1191
`United States Patent
`(111=3,924,059
`Horowitz
`[45] *Dee. 2, 1975
`eee
`
`PAY TELEVISION SYSTEMS
`[54]
`Loughlin et alu. 178/5.1
`3/1963
`3,081,376
`
`3,440,338 4/1969)9Walker occ eens 178/5.1
`[75]
`Inventor:
`Irving Horowitz, Eatontown, N.J.
`[73] Assignee: Teleglobe Pay TV System Inc., Rego
`Park, New York, N.Y.
`
`{*] Notice:
`
`The portion of the term of this
`patent subsequent to July 16, 1991,
`has been disclaimed.
`
`Primary Examiner—Maynard R. Wilbur
`Assistant Examiner—S. C. Buczinski
`Attorney, Agent, or Firm—Michael S. Striker
`
`[57]
`
`ABSTRACT
`
`Reference pulses of opposite polarity to the horizontal
`sync pulses are added to the composite television sig-
`nal just preceeding each horizontal sync pulse. The
`video portion of the signal is inverted for randomlyse-
`lected fields. Coding bursts are added to the compos-
`ite signal to indicate whether subsequentfield is in-
`verted. Transmitter clamped to reference pulse level.
`Reference pulse used for AGC in decoder. Video por-
`tion of received signal
`inverted in accordance with
`coding bursts. Audio program signals encoded by
`modulation on suppressed carrier centered above
`References Cited
`audio range. Barker signals transmitted on normal
`audio frequencies.
`UNITED STATES PATENTS
`2,972,009 2/1961)—Roschke wo...cescscseeseeeee 178/5.1
`6 Claims, 16 Drawing Figures
`
`[22]
`
`Filed:
`
`Dec. 28, 1973
`
`{21] Appl. No.: 429,216
`
`Related U.S. Application Data
`{62] Division of Ser. No. 227,582, Feb. 18, 1972, Pat. No.
`3,824,332.
`
`
`[52] U.S. Cho.
`. 178/5.1; 178/DIG. 13
`Int. Cet ceececcssccssersecees HOAN 1/44
`[S51]
`[58]
`Field of Search... 178/5.1, DIG. 13
`
`[56]
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`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 1
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 1
`
`

`

`U.S. Patent
`
`Dec. 2, 1975
`
`Sheet 1 of 12.
`
`3,924,059
`
`FIG.
`
`WAITE
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`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 2
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 2
`
`

`

`U.S. Patent
`
`Dec. 2, 1975
`
`Sheet 2 of 12
`
`3,924,059
`
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`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 3
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 3
`
`

`

`U.S. Patent
`
`Dec. 2, 1975
`
`Sheet 3 of12
`
`3,924,059
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`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 4
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 4
`
`
`
`
`
`
`
`
`

`

`U.S. Patent
`
`Dec. 2,1975
`
`Sheet 4 of 12
`
`3,924,059
`
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`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 5
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 5
`
`

`

`U.S. Patent
`
`Dec. 2,1975
`
`Sheet 5 of 12
`
`3,924,059
`
`
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 6
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 6
`
`

`

`U.S. Patent
`
`Dec. 2,1975
`
`Sheet 60f 12
`
`3,924,059
`
`70 5" OF CODING
`FLIP FLAP (a2
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`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 7
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 7
`
`

`

`U.S. Patent
`
`Dec. 2,1975
`
` Sheet70f 12
`
`3,924,059
`
`FIG.8
`
`ENCOOEP VIDEO OWT
`
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`SIGNAL INPUT
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`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 8
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 8
`
`

`

`oe5%2hOPEC1?B/Gt VINDCFSSINAAIS.
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`U.S. Patent
`
`Dec. 2, 1975
`
`Sheet 8 of 12
`
`3,924,059
`
`20/DA
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`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 9
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 9
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`
`
`
`
`
`
`
`
`

`

`U.S. Patent
`
`Dec. 2, 1975
`
`Sheet 9 of 12
`
`3,924,059
`
`
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`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 10
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`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 10
`
`
`

