WO1991012692A1

WO1991012692A1 - Coder-decoder system for television transmissions and electronic card to be employed in decoding mode

Info

Publication number: WO1991012692A1
Application number: PCT/IT1991/000007
Authority: WO
Inventors: Silverio Tripicchio
Original assignee: Tv Code S.R.L.
Priority date: 1990-02-07
Filing date: 1991-02-05
Publication date: 1991-08-22
Also published as: AU7215091A; PL293186A1; IT9047602A1; IT1239581B; IT9047602A0

Abstract

The subject of the present invention is a coder-decoder system for television transmissions comprising, at the transmitting site, a coder circuit (11, 11a, 12, 13, 14) with a coding which can be changed through the variation of a number of operating parameters and, at the receiving site, a decoder circuit with which an electronic card cooperates endowed with variable physical and/or electric and/or magnetic characteristics, such that the combination of the decoder circuit and the electronic card is able to decode the received coded signal and to render it intelligible.

Description

CODER-DECODER SYSTEM FOR TELEVISION TRANSMISSIONS AND ELECTRONIC CARD TO BE EMPLOYED IN DECODING MODE

The present invention generally relates to the systems for coding-decoding television transmissions and more particularly relates to 3 system in which the television transmissions of a given telecasting station are transmitted in a coded form which may be changed according to the choice of the managers of the telecasting station and in which the coded transmissions received by the receiving system are to be decoded so that they can be intelligible to the users.

In a more particular aspect, this invention relates to a decoder system that is able to decode such transmissions no matter how they are coded, and comprising a fixed hardware section and a movable or variable component that enables the fixed hardware section to decode said transmissions coded in whichever way.

In a further more particular aspect, the present invention relates to an electronic card realized with changeable characteristics, adapted to cooperate with said decoder fixed hardware section first of all to enable or disenable it and, in the case of the enabling, to make it operate according to parameters such as to carry out the desired decoding.

As is known, with the proliferation of the telecasting stations, the problem or at least the advantage that the transmissions of a given telecasting station are received only by those users that have paid a fee or otherwise defined equivalent is being encountered.

The problems that one encounters when ascertaining and quantifying the copyright that the telecasting stations have to pay for telecasting certain cinematographic, lyric, narrative, etc. works are also known. Systems for detecting listening indexes of some telecasting stations have been realized in prior art. It is apparent that these verifications are of a purely statistical value and, though their extrapolation can afford sufficiently reliable data, certainly they cannot be of a restricting value unless private agreements occur in this connection. Moreover, certainly they do not establish any tie between the transmitting station and the user.

Coding-decoding systems have also been realized in the prior art in which a given transmitting station radiates inintelligible coded transmissions and affords a decoder device which is to be associated to normal receivers in order to decode and render the trans- missions intelligible to the potential users.

The latter systems have a first drawback consisting in that they establish a rigid link between the telecasting station and the user, similar to that existing with the State bodies, which link is badly accepted by the users. Moreover, they have a second fundamental drawback, consisting in the fact that they do not allow the telecasting stations to mathematically, and thus statistically, control the users themselves, and thereby do not solve, for instance, the problem of exactly quantifying a possible copyright.

The general object of the present invention is to realize a system in which both these drawbacks are avoided and in particular to realize a system that allows an innumerable possibility of coding at the trans- mitting site, and that is able to decode the coming signal no matter how it is coded , with the only aid of a card that integrates the operation of a decoder circuit at the receiving site.

This object is achieved by means of a system that comprises a coder circui t with a coding which can be changed through the variation of a number of operat ing parameters at the transmitting site, and a decoder circuit with which an electronic card cooperates at the receiving site, which card is endowed with physical and/or electric and/or magnetic variable characteristics, such that the combination of the decoder circuit and the electronic card is able to decode the received encoded signal and to render it intelligible.

In this way, a given telecasting station can transmit a program encoded in a given way through a suitable combination of said operating parameters of the decoder circuit. Such a coded program will be receivable, but it will be unintelligible for any receiver and it will be intelligible only by those receivers that are endowed with said decoder circuit and to which an electronic card is operationally associated endowed with characteristics that are in a biunivocal correspondence with said combination of coding parameters so as to allow the decoder to decode the received signal.

