United States Patent [191
`Ensinger et al.
`
`[11]
`
`[45]
`
`4,408,225
`Oct. 4, 1983
`
`[54] SUBSCRIPTION TELEVISION DECODER
`[75]
`Inventors: James W. Ensinger, Roselle; Melvin
`C. Hendrickson, Elmhurst, both of
`Ill.
`
`[73] Assignee: Zenith Radio Corporation, Glenview,
`Ill.
`[21] Appl. No.: 280,722
`[22] Filed:
`Jul. 6, 1981
`[51]
`Int. CI.J ............................................... H04N 7/16
`[52] u.s. Cl •..................................... 358/120; 358/122
`[58] Field of Search ................ 358/120, 124, 122, 123
`[56]
`References Cited
`U.S. PATENT DOCUMENTS
`4,081,831 3/1978 Tang et al. .......................... 358/120
`4,095,258 6/1978 Sperber ............................... 358/120
`4,222,068 9/1980 Thompson .
`
`OTHER PUBLICATIONS
`RCA Linear Integrated Circuits Application Note
`ICAN-6802.
`
`Primary Examiner-S. C. Buczinski
`Attorney, Agent, or Firm-Jack Kail
`
`ABSTRACT
`[57]
`A decoder is responsive to a decode authorization sig(cid:173)
`nal for unscrambling a broadcast RF television signal
`having randomly suppressed horizontal blanking and
`synchronization pulses. The decoder comprises a tuner
`having a gated automatic gain control circuit and a
`video detector responsive thereto for developing a base(cid:173)
`band video signal corresponding to the broadcast televi(cid:173)
`sion signal. The decoder further comprises a sync resto(cid:173)
`ration circuit developing a standard horizontal synchro(cid:173)
`nization pulse in response to each suppressed horizontal
`blanking pulse of the baseband video signal, the stan(cid:173)
`dard horizontal synchronization pulses being continu(cid:173)
`ously combined with the baseband video signal for
`operating the automatic gain control circuit and being
`coupled for unscrambling the baseband video signal
`only in response to the decode authorization signal.
`
`5 Claims, 1 Drawing Figure
`
`APPLE EX. 1029
`Page 1
`
`

`
`~
`Vl .
`~ a ('t)
`::s
`
`f""t-
`
`-\0
`
`00 w
`
`14
`
`16
`
`38
`
`40
`
`42
`
`39
`
`VIDEO
`DETECTOR
`
`VIDEO
`SWITCH
`
`EMODULATO
`
`TELEVISION
`RECEIVER
`
`GATED
`AGC
`
`18
`
`36
`
`DATA
`GATE
`
`24
`
`30
`
`AUTH.
`REG.
`
`SYNC.
`RESTORATION
`
`22
`
`32
`
`34
`
`APPLE EX. 1029
`Page 2
`
`

`
`1
`
`4,408,225
`
`SUBSCRIPTION TELEVISION DECODER
`
`BACKGROUND OF THE INVENTION
`The present invention relates generally to improve(cid:173)
`ments in subscription television systems and, more par(cid:173)
`ticularly, to improvements in apparatus for unscram(cid:173)
`bling a broadcast RF television signal having sup(cid:173)
`pressed horizontal blanking and synchronization pulses.
`In subscription television systems television program- 10
`ming signals are transmitted, either "over-the-air" or
`through a suitable cable network, in a scrambled form,
`which signals may be unscrambled for viewing by a
`suitable decoder operating the television receiver of an
`authorized system subscriber. The programming signals 15
`may be grouped into several levels or tiers each repre(cid:173)
`senting a different programming category such as sport(cid:173)
`ing events, movies, etc., with the decoder of a particular
`subscriber being authorized for unscrambling the tele(cid:173)
`vised programming signals in selected categories, the 20
`televised programming signals in the remaining unau(cid:173)
`thorized categories being coupled to the television re(cid:173)
`ceiver in a scrambled and unviewable form. Of course,
`in such a system, all the programming signals will be
`reproduced in a scrambled and unviewable form in a 25
`normal television receiver.