`

`U.S. Patent
`
`Dec. 2, 1975
`
`Sheet 10 of 12
`
`3,924,059
`
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`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 11
`
`PMC Exhibit 2107
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`

`

`U.S. Patent
`
`Dec. 2, 1975
`
`Sheet 11 of 12
`
`3,924,059
`
`i1
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`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 12
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`PMC Exhibit 2107
`Apple v. PMC
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`
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`
`

`

`U.S. Patent
`
`Dec. 2,1975
`
`Sheet 12 0f 12.
`
`3,924,059
`
`
`
`
`
`QECODETRIGGERFROM907
`
`FROM906
`
`
`
`RESETTRIGGER
`
`FIGS4
`
`PMC Exhibit 2107
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`IPR2016-00753
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`

`

`3,924,059
`
`5
`
`1
`
`PAY TELEVISION SYSTEMS
`
`2
`ail synchronizing and video portions, is transmitted, but
`the reference pulse occupies the levels normally associ-
`ated with the horizontal synchronizing signals. The
`This is a division, of application Ser. No. 227,582
`width of the reference pulse is not sufficiently wide to
`allow synchronizing of a receiver onto said reference
`filed on Feb. 18, 1972, now Pat. No. 3,824,332.
`ulse.
`P The transmitted signal is further encoded by revers-
`BACKGROUND OF THE INVENTION
`ing the polarity of the video signal during randomlyse-
`This invention relates to pay television systems. It is
`lected fields. Encoding bursts are injected into the
`the object of such television systems to encodethe sig-
`nal at the transmitter in such a mannerthat a receiver !9 composite signal prior to transmission to indicate
`cannot furnish a picture unless a decoder is-activated.|whether.or not the subsequentfield has a video portion
`by the subscriber. Activation of the decoder of course
`to be inverted.
`leads to charges for the program received. In known
`The audio portion of the program is encoded by mod-
`methods and arrangements of the above-described
`ulating said program audio signals onto a suppressed
`types, the transmitted signal is encoded by varying the !5 carrier. In a preferred embodiment of the present in-
`timing between the video and synchronizing compo-
`vention, said suppressed carrier is derived from the
`nents, that is selectively retarding or advancing the
`horizontal synchronizing signals and has a frequency
`video componentrelative to the synchronizing signals.
`equal to twice the horizontal line frequency. The fre-
`Key signals are then transmitted which indicate the
`quency range normally occupied by the program audio
`necessary retardation or advance of the signal which 2° signals is used to transmit a barker signal giving infor-
`must be effected in the receiver in order that the final
`mation about the program to the subscriber.
`system furnished to a paying subscriber may have the
`The novel features which are considered as charac-
`video portion of the signal in the correct relationship
`teristic for the invention are set forth in particular in
`relative to the synchronizing portion.
`.
`the appended claims. The invention itself, however,
`In other known systemsof the above-described type, 25 both asto its construction and its method of operation,
`the coding operates on the synchronizing portions of
`together with additional objects and advantages
`the signal. For example, the field synchronizing compo-
`thereof, will be best understood from the following de-
`nents of the television signal may be frequency modu-
`scription of specific embodiments when read in con-
`lated on the picture carrier, while the line synchroniz- 30 nection with the accompanying drawings.