Obviously, any other card not having the same characteristics will not be able to enable the decoder in the sense mentioned above.

Again obviously, the presence of the decoder does not prevent the receiver from receiving transrais- sions that haven't been, coded.

As mentioned above, the characteristics of the card can be of physical nature, for instance a higher or a lower reflexion ability or transparence to actinic light or to infrared radiation; of electric nature, for instance zones or bands of particular resistance values or of particular capacitance values, or also the insertion of a printed electric circuit; of electromagnetic nature, as for instance magnetized zones or bands. For the purposes of the present invention all these solutions are equivalent, though some certain solutions can show themselves preferable with respect to the other for economical and commercial reasons.

Further details and advantages of the present invention will be evident from the continuation of the disclosure with reference to the enclosed drawings in which the preferred embodiment is disclosed only as a matter of illustration and not of restriction.

In the drawings:

Figure 1 shows a simplified block diagram of the audio section of the coder circuit employed at the transmitting site;

Figure 2 shows a simplified block diagram of the video section of the coder circuit employed at the transmitting site;

Figure 3 shows a simplified block diagram of the decoder circuit employed at the receiving site;

Figure 4 shows a simplified block diagram of the decoder device referenced as an assembly with the block 311 of Figure 3.

A preferred embodiment will now be discussed with reference to the drawings, with the preliminary remark that the functions indicated in the various blocks are all known per se and are implementable by those skilled in the art by resorting for instance to the various kinds of commercially available integrated circuits. Thus, a detailed description of such circuits is not assumed to be necessary. Moreover, the values and the details that will be given will have a purely indicative value, should a technician require them to realize in practice the invention.

CODER

The coder of Figures 1 and 2 is able to gather the signals coming from the audio and video mixer and to code them through the use of variable, but nonrandom, operating parameters, entered through the utilization offor instance twelve micro switches (not represented) that vary their sequence of logic states, allowing at each time the variation of the coding and consequently of the key for having access to the system to be carried out.

In this way, totally scrambled, and thus not interpretable by a normal television receiver, signals are sent to the audio-video modulator of a transmitter.

As will be seen, a decoder apparatus is employed upstream of the television receiver to render the signals clear and thus visible and audible.

A card or similar device will be utilized having such characteristics that when it cooperates with the decoder, the latter is able to carry out a decoding corresponding to the parameters utilized in the decoder.

With reference to Figure 1, the low-frequency signal is applied to an operational amplifier 11 capable of amplifying ten times the received signal. Successively, the signal amplified at 11 reaches a two-output divider 11A, the extremities of which are applied to the two input ports of an electronic switch 12 whose energization is driven by a square wave oscillator 13 that can vary according to the pre-established encoding from 8,000 Hz to 30,000 Hz.

The sum of two frequencies is so obtained, the low frequency of the audio signal and the frequency of the oscillator 13. Such a sum signal is applied to a low frequency audio amplifier 14 whose output is applied to the transmitter audio modulator.

As regards the video section, with reference to

Figure 2, the input signal coming from the video mixer, then of video frequency, is applied to the circuit 26 capable of separating the synchronism signals from the video signal. The vertical synchronism signals plus the horizontal synchronism signals are sent to an inverter circuit (not shown) capable of intervening in the vertical synchronism peaks only.

The vertical synchronism signals extracted in the block 22 will be utili zed, as mill be done in the decoder also, to reset a 1-to-10 counter, pointed out as 23 in Figure 2. The horizontal synchronism signals, on the contrary, extracted in the block 21 are utilized as a pulsating voltage for the counter 23, applicating them on the gate. In the present invention, this circuit enables during the entire cycle time the closing of an electronic switch (not shown, but considered to be included in block 23) which allows the coding signal locally generated on the basis of the selection of some parameters (as for instance twelve microswitches) to be combined with the signal coming from the mixer for instance only and exclusively in the first ten lines to render the system further inaccessible to third users. The coding signal thus generated in the block 25 (a pulse packet of 1/0 logic state is dealt with in this case) is used to frequency-modulate a carrier wave that can arbitrarily vary from 50 kHz to 4 MHz in the block 24. The so generated signal is sent to the IF transmission modulator.