`Horizontal synchronization suppression techniques
`are commonly used to effect a scrambled broadcast
`television signal by suppressing the horizontal blanking
`and synchronization pulses below the average video 30
`level of the television signal. This causes the horizontal
`deflection system of a television receiver to lock on
`random video peaks during the active or video trace
`line portion of the video signal rather than on the actual
`horizontal synchronization pulses. In addition, the abil- 35
`ity of the television receiver to use the color reference
`burst associated with the horizontal synchronization
`signals is severely degraded thereby causing inaccurate
`color reproduction. U.S. Pat. No. 4,222,068, to Thomp(cid:173)
`son, teaches a system employing the foregoing tech- 40
`niques wherein an encoder is provided for modifying a
`broadcast television signal by suppressing the amplitude
`of randomly selected horizontal blanking and synchro(cid:173)
`nization pulses during the fields of the video signal.
`Each system subscriber is provided with a decoder 45
`whose front end comprises conventional tuning, inter(cid:173)
`mediate frequency and video detection stages. Also, a
`gated automatic gain control circuit, adapted for re(cid:173)
`sponding to the tips of standard NTSC horizontal syn(cid:173)
`chronization pulses, is provided for controlling the gain 50
`of the tuning and intermediate frequency stages in ac(cid:173)
`cordance with the output of the video detection stage.
`A sync restoration circuit is operable in response to the
`suppressed front porch of each suppressed horizontal
`blanking pulse developed at the output of the video 55
`detection stage for producing a standard NTSC hori(cid:173)
`zontal synchronization pulse, which standard horizon-
`tal synchronization pulses are continuously coupled to
`an input of the automatic gain control circuit for insur-
`ing proper operation thereof and also continuously 60
`inserted in the video signal developed at the output of
`the video detection stage for achieving an unscrambled
`video signal. The video signal including the restored
`horizontal synchronization pulses is impressed on a
`standard television channel RF carrier by a remodula- 65
`tor and then coupled as an unscrambled RF television
`signal to the antenna inputs of a television receiver.
`Each decoder additionally includes a decode authoriza-
`
`2
`tion circuit storing a unique subscriber code which is
`compared to a subscriber authorization code transmit(cid:173)
`ted during a horizontal line of the vertical interval of
`the broadcast television signal. If the stored subscriber
`code and the transmitted subscriber authorization code
`results in a favorable comparison, a decode authoriza(cid:173)
`tion signal is developed enabling the remodulator for
`coupling the unscrambled signal to the television re(cid:173)
`ceiver for viewing, the remodulator otherwise being
`disabled. The system disclosed in the Thompson patent
`therefore requires the use of a relay or other relatively
`expensive switching circuit for selectively enabling and
`disabling the remodulator. In addition, when the
`remodulator is disabled in response to the absence of a
`decode authorization signal, a noisy video image is
`nevertheless produced on the viewing screen of the
`television receiver which frequently leads to the annoy(cid:173)
`ing situation wherein the viewer mistakenly assumes
`that the decoder is malfunctioning.
`In order to alleviate these and other problems, modi(cid:173)
`fications of the decoder taught in the Thompson patent
`have been proposed wherein the restored horizontal
`synchronization pulses are gated for operating the auto(cid:173)
`matic gain control circuit and for insertion in the video
`signal path for unscrambling the broadcast television
`signal only in response to the development of a decode
`authorization signal. These modified decoders also typi(cid:173)
`cally include a video switch connected in the video
`signal path between the video detection stage and the
`remodulator for selectively controlling the application
`of the video signal to the input of the remodulator.
`Thus, when the video switch is operated for establish(cid:173)
`ing the video signal path a scrambled video signal is
`coupled to the remodulator in the absence of a decode
`authorization signal and an unscrambled video signal is
`coupled to the remodulator by gating the restored hori(cid:173)
`zontal synchronization pulses for operating the auto(cid:173)
`matic gain control circuit and for insertion in the video
`signal path in response to the development of a decode
`authorization signal. In accordance with this decoding
`technique, it will be appreciated that during the absence
`of a decode authorization signal the automatic gain
`control circuit will not function properly due to the
`suppressed level of the horizontal synchronization
`pulses. Moreover, it has been found that upon the devel(cid:173)
`opment of a decode authorization signal, an extended
`delay (sometimes of up to several minutes) is encoun(cid:173)
`tered before the automatic gain control circuit initiates
`proper operation in response to the restored horizontal
`synchronization pulses. As a result, an unacceptable
`picture is produced on. the viewing screen of the televi(cid:173)
`sion receiver for a time interval even though the sub(cid:173)
`scriber has been authorized to decode the broadcast
`signal. This condition is quite annoying to the viewer
`and hence poses an undesirable situation.