`ing components are coded and then transmitted to sub-
`scriber receivers concurrently with the sound-signal
`BRIEF DESCRIPTION OF THE DRAWINGS
`components on a soundcarrier. Key signals indicating
`FIG. 1 shows the unencoded and encodedtelevision
`the coding schedule of the line synchronizing compo-
`signals of the present invention;
`nents are transmitted to subscriber receivers over a
`FIG. 2 showsthe vertical blanking interval of an en-
`separate channel. Both of the above-described systems 35 codedtelevision signal in accordance with the present
`have definite drawbacks. Thefirst lends itself rather
`invention;
`‘
`readily to unauthorized decoding, the second requires a
`FIG. 3 is a block diagram of the encoderunit;
`great deal of extra equipment since a standard televi-
`FIG. 4 is a more detailed block diagram of the gating
`sion transmitter cannot be used.
`40 generator of FIG. 3;
`FIGS. 5a and 5b show, respectively, the reference
`SUMMARYOF THE INVENTION
`pulse generator and corresponding waveforms;
`It is an object of the present invention to furnish an
`FIG. 6 shows the circuit diagram for the random
`encoding and decoding system and method which al-
`switching pulse generator of FIG. 3;
`lowsuse of a standard transmitter, require relatively lit-
`FIG. 7 is a more detailed block diagram showing the
`tle additional equipmentandstill have a high immunity 45 generation of the reset gate enablesignals;
`to unauthorized decoding.
`FIG. 8 showsthe circuits for the inverting and non-
`It is a further object of the present invention to fur-
`inverting amplifiers of FIG. 3;
`nish a method and system for encoding and decoding
`FIG. 9 showsthe circuit for the reset burst gate of
`the audio signal associated with the program to be
`FIG. 3;
`.
`transmitted, to prevent reception of said audio signal 59
`FIGS. 10@ and 10show, respectively, the spectrum
`without use of the decoding unit.
`usage and the encoding system for the audio portion of
`It is a further object of the present invention to pro-
`the signals;
`vide a Barker audio signal which is audible on a stan-
`FIG. 11 shows a decoder block diagram;
`_dard television signal without decoding, to. give the in-
`FIG. 12 showsthecircuits for the reference pulse and
`formation required by the subscriber to decide whether 55 burst separator of FIG. 11;
`or not to pay for the particular program.
`FIG. 13 showsthe circuit for generating the reset and
`In accordance with the present invention, a standard
`decodetriggers; and
`composite television signal having a video signal with a
`FIG. 14 showsthecircuit for furnishing the enabling
`determined blacklevel signifying picture black and fur-
`signals for the inverting and non-inverting amplifiers of
`ther having synchronizing signals of a determined syn- 9° the decoder.
`/
`chronizing level and polarity relative to said black level
`DESCRIPTION OF THE PREFERRED .
`is encoded by the following steps:
`EMBODIMENTS
`First, a sequence of reference pulses having a polarity
`opposite to said synchronizing polarity, each displaced 65
`A preferred embodimentofthe present invention will
`now be described with reference to the drawing.
`by a determined time interval from a corresponding
`The underlying principle of the present invention is
`one of said synchronizing signals is generated. Said se-
`best understood with reference to FIG. 1 which shows
`quence ofreference pulses is combined with said com-
`posite television signal. The resulting signal, including
`
`the wave formsof both the standard television signal on
`
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`IPR2016-00753
`Page 14
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`

