present but if the voltate is high then there is not a field sync signal present. Thus the bistable 81 detects whether there is a field sync signal present or not.
  • a bistable 82 of and a counter 83 produce a time window which removes transient signals and spurious field pulses.
  • the microprocessor 67 can therefore define within each field any particular line by counting the field pulse input from the counter 66.
  • FIG. 10 this shows the output end of the encoder in block diagram form.
  • a switch 91 which is timed to operate by timing input on line 92 controlled by the microprocessor 67 and associated hardware.
  • a switch 91 has as inputs the video signal on line 93 and a preset black level voltage signal on line 94.
  • the combined data and white calibration voltage is applied; to the input line 95 of the switch 91.
  • the switch 91 is timed by the input on line 92 so that during the transmission of picture information the video input 93 is connected to the output 100, and during the field blanking interval either the black level voltage signal from line 94 or the white level voltage signal and data from line 95 is passed to the output 100.
  • Switch 104 not only inverts complete lines but also part if the calibration waveform to give inverted white and inverted black.
  • the output signal on line 100 is passed to a differential amplifier 101 which has two outputs 102, 103 which produce complementary signals.
  • line 102 carries one signal
  • line 103 carries an inverted signal.
  • the amplifier 101 also has an input from amplifier 110 which provides the basic 0.7 volt level from a controlled voltage input 111 and from the output, to be described.
  • the two outputs 102, 103 are applied to a switch 104 which is again controlled by a timing output from the microprocessor 67 via line 105.
  • the timing along line 105 controls (a) whether the picture information for a particular line is to be the normal signal from line 102 or the inverted signal from line 103 and (b) whether the black level, or inverse black level, or white level, or inverse white level signals are to be passed to line 106.
  • switches 104 and 91 effectively produce the amplitude calibration pulse 47 shown in Figure 7.
  • the switch 91 is switched so as to connect the black level signal from line 94 to line 100 and the switch 104 is switched to pass the inverted signal from line 103 along to line 106.
  • an inverted black signal value 48 is produced.
  • timing pulses along lines. 92 and 105 switch the switch 91 and switch 104 so that switch 91 passes the white level signal from 99 to line 100 and switch 104 passes the normal signal from line 102 to 106 so that a white level signal 49 is produced.
  • a timing pulse is passed along line 105 to switch the switch 104 and thereby cause switch 104 to pass the inverted white signal from line 103 to line 106 and thereby produce signal level 50.
  • a timing pulse is passed to switch 91 and 104 so as to cause switch 91 to pass the black level signal from line 94 to line 100 and the switch 104 to pass normal level signal from line 102 to line 106 thereby producing the normal black level 51.
  • the output from line 106 is passed to an output amplifier 107 and this then provides the video output which will be modulated for transmission.
  • Figure 11 shows a circuit diagram for the arrangement shown in the block diagram of Figure 10.
  • amplifier 101 sets the voltage level about which it inverts the signal received by looking at the calibrating signal output from amplifier 110.
  • the actual 0.7 volt level is set by the amplifier 110 and is varied by means of the variable potentiometer 114.
  • a feedback clamp 115 is arranged to compare the black level voltage signal produced by component 90 and fed to point 116 with the porch level of the incoming video signal, the comparison being carried out by the differential amplifier 117 which operates to make the two levels the same.
  • the amplifier 117 moves the voltage level of the video input so as to match the black level voltage signal produced at 90.
  • Figure 12 is a block diagram of part of the decoder.
  • the video signal which has been removed from the rf signal is applied to the video input 120 and passed from there to a filter 121 which corresponds generally to filter 61 of Figure 8.
  • Filter 121 filters out the chrominance part of the signal. It is then passed to .a sync extractor 122 which corresponds generally to. sync extractor 62 of Figure 8 where accurate square pulses are produced in synchronism with the line sync pulses received or with the field sync pulses, the pulses produced being accurately timed both with respect to repetition rate and to width.
  • Outputs 123 and 124 from the sync extractor 122 provide vertical sync and field sync signals respectively.
  • a further output from the chrominance filter 121 is passed to the data extractor 125 where the data is stripped from the signal and the data is passed to the data output 126.
  • the video input 120 is also connected to an amplifier 130 which provides a normal video and inverted video output on lines 131, 132 respectively.
  • the signal on line 131 is passed through a buffer 133 and the signal on line 132 is passed through a variable gain buffer 134 and the two signals are then passed to a switch 136 which switches between lines 131 and 132 to provide an output to output amplifier 137 and thence to provide the video output 138.
  • a comparator 139 and a further comparator 141 are also provided.
  • the comparator 139 is provided to compare from lines 131, 132 after the buffers 133, 134, the inverted inverse black with the normal porch value (indicated at 131 in Figure 7) and by providing an output on line 142 to the input of amplifier 130 varies the amplifier 130 so as to make them equal.
  • the comparator 141 again compares the outputs on lines 131 and 132 after the buffers 133, 134 and'it is . arranged to compare the normal white signal level with the inverted inverse white signal level and makes them equal by a control signal along line 143 to the variable gain buffer 134.
  • the comparators 139,141 are controlled to carry out the comparisons at times dictated by signals along lines 144, 146 from the microprocessor 67 which is necessary because the comparators will only be receiving their relevant signals on the lines 131, 132 at particular times during the field blanking interval .
  • the comparator 139 as a result of the comparison will change the DC level of the video signal so as to make the voltage of the porch level and the voltage level inverted black of the inverted signals the same. As mentioned above with respect to Figures 6 and 7, this means that the base voltage level of the video signal can be corrected to compensate for any errors during transmission.
  • the comparator 139 thus produces a corrected video output.
  • the comparator 141 compares the normal white signal with the inverted white on an inverted signal and as a result of that comparison changes the gain of the amplifier 134 so as to correct the linearity.
  • the switch 136 of course is controlled by timing pulses on line 147 from microprocessor 67 to switch the video signal between normal and inverted video in accordance with whether the line is to be inverted or not.
  • the timing signal on line 147 is derived from calculating the algorithm.
  • the data which is extracted at data output 126 contains the key number and is fed to the microprocessor 150 in the encoder which, in combination ith the memory in the card, produces the necessary information regarding which lines are inverted, and this is produced as a timing signal on an output line 152 to switch the switch 149 to select either normal video or inverted video as appropriate.
  • Figure 14 shows another part of the decoder.
  • the output 124 of Figure 12 is used as an input to the part of the circuit shown in Figure 14, Figure 14 including similar parts to that of part of Figure 8, that is the signal is passed to a circuit 165 (corresponding to circuit 63) which removes the signals of twice the line rate frequency, to a phase lock circuit 166 which corresponds to phase lock circuit 64 of Figure 8, and which is used to control the output of a 4 mHz oscillator 167 corresponding to the oscillator 65 of Figure 8.
  • This output is passed to an 8-bit counter 168 corresponding to the counter 66, and outputs therefrom are passed to the microprocessor 67 the circuit diagram for this part of the apparatus is shown in Figure 15.
  • the inputs for the microprocessor are shown at 169.
  • the switches 31 and 32 on the decoder provide inputs to the icroprocessor which accordingly provides suitable entries into the memory in the card.
  • the identification number is stripped from the signal in the decoder and is passed to the microprocessor and thereby to the memory of the card in the relevant manner as determined by the television station.
  • the arrangement is such that, to prevent unauthorised decoding of the scrambled signal, there is insufficient information in the signal during the field blanking interval to determine whether the successive line will comprise a normal signal or an inverted signal and indeed it is not possible to tell from the signal itself whether that signal is inverted or not.
  • each decoder has a particular identification number and the encoder is arranged so as, along with the other information already described, to transmit numbers of decoders which are not permitted to operate. It will conventially be possible to send one or two such numbers during each field blanking interval and so it will take a little time to pass through the complete list of barred identification numbers of the decoders to be switched off.
  • the decoder includes means to extract this information regarding the barred identification numbers and if the barred identification number equates with the identification number of the particular decoder then that decoder will switch itself off and will not be operable thereafter.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Security & Cryptography (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)