`It is therefore, a basic object of the present invention
`to provide an improved decoding apparatus operable
`for unscrambling a broadcast RF television signal char(cid:173)
`acterized by suppressed horizontal blanking and syn(cid:173)
`chronization pulses.
`It is a more specific object to the invention to provide
`a decoder of the foregoing type wherein the remodula(cid:173)
`tor associated therewith is continuously operable inde(cid:173)
`pendent of the development of a decode authorization
`signal and wherein the automatic gain control circuit
`associated with the tuning stage of the decoder is re(cid:173)
`sponsive for immediately assuming a proper operating
`
`APPLE EX. 1029
`Page 3
`
`

`
`3
`mode upon the development of a decode authorization
`signal.
`
`BRIEF DESCRIPTION OF THE ORA WINGS
`The features of this invention which are believed to
`be novel are set forth with particularity in the appended
`claims. The invention, together with its objects and the
`advantages thereof, may best be understood by refer(cid:173)
`ence to the following description taken in conjunction
`with the accompanying drawing in which the sole FIG(cid:173)
`URE illustrates the decoder of the present invention in
`block diagram form.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`Referring now to the drawing, there is illustrated a
`subscription television decoder selectively operable for
`unscrambling a broadcast RF television signal having
`suppressed horizontal blanking and synchronization
`pulses. An RF television signal of this type may be 20
`derived, for example, from a television signal transmit(cid:173)
`ter as disclosed in the previously mentioned Thompson
`patent, the transmitter including an encoder adapted for
`modifying a standard NTSC television signal by sup(cid:173)
`pressing the amplitude of randomly selected horizontal 25
`blanking and synchronization pulses during the fields of
`the video signal. As a result of this signal suppression,
`the horizontal deflection system of a normal television
`receiver will lock on random video peaks during the
`active or video trace line portions of the video signal 30
`rather than on the actual horizontal synchronization
`pulses resulting in the production of a scrambled video
`image on the viewing screen of the television receiver.
`In addition, the ability of the television receiver to use
`the color reference burst associated with the horizontal 35
`synchronization signal is severely degraded causing
`inaccurate color reproduction. The Thompson encoder
`is additionally adapted for transmitting a subscriber
`authorization code in serial format during a selected
`horizontal line of the vertical interval of the broadcast 40
`television signal. As will be explained in further detail
`hereinafter, the present invention contemplates the
`transmission of a program authorization code adapted
`for identifying the level or tier of the programming
`information being transmitted by the accompanying 45
`television signal. A subscriber authorization code as
`taught in Thompson may or may not be transmitted
`together with the foregoing program authorization
`code.
`Returning now to the drawing, the decoder com- 50
`prises an antenna 10 adapted for intercepting the broad(cid:173)
`cast RF television signal, which is usually although not
`necessarily transmitted in the UHF band, for applica(cid:173)
`tion to a conventional television receiver tuning stage
`12. As is well known in the art, tuning stage 12 converts 55
`the received RF television signal to an intermediate
`frequency signal which is coupled through an interme(cid:173)
`diate frequency amplifier 14 to the input of a video
`detector 16. The output of video detector 16 comprises
`a composite baseband video signal reflecting both the 60
`video and synchronization signal components of the
`broadcast television signal. Thus a standard NTSC
`composite baseband video signal is developed at the
`output of video detector 16 except that randomly se(cid:173)
`lected horizontal blanking and synchronization pulses 65
`are characterized by suppressed amplitudes. The de(cid:173)
`coder further comprises a conventional gated automatic
`gain control circuit 18 of the type responsive to the tips
`
`4,408,225
`
`4
`of standard NTSC horizontal synchronization pulses
`for controlling the gains of tuning and intermediate
`frequency stages 12 and 14. Automatic gain control
`circuit 18 may, for example, comprise RCA integrated
`circuit CA3154G. In the decoder of the invention, the
`output of video detector 16 is coupled to one input of a
`summer 20 for operating automatic gain control circuit
`18. However, since the amplitudes of random horizon(cid:173)
`tal synchronization pulses developed at the output of
`10 video detector 16 are suppressed below the average
`video level, the automatic gain control circuit will func(cid:173)
`tion in an extremely eratic manner. While such eratic
`behavior of the automatic gain control circuit can be
`tolerated when the decoder is not being operated in a
`15 decode mode, it is desirable that proper operation ensue
`immediately upon changeover to a decode mode of
`operation. In accordance with the present invention,
`the foregoing is accomplished by coupling the output of
`a sync restoration circuit 22 to a second input of sum(cid:173)
`mer 20. Sync restoration circuit 22 is responsive to the
`output of video detector 16 for sensing the suppressed
`front porch of each suppressed horizontal blanking
`pulse for developing a properly timed standard NTSC
`horizontal synchronization pulse, which restored hori(cid:173)
`zontal synchronization pulses are combined with the
`composite baseband signal developed at the output of
`video detector 16 by summer 20. The output of summer
`20 therefore comprises a fully restored composite base(cid:173)
`band signal adapted for properly operating automatic
`gain control circuit 18. As a consequence, whether or
`not the decoder is being operated in a decode mode,
`standard horizontal synchronization pulses are continu(cid:173)
`ously applied to the input of automatic gain control
`circuit 18 for insuring proper operation thereof.