`which the encoder of the present invention operates
`and the signals following the encoding. Reference to
`line A shows a standardtelevision signal having a black
`negative level and negative synchronization pulses. In
`particular, line A shows the interval between two se-
`quential horizontal synchronization pulses. The hori-
`zontal synchronization pulses are labelled respectively
`H, and H,. On the back porch of the horizontal syn-
`chronization pulses are the color bursts which form
`part of the standard color television signal. Following
`the color bursts is the video portion of the signal. This
`is indicated in stylized form, that is a white, grey and
`black level as shown. Of course the actual video signal
`would have variations between these various levels de-
`pending uponthe picture to be transmitted. In accor-
`dance with the present invention, the above-described
`signal is encoded in two ways; first a reference pulse is
`added on the front porch of the horizontal synchroniz-
`ing signals and thesignal is transmitted in such a man-
`ner that the reference pulse occupies the amplitude lev-
`els and has the polarity normally associated with the
`synchronization signal. Although the horizontal and
`vertical synchronization signals are transmitted, these
`are transmitted at opposite polarity to their usual polar-
`ity, thereby preventing a receiver receiving such an en-
`coded signal from synchronizing thereto. Further, the
`width of the reference pulses is made sufficiently nar-
`row that the synchronizing circuits of the receiver do
`not respond thereto. Thus the receiver receiving such
`an encoded signal will see an image which is unsyn-
`chronized both horizontally and vertically, unless the
`decoderis activated by the subscriber.
`As an additional measure, the video portion of the
`signal indicated by the white, grey and black levels in
`the standard signal described above is inverted during
`somefields. The signal is either transmitted in the stan-
`dard black negative or in a black positive fashion
`throughout any oneparticularfield, but the video sense
`may be reversed either from field to field, or else ran-
`domly aswill be described below. Thus notonly is the
`received signal, if not decoded, unsynchronized, but
`also the video levels are inverted. On a normal black
`and white television receiver a substantially blank re-
`sister will result. On a color receiver the luminance por-
`tion of the signal would at least partially cancel out.
`Since on opposite polarity fields, the chrominancesig-
`nal will be 180° out of phase while the sense of the
`color burst remains unchanged,the colors visible will
`have no discernible relation to the true information and
`will flicker strongly according to the random switching
`rate. Further the lack of horizontal synchronization will
`also cause the color burst gate to be unsynchronized
`with the color burst and on most receivers no color
`would bevisible.
`Line B of FIG. 1 shows the encodedsignal including
`the reference pulse. In this case the video portion of the
`signal has not been inverted and the black negative
`level still exists. In the following line, line C, the en-
`coded signal with reference pulse, and sync negative,
`black positive level is shown.
`Line D of FIG. 1 shows the RF envelope and indi-
`cates that the reference pulse represents peak power
`from the transmitter. It should be noted with reference
`to this Figure that the video transmitter sees a standard
`composite television signal except for the absence of
`the front porch of the horizontal synchronization
`pulses. The transmitter clamps at the pulse tip of the
`reference pulse instead of at the pulse tip of the syn-
`
`20
`
`25
`
`30
`
`35
`
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`chronization pulses. A standard transmitter can thus be
`used without modification.
`FIG. 2 shows the vertical blanking interval of the
`standard television signal after encoding.
`It will be
`noted that it
`is a standard vertical blanking interval
`with the vertical synchronizing pulses and equalizing
`pulses intact. The only difference is that the reference
`pulses have been addedonthe front porch of the hori-
`zontal sync pulses. Further it will be noted that decod-
`ing bursts have been added following the equalizing
`pulses. It is the function of these decoding burststo in-
`dicate the polarity of the video signal for the subse-
`quentfield, that is whether the subsequent field will
`have a black positive or a black negative level. Further
`it will be noted that just prior to the first equalizing
`pulses reset bursts are added. As will be described in
`moredetail below, it is the function of the reset burst to
`reset the gate which determinesthe polarity of the sub-
`sequent frame. The use of these reset bursts allows a
`minimum equipment to be used in the decoders. Of