Abstract

Système de télévision dans lequel les signaux vidéo sont brouillés, au niveau de l'émetteur, en inversant les signaux de certains groupes de lignes à travers l'image, les signaux transmis comprenant également un nombre clef. Au niveau du récepteur de télévision, un appareil décodeur, en combinaison avec une carte en plastique incorporant des composants de circuits électroniques, utilise le nombre clef pour produire un nombre désiré relatif aux numéros de lignes dont les signaux sont inversés, le décodeur pouvant réinverser les signaux pour produire une forme d'onde vidéo utilisable.
EP19860902755 1985-04-12 1986-04-11 Systeme de transmission video Ceased EP0218703A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8509390 1985-04-12
GB858509390A GB8509390D0 (en) 1985-04-12 1985-04-12 Video transmission system

Publications (1)

Publication Number Publication Date
EP0218703A1 true EP0218703A1 (fr) 1987-04-22

Family

ID=10577528

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19860902755 Ceased EP0218703A1 (fr) 1985-04-12 1986-04-11 Systeme de transmission video

Country Status (3)

Country Link
EP (1) EP0218703A1 (fr)
GB (1) GB8509390D0 (fr)
WO (1) WO1986006240A1 (fr)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3640680A1 (de) * 1986-11-28 1988-06-09 Siemens Ag Bildfernsprecher
US5237610A (en) * 1990-02-01 1993-08-17 Scientific-Atlanta, Inc. Independent external security module for a digitally upgradeable television signal decoder
US5029207A (en) * 1990-02-01 1991-07-02 Scientific-Atlanta, Inc. External security module for a television signal decoder
GB9003325D0 (en) * 1990-02-14 1990-04-11 Enfranchise Sixty Ltd Apparatus and method for controlling access to broadcast signals

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3538243A (en) * 1965-09-23 1970-11-03 Skiatron Elect & Tele Subscription television system
US4081832A (en) * 1976-06-08 1978-03-28 Pay Television Corporation Pay television system, method and apparatus
FR2448826A1 (fr) * 1979-02-06 1980-09-05 Telediffusion Fse Carte d'abonnement pour recepteur de videotex et poste de chargement de ladite carte
US4389671A (en) * 1980-09-29 1983-06-21 Harris Corporation Digitally-controlled analog encrypton

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8606240A1 *

Also Published As

Publication number Publication date
WO1986006240A1 (fr) 1986-10-23
GB8509390D0 (en) 1985-05-15

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