DECODER

The decoder is able to receive amplitude and frequency modulated VHF and UHF signals for the video and the audio respectively. Moreover, it is able to convert these signals into medium frequency and then into video frequency and low (audio) frequency for the video signal and the audio signal respectively.

Once the transformation has been obtained from the high frequency into the video frequency and audio frequency, information is extracted from the video signal and the audio signal, to supply the decoder with the data necessary for its right operation. As information the various data are meant, that have been previously entered in the video signal and in the audio signal in the stage of transmission by means of the already disclosfid coder.

The audio and video signals, after having been suitably corrected, in the case of the coded transmission, or not , in the case of the clear transmission , are sent to a video+audio modulator and the video signal is amplitude modulated, and the audio signal is frequency modulated, in the decoder, which, as will be seen, is also endowed with a by-pass circuit such that it is able to operate as a normal television (audio and video) demodulator.

With reference now to Figure 3, which shows the decoder section, the RF signal is seen to be applied to a frequency variable amplifier 31 which is able to optimize itself on all the desired television channels, as for instance those of the European standard (I-III-IV and V band) by means of a hand-changeable external voltage. For example, the RF signal is amplified by about 10 dB with a band width of 8 MHz and a gain linearity of ±0,5 on the entire band width.

The output signal of the amplifier 31 is applied to a first port of a mixer 32 which receives a signal generated by a local oscillator 33 at its second port. The mixer 32 mixes the two signals giving a difference conversion.

In an application example, the frequency variation of the local oscillator 33, which can be manually effected by means of the same control of the RF amplifier 31, is previously calibrated so that the difference between the frequency coming from the amplifier 31 and that coming from the local oscillator 33 is always greater than 38,9 MHz at the point of maximum amplification of the RF amplifier 31.

The signal coming from the mixer 32 is filtered by a ceramic band-pass filter of an intermediate frequency, in order to attenuate the channels adjacent to the received signal, the image frequency of the mixer and the signal of the local oscillator.

The signal coming from the medium frequency filter 34 reaches an intermediate frequency filter 35, with a constant gain equal to 30 dB, with a band width of 8 MHz and amplitude tilting of ±0,2 dB. The amplifier is accompanied by an automatic gain control circuit 36 in order to cause the output level of the intermediate frequency amplifier 35 to be constant.

The reference voltage that determines the gain of the amplifier 35 comes as a feedback from the demodulator 37. The automatic gain control circuit 36 is a normal currant amplifier which supplies power enough to drive the intermediate frequency amplifier stages.

The output signal from the amplifier 35 is applied to the input of an AM demodulator circuit which outputs a demodulation negative and positive video signal with a 1 volt (peak-to-peak) magnitude. For instance, such a demodulator can be realized by utilizing a Siemens TDA 5010 integrated circuit.

The output signal from the AM demodulator 37 follows two paths and precisely the video component traverses the blocks 31, 315 and 318 of Figure 3 and the audio component traverses the blocks 39, 312, 316 and 318. The contents of the block 311 is more particularly set forth in Figure 4.

The video signal from the AM demodulator 37 reaches the port of an electronic switch IE whose function is that of retrieving video information from the first ten lines and of sending them to the circuit 47 for enabling the decoder, correspondingly to what is effected in the coder. Upon exceeding the first ten lines, the electronic switch IE opens until it is reached by the subsequent vertical synchronism signal extracted by means of the block 43, which performs the function of resetting the counter 41 which begins counting the line pulses 1 to 10 again, restopping andthen restarting the cycle again. The signal from the electronifc switch IE reaches a FM demodulator 42 which performs the task of discriminating it and of extracting all the frequency variations in such a signal. In this way, two demodulations have been obtained, one from the AM demodulator 37 and the other from the FM demodulator 42. As a consequence, a cross demodulation is obtained of an AM modulated signal which in turn is FM modulated. In practice a pulse packet is obtained corresponding to the pulse packet sent from the transmitting station through the coder circuitry.