`course this is particularly desirable since there is a far
`larger numberof decoders required than thesignal en-
`coder at the transmitter. In the simplet possible em-
`bodimentof the present invention it is of course possi-
`ble to use a single decoding burst to indicate that the
`subsequent frame will be black positive, for example,
`and to use the absence of decoding bursts to indicate a
`black negative frame. This type of system, although:
`simplest, offers the least security. In order to achieve
`greater security the decoding bursts may contain bursts
`of a numberof frequencies and as manyaseight bursts
`may be used. Thusa greatflexibility in encoding to sig-
`nify the polarity of the next frameis available.
`The block diagram of the video encoderis shown in
`FIG. 3. A standard composite television signal (black
`negative) is furnished at input terminal 10. All parts of
`the signal received at
`terminal 10 are transmitted
`through the non-inverting amplifier 11 except that the
`video portion of those fields for which the video por-
`tion is to be inverted is transmitted through inverting
`amplifier 12. Since the incoming standard composite
`television signal is simultaneously applied to the input
`of both amplifier 11 and amplifier 12, it is obvious that.
`gating signals will have to be provided to switch one
`amplifier on and one amplifieroff at all times. The only
`exceptionis that with particular techniques used in the -
`presentinvention both amplifiers are cut off (furnish-
`ing B* voltage) for forming of the referencepulse. This
`furnishes an extremely reliable reference.
`The required enabling signals are furnished by gating
`generator 15, specifically, the signal on line A enables
`amplifier 11, while the signal on line B enables ampli-
`fier 12. The gating generatorin turn is controlled by the
`horizontal and vertical synchronization signals derived
`from the incoming composite television signal by
`meansof a standard sync separator 13. The output of
`the sync separatoris also used to sample the output of
`a random switching pulse generator whose so-sampled
`output is used to determine whether or not the video
`portion of the subsequentfield is to be inverted, thatis
`whetheror not the signal on line B is to appear during
`the subsequentfield. The sync separator 13 isa stan-
`dard circuit which may for example be found in FIG. 4
`in “Television Service Manual” 3rd Edition, second
`printing, 1970, published by Theodore Audel & Co.
`The circuits associated with units 14 and 15 will be dis-
`cussed in detail below. For the presentit is sufficient
`that an encoded video signal is derived at the combined
`
`
`
`PMC Exhibit 2107
`Apple v. PMC
`IPR2016-00753
`Page 15
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`3,924,059
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`5
`outputs of amplifiers 11 and 12. It is further of course
`necessary that the reset bursts be added to the encoded
`signal. This is accomplished by enabling reset burst
`gate 16 via an output D of gating generator 15 at the
`time of the two horizontal line intervals immediately
`preceding the equalizing pulses in the vertical blanking
`interval (see also FIG. 2). It is further essential that the
`decoding burst indicated as following the equalizing
`pulses during the vertical blanking interval (again see
`FIG. 2) be added to the encoded video signal. This is
`accomplished by enabling either black negative burst
`gate 17 or black positive burst gate 18 via lines E and
`C, respectively. Of course, as mentioned above, in the
`simplest case one of gates 17 and 18 may be eliminated
`entirely and a single gate may be enabled to indicate a
`selected video polarity. In the Figure a plurality of burst
`frequency generators, namely generators 19a through
`i9d are shown. Further shownis a burst frequency se-
`lector 26 which may comprise manually set switches
`interconnecting the burst frequency generators with
`one of the gates 16, 17 or 18. The selected bursts are
`then applied to the encoded video signal whenever a
`particular gate is enabled as discussed above. It should
`further be noted that gates 16, 17 and 18 must befol-
`lowed by a stage having a high output impedanceprior
`to connection to the video throughline 21 carrying the
`encoded video signals, to prevent excessive loading of
`this line. Burst frequency generators 19a through 19d
`are standard oscillators furnishing frequencies of be-
`tween 0.2 and 2 MHZ. A suitable circuit for one of the
`burst gates 16 through 18 and including a suitable cir-
`cuit to effect the high output impedance mentioned
`above is shown in FIG. 9 andwill be discussed in detail
`following the description of said Figure.
`A more detailed diagram of the gating generator 15
`of FIG. 3 is shownin FIG. 4. It should be noted with ref-
`erence this Figure and all other block diagramsofthis
`application, that a 1 output and a 0 outputofa flip-flop