`The decoder of the invention further comprises a data
`gate 24 connected to the output of video detector 16
`and operable for gating the vertical interval horizontal
`line containing the transmitted program code to the
`input of a multibit shift register 26. The program code
`thereby stored in shift register 26 is applied to one input
`of a comparator 28 for comparison with a subscriber
`authorization code stored within a storage element such
`as register 30. The stored subscriber code comprises an
`authorization code identifying the levels or tiers of
`programming the subscriber is authorized to receive.
`For example, assuming that the system encompasses
`five different programming categories or tiers, the au(cid:173)
`thorization code would consist of five bits, one for each
`programming category, with a logical 1 bit indicating
`that the subscriber is authorized to receive televised
`programming within the respective category and a logi-
`cal 0 bit indicating that the subscriber is not authorized
`to receive the televised programming with the associ(cid:173)
`ated category. The program code stored in shift register
`26 also comprises five bits each identifying a respective
`programming category, the bits identifying the cur-
`rently transmitted programming category being logical
`I and the remaining bits being logical 0. Thus, if com(cid:173)
`parator 28 detects a match between the logical I bit of
`the transmitted program code stored in shift register 26
`and the corresponding bit of the subscriber authoriza-
`tion code stored in register 30, a decode authorization
`signal is developed on a first output conductor 32 of
`comparator 28 and a switching control signal is devel(cid:173)
`oped on a second output conductor 34 of the compara(cid:173)
`tor. If the stored subscriber authorization code indicates
`that he is authorized to receive at least one program(cid:173)
`ming category although not the programming category
`
`APPLE EX. 1029
`Page 4
`
`

`
`4,408,225
`
`5
`identified by the program code stored in shift register
`26, only the switching control signal is developed on
`conductor 34. If the subscriber is not authorized to
`receive any of the programming categories, as reflected
`by the stored authorization code in register 30, then
`neither a decode authorization signal nor a switching
`control signal is developed by comparator 28.
`The decode authorization signal is coupled by con(cid:173)
`ductor 32 to the enable input of a gate 36, the data input
`of gate 36 being supplied from the output of sync resto- 10
`ration circuit 22, while the switching control signal is
`coupled to the enable input of a video switch 38 con(cid:173)
`nected in the video signal path. Thus, if the subscriber is
`authorized to receive the televised programming both
`gate 36 and video switch 38 are enabled. The restored 15
`horizontal synchronization pulses developed by sync
`restoration circuit 22 are coupled through gate 36 to
`one input of a second summer 39 for combination with
`the composite baseband signal which is coupled from
`video detector 16 to the second input of summer 39. As 20
`a consequence, the output of summer 39 comprises an
`unscrambled baseband video signal having fully re(cid:173)
`stored horizontal synchronization pulses. The unscram(cid:173)
`bled video signal is coupled from summer 39 through
`enabled video switch 38 for application to a continu(cid:173)
`ously operating remodulator 40. Remodulator 40 ampli- 25
`tude modulates the unscrambled composite baseband
`video signal on a standard NTSC television channel RF
`carrier, usually channel 3 or 4, for application to the
`antenna terminals of a normal television receiver 42
`which, in turn, produces a corresponding unscrambled 30
`video image on its viewing screen.