This signal is applied to an inverter circuit

44 which in turn returns it to a second inverter circuit 45, to make the signal to return to its positive value. These two circuits 44 and 45 allow the signal to be squared rendering the twelve pulses, referred to in the disclosure, free from spurious harmonics.

This pulse packet is compared in the comparator 47 with another pulse packet produced in the block 46 with the aid of the access electronic card.

If the two pulse packets compared with each other show themselves to have the same characteristics, then the coder is enabled and it carries out the requested decoding to render the signal intelligible.

In case of unsuccessful enabling, which can happen also in the case of a not coded transmission, the automatic insertion is provided with a by-pass block which normally allows the decoder to operate as a standard television (audio-video) demodulator.

The various access configurations, as already mentioned, are manipulated with the aid of a card or similar device that, in a simple embodiment mentioned as a matter of example, has the format of a "visiting-card" made from plastics, thin cardboard or the like, having an index of transparence to ihfrared radiation comprised between 10% and 100%.

By drawing with suitable inks or particularpaints, one can obtain not uniform transparencies or even in some cases the non transparence.

Such a plastics or cardboard card containing the so drawn or otherwise represented figure is inserted in a suitable read housing. The read housing, in the application at hand, provides the use of twelve infrared light beams. The light beams, after having traversed the card, where they succeed in traversing it with an intensity greater than the 50%, are received by as many receivers realized with phototransistors which are able to gather such light beams. The phototransistors are employed as normal electronic switches in which one finds a positive voltage on the collector, the base is polarized by means of the infrared light beam and the emitter allows the collector voltage to be drawn, provided the base is suitably polarized.

All the emitters of the transistors are connected to the control of a MOSFET-like electronic switch which controls the utilized integrated circuit by grounding or not the twelve commands that have been disclosed above.

In other words, if the card doesn't have the transparence at the right points and with the right intensity, the coder will not be enabled and, as it is not enabled, it will cause the insertion of the by-pass branch 310 of Figure 3. That allows the decoder to be utilized as a normal demodulator.

Still with reference to Figure 3, the signal coming from the decoder/enabler 311 or from the by-pass branch 310 is seen to reach the video amplifier 315 which is able to amplify the video signal and to equalize it, if necessary.

The signal output by the video amplifier is applied to the amplitude modulator whose primary characteristic is that of modulating in the UHF band, making one able to apply such a signal to the antenna socket of a normal television receiver. As regards the audio signal, the AM demodulator is seen to supply the 5,5 MHz audio carrier which is sent to the audio demodulator 39. The audio demodulator

39 can be obtained for example by the utilization of a Siemens TBA 120 T integrated circuit.

In particular, the signal coming from the AM demodulator 37 is applied to a 5,5 MHz pass-band-like filter and then to a discriminator built in the same integrated circuit, to finally beat with a 5,5 MHz quartz oscillator of ceramic type, which is also built in the same integrated circuit.

The signal output by the audio demodulator 39 is a low-frequency signal which isn't yet audible in that, upon transmitting it, it has been scrambled through the addition of a subcarrier that inay vary from 9 kHz to 30 kHz according to the predetermined coding. To make the listening of such a low-frequency signal possible, the elimination of the previously added subcarrier is sufficient.

Again with reference to Figure 3, the signal, coming from the demodulator 39 is applied to the block 312, where it is divided into two portions by means of a divider. Such two portions of the demodulated signal are applied respectively to two push-pull MOSFET electronic switches driven by a square wave oscillation corresponding to that employed when transmitting. In this way one obtains the suppression of the subcarrier.

At the output of the two MOSFET switches and then of the block 312 an operational amplifier 316 is provided which operates as a mixer to restore the low- frequency signal, in which the signal, besides being amplified, is suitably filtered to eliminate possible residues of the coding subcarrier.

The audio signal, once made clear, is applied to the already mentioned modulator 318, is combined with the already processed video signal end lastly it reaches the antenna socket of the television receiver.

As already mentioned, it is apparent that, though a preferred embodiment has been described in which the access card comprises zones of differential transparence to infrared radiation and in which its reading is carried out through infrared radiation beams and phototransistors operating as switches, it is apparent that the same function could be performed by cards having resistive zones or bands or concentrated or distributed capacitances, or also suitably magnetized zones or bands, or also proper miniature electronic switches, and the reading can be carried out with suitable sensors or circuits that are able to react to these characteristics to perform the same function of the phototransistors sensitive to infrared radiation.