`refer to the states wherein the so-labelled outputs are
`enabled.
`FIG. 4 shows a counter, 100, to whose count and
`reset inputs are, respectively, applied the horizontal
`and vertical synchronizing pulses derived from sync
`separators 13 of FIG. 3. This counteris an 8-bit counter
`and from it may be derived signals signifying particular
`lines in a given field. The random switching pulse gen-
`erator 14 of FIG. 3 is shown embodied in a random
`noise generator 140 whose output comprises both posi-
`tive and negative signals appearing randomly with re-
`spect to time. The output of random noise generator
`14is sampled by a sampling gate 141. When a counter
`output furnishes a signal correspondingto the line be-
`fore the coding bursts, a switch 141 is closed to sample
`the state of the random noise generator.If the output of
`random noise generator 140 is a positive output, this
`will cause a setting of coding flip-flop 142 i.c., the 1
`output is enabled. 1 Outputof codingflip-flop 142 sig-
`nifies that the video portion of the subsequentfieldis to
`be inverted. Thusit is necessary to enable inverting am-
`plifier 12 during the video portion of the subsequent
`field; although non-inverting amplifier 11 mustbe acti-
`vated during the horizontal blanking interval as well as
`the vertical blanking interval even during fields having
`an inverted video signal. Furtherit is necessary to insert
`the appropriate coding bursts, that is to enable black
`positive burst gate 18 at the correct times during the
`vertical blanking interval (see FIG. 2). Thus signal C
`(the enable signal for gate 18) must be furnished during
`
`6
`the particular lines immediately preceding the black
`positive field, and at such times as do not include the
`reference pulse and horizontal blanking pulse. The tim-
`ing for activating line C of FIG. 3 is indicated as coming
`from terminal Z of counter 100. This is a schematic in-
`dication signifying a timing corresponding to the lines
`for.which the coding bursts are required. In theory and
`in the simplest case it could of course be only a single
`line during the vertical blanking interval. Of course, if
`the output of the coding flip-flop 142 had been.a 0 the
`inverting burst pulse gate enable signal E would have
`been generated instead of the signal C. Signal E would
`be generated through AND gate 144, AND gate 144
`furnishes signal. E in response to a 0 outputofflip-flop
`142 occurring simultaneously with signal Z.
`A 1 outputof flip-flop 142 occurring simultaneously
`with a signal from terminal W of counter 100 causes an
`output to appear at the output of AND gate 145which
`in turn sets a polarity of flip-flop 146. Thesignal on line
`W is a signalsignifying the line before the video portion
`of the subsequentfield. It will be noted that both the
`coding flip-flop 142 and polarity flip-flop 146 are reset
`by a signal appearingat terminal Y of counter 100. This
`terminal schematically indicates the time for the reset
`pulse gate enablé signal D of FIG. 3.It will be seen that
`this occurs during the two lines immediately preceding
`the equalizing pulses in the vertical blanking interval.
`Again the reset pulses are timed to avoid interference
`with either the reference pulse, the horizontal synchro-
`nizing pulse or the color burst. Since the resetting of
`the flip-flop is accomplished bythe first of these pulses,
`the second of course will be ineffective and is used for
`reliability only. It will be noted that polarity flip-flop
`146 has a | output only when the codingflip-flop indi-
`cated that thevideo polarity of the next field is to be in-
`verted and for a time period extending from the time
`that the flip-flop is set, namely from the timing of out-
`put W of counter 100, to the timing of output Y of
`counter 160. In other words, the whole vertical blank-
`ing interval is excluded as having a possible 1 output of
`flip-flop 146. Actually, reference to FIG. 2 will show
`that the output of flip-flop 146 ceases just prior to the
`beginning of the blanking interval, that is the last two
`lines of the precedingfield are also excluded. Thussig-
`nal B which appears at the output of AND gate 147,
`one of whose inputsis the 1 output offlip-flop 146, can
`exist only in portions of the signal not including the ver-
`tical blanking interval. It is of course further also re-
`quired to eliminate signal B during the times of the ref-
`erence pulse and.of the horizontal blanking interval.
`This is accomplished by taking the output of reference
`pulse generator 148, inverting it in inverter 149, and
`combining it in an OR gate 150 with the otuputof hori-
`zontal blanking generator 151, after inversion of said
`output by inverter 152. The output signal of OR gate
`15constitutes the second input of AND gate 147. It is
`thus seen that signal B will appearonly for a 1 output of