`On the other hand, if comparator 28 only develops a
`switching control signal on conductor 34 but not a
`decode authorization signal on conductor 32, then
`video switch 38 remains enabled but gate 36 is disabled. 35
`As a result, the restored horizontal synchronization
`pulses are not inserted in the video signal path and a
`scrambled signal is coupled through video switch 38
`and remodulator 40 for application to television re(cid:173)
`ceiver 42. Finally, if comparator 28 develops neither a 40
`switching control signal nor a decode authorization
`signal both gate 36 and video switch 38 will be disabled.
`As a result, remodulator 40 is operable for coupling a
`blanked or black level video signal for producing a
`blanked image on the viewing screen of television re- 45
`ceiver 42.
`What has thus been shown is an improved decoder
`circuit for unscrambling a broadcast RF television sig(cid:173)
`nal characterized by suppressed horizontal blanking and
`synchronization pulses. The decoder is operable for 50
`continuously coupling restored horizontal synchroniza(cid:173)
`tion pulses to the automatic gain control circuit associ(cid:173)
`ated with the decoder's tuning stage so long as a scram(cid:173)
`bled signal is received and is further operable for insert(cid:173)
`ing the restored horizontal synchronization pulses in the 55
`video signal path for unscrambling the video signal only
`in response to a decode authorization signal.
`While a particular embodiment of the invention has
`been shown and described, it will be obvious to those
`skilled in the art that changes and modifications may be 60
`made without departing from the invention in its
`broader aspects. Therefore, the aim in the appended
`claims is to cover all such changes and modifications as
`fall within the true spirit and scope of the invention.
`What is claimed is:
`1. A decoder for unscrambling a broadcast RF televi(cid:173)
`sion signal used to transmit one or more levels of pro(cid:173)
`gramming information, said television signal being char-
`
`6
`acterized by randomly suppressed horizontal blanking
`and synchronization pulses and including a program
`code identifying the level of programming information
`currently being transmitted, said decoder comprising:
`means for receiving and converting said broadcast
`RF television signal to a corresponding baseband
`video signal, said receiving and converting means
`including a gated automatic gain control circuit
`operable in response to the horizontal synchroniza(cid:173)
`tion pulses of a standard television signal;
`means storing a subscriber authorization code identi(cid:173)
`fying one or more of said levels of programming
`information;
`means for developing a decode authorization signal in
`response to the detection of a predetermined rela(cid:173)
`tionship between said stored subscriber authoriza(cid:173)
`tion code and the program code characterizing said
`transmitted television signal;
`means developing a standard horizontal synchroniza(cid:173)
`tion pulse in response to each suppressed horizontal
`blanking pulse of said baseband video signal; and
`first circuit means for combining said baseband video
`signal with said standard horizontal synchroniza(cid:173)
`tion pulses for continuously operating said gated
`automatic gain control circuit;
`second circuit means operable independently of the
`first circuit means for combining said baseband
`video signal with said standard horizontal synchro(cid:173)
`nization pulses for unscrambling said baseband
`video signal only in response to the development of
`said decode authorization signal.
`.
`2. A decoder according to claim 1 including means
`for remodulating said unscrambled baseband video sig(cid:173)
`nal on a standard television channel RF carrier.
`3. A decoder according to claim 1 wherein said first
`and second circuit means comprise first and second
`summers respectively.
`4. A television signal decoder responsive to a decode
`authorization signal for unscrambling a broadcast RF
`television signal having randomly suppressed horizontal
`blanking and synchronization pulses comprising:
`tuning means for receiving and converting said
`broadcast RF television signal to a corresponding
`intermediate frequency signal, said tuning means
`including a gated automatic gain control circuit
`operable in response to the horizontal synchroniza-
`tion pulses of a standard television signal;
`detection means responsive to said tuning means for
`converting said intermediate frequency signal to a
`corresponding baseband video signal;
`means developing a standard horizontal synchroniza(cid:173)
`tion pulse in response to each suppressed horizontal
`blanking pulse of said baseband video signal;
`first summing means responsive to said baseband
`video signal and to said standard horizontal syn(cid:173)
`chronization pulses for continuously operating said
`gated automatic gain control circuit; and
`second summing means operable independently of
`the first summing means and responsive to said
`baseband video signal and to said standard horizon(cid:173)
`tal synchronization pulses for unscrambling said
`baseband video signal only in response to said de(cid:173)
`code authorization signal.
`5. A television signal decoder according to claim 4
`65 including means for remodulating said unscrambled
`baseband video signal on a standard television channel
`RF carrier.
`
`*
`
`*
`
`APPLE EX. 1029
`Page 5