The use of actinic light also is not to be excluded. The modifications to be made to the card or to the read circuits are entirely within the scope of those skilled in the art in the light of the preceding disclosure and thus a detailed description of them is considered to be pleonastic.

In the above the preferred embodiment has been disclosed and some examples of practical implementation as well as some functional and structural details have been given; however, it is to be expressedly understood that those skilled in the art will be able to make several modifications and variations in the components, in the values, in the parameters and in the circuits, without so departing from the scope of the enclosed claims.

Claims

CLAIMS :

1. Coder-decoder system for television transmissions comprising, at the transmitting sits, a coder circuit with a coding which can be changed through the variation of a certain number of operating parameters and, at the receiving site, a decoder circuit with which an electronic card cooperates endowed with variable physical and/or electric and/or magnetic characteristics, such that the combination of the coder circuit and of the electronic card is capable of decoding the coded received signal and to render it intelligible.

2. Coder-decoder system according to Claim 1, in which said co-operation of the decoder circuit with the electronic card manifests itself by enabling/disenabling the decoder circuit through the comparison between a pulse packet produced on the basis of the coding parameters 3nd contained in the transmitted and received signal and a pulse packet generated in the decoder circuit on the basis of said characteristics of the electronic card.

3. Coder-decoder system according to Claims 1 and 2, in which said coder circuit consists of a video section and of an audio section and in which said video section comprises as fundamental operating parts a synchronism buffer (21), a vertical synchronism (21), a vertical synchronism (22), a 1-to-10 counter (23) driven by said synchronism buffer, a frequency modulator and pulse generator set (24, 25) whose output is sent to the IF modulator, and in which said audio section comprises an audio amplifier (11) whose output is divided into two portions and applied to an electronic switch (12) driven by a square wave pulse generator (13), whose output is applied to an audio amplifier (14) and then sent to the modulator.

4. Coder-decoder system according to Claims 1 and 2, in which said decoder circuit comprises, as fundamental functional portions, a RF amplifier (31) and a local oscillator (33) connected to the two input ports of a mixer (32), followed by an IF filter (34) and by an IF amplifier (35) endowed with an automatic gain control (36), in which, at the output of said IF amplifier (35) an AM demodulator (37) is connected having a video output and an audio output, said video output being connected to an audio-video modulator (318) through a decoder block (311) endowed with a by-pass (310) and said audio output being connected to said audio-video demodulator (318) through an audio demodulator (39), a scrambler circuit (312) and an audio amplifier circuit (316); the output of said audio-video modulator (318) being connected to the antenna socket of the television receiver.

5. Coder-decoder system according to Claim 4, in which said decoder block (311) comprises an electronic switch (IE), driven by a synchronism buffer (43), to which a FM demodulator (42) is connected followed by two inverter circuits (44, 45) to bring the input signal into the start conditions again, the resulting output of said two inverter circuits being applied to a pulse generator (46) and comparator (47) set to compare the received signal with the signal generated in the pulse generator and, on the basis of the result of the comparison, to send an enable/disenable command; said generated pulses being determined by the characteristics of said electronic card.

6. Coder-decoder system according to any one of the preceding claims, in which said card is characterized by zones or bands having different actinic light or infrared light transparence and/or refϋexion values.

7. Coder-decoder system-according to any one of the Claims 1 to 5, in which said card is characterized by zones or bands having different electric resistance values.

8. Coder-decoder system according to any one of the Claims 1 to 5, in which said card is characterized by zones or bands to which various electric capacitance values are connected.

9. Coder-decoder system according to any one of the Claims 1 to 5, in which said card includes a printed or built-in electronic circuit.

10. Coder-decoder circuit according to any one of the Claims 1 to 5, in which said card is characterized by differently magnetized zones or bands.

11. Coder-decoder system according to any one of the preceding Claims, in which said card is inserted in a read and pulse-generating set which generates a pulse packet as a response to the physical or electrical or magnetic characteristics of the card.