`coding flip-flop 142 and only for that portion of the
`composite video signal which carries the actual video
`information. The synchronizing intervals will always
`pass through noninverting amplifier 11, since amplifier
`12 will never be activated at times corresponding to
`said signals.
`At any time that signal B is not available, signal A
`must of course be available except during the reference
`pulse, which, in accordance with a preferred embodi-
`ment of the present invention, is inserted into the tele-
`vision signal by cutoff of the amplifiers (11 or 12) pass-
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`3,924,059
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`ing the signal. It is thus seen that signal A is present
`when polarity flip-flop 146 has a 0 output and also dur-
`ing the horizontal blanking intervals. Again, it should
`be remembered that the “zero” outputofflip-flop 146
`is present throughout the vertical blanking interval.
`The horizontal blanking generator 151 of FIG. 4 may
`be a simple monostable multivibrator which is switched
`to the nonstable state by the leading edge of the hori-
`zontal sync pulse and returnsto the stable state after a
`predeterminedinterval whichis set to coincide with the
`horizontal sync pulse interval including the back porch
`in order to permit transmittal of the color burst.
`FIG. 5a shows the reference pulse generator. As
`shown in said Figure, horizontal synchronizing pulses
`are applied to the baseof a transistor 201 whose collec-
`tor is connected to the positive supply line through a
`variable resistance 203 and to ground via a capacitor
`202. The collecto1 is further connected to the positive
`supplyline via a resistance 207 and to the base of a
`transistor 205 via a capacitor 206. The collector of
`transistor 205 is connected to the positive supply line
`through a resistance 208, while the emitters of transis-
`tors 204 and 205 are connected to ground potential
`through aresistance 209.
`Asshownin FIG. 56 capacitor 202 charges in a sub-
`stantially linear fashion through resistance 203 (which
`thereby determines the charging rate) while transistor
`201 is non-conductive. The horizontal synchronizing
`pulses applied at the base of transistor 201 switch the
`transistor to a conductive state shortcircuiting capaci-
`tor 202, and thereby dischargirfgit. It will be noted that
`when the voltage across capacitor 202 reaches the
`pointindicated by P in FIG. 5d, transistor 204 becomes
`conductive, causing transistor 205 to become non-con-
`ductive, and the voltage at its collector to assume sub-
`stantially the voltage of the positive line. This results in
`the generation of the reference pulse which persists
`until receipt of the next subsequenthorizontal synchro-
`nizing pulse at the base of transistor 201. It is thus seen
`that the leading edge of the reference pulse occursat a
`predetermined time preceding the next sequential hori-
`zontal synchronizing pulse, which its trailing edge coin-
`cides with the leading edge of said horizontal synchro-
`nizing pulse.
`FIG. 6 shows the random noise generator and its ac-
`companying sampling gate. In particular a Zener diode
`300 is used as a noise generator and hasits cathode
`connectedto the positive supply line through a resistor
`301. The cathode of Zener diode 300 is further con-
`nected to the base of a transistor 302. Transistor 302
`and subsequenttransistors 303, 304 and 305 serve as
`amplifiers. Further, some band passlimiting may be ac-
`complished by capacitors 306 and 307, respectively
`connected from the collectors of transistors 302 and
`303 to ground. The output of transistor 305 is con-
`nected to the base.of a transistor 308 which, in con-
`junction with transistor 309 constitute an AND gate.
`Normally transistor 309 is saturated, shortcircuiting the
`output of transistor 308. A sampling pulse applied at
`the base of transistor 309 blocks said transistor causing
`an output to appear at the commoncollector connec-
`tion oftransistors 308 and 309 in the event thatthesig-
`nal at the base of transistor 308 is negative. This output
`is furnished to the S input of coding flip-flop 142.
`With reference to FIG. 4, the only thing thatstill
`needbriefly be discussed is how the outputs WXYZ of
`the counter 100 are derived in order that not only do
`they signify the correct count,i.e., permit selection of a
`
`8
`particularline in a field, but that the timing is correct to
`prevent interference with the reference pulse, the hori-
`zontal synchronizing pulse, and the color burst. The
`counter, as is well known, is a binary counter using a
`plurality of flip-flops. Any particular count can be de-
`termined by the correct combination of the outputs of
`various ones of these flip-flops. Reference to FIG. 7
`showsthat selected ones ofthe flip-flops have an out-
`put which is combined in an AND circuit 400. The out-
`p