J“:
`
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`
`-4!Q259851_//___~
`
`United States Patent
`
`[191
`
`Haselwood et al.
`
`rm
`
`4,025,351
`
`[451 May 24, 1977
`
`['75]
`
`[S4] AUTOMATIC MONITOR FOR PROGRAMS
`BROADCAST
`Inventors: Donald E. Haselwood, Clea;-wager;
`.
`Carl M. Solar, Largo, both of P13,
`.
`I
`In
`.
`[73] Asslgnee: A.C. Nielsen Company, Norlhbrook,
`In.
`I
`_
`Nov. -28, I975
`
`[22] Filed:
`
`_
`I2” A9131’ N9“ 636’o4l
`32531; 325354
`{s2] U.S. CI.
`H041 9,r'00
`[5l]
`Int. Cl.’ ............... ..
`l53l
`“EM 0159311311 ---------------- -- 35’-5!'3l. 53. 53. 54.
`325-"'6‘t 308? 34372003 178353» DIG 133
`3405147 Rs 147 A» l67'R
`Relerences cued
`UNITED STATES PATENTS
`5:197:
`Thompson et al. ............... .. 1735.:
`3,133,430
`I0}! 9134 Crosby ............... ..
`325l64
`3,845.39]
`3.849.729 1l,’]9'l'4
`Baggem
`.......... .. 32S,r'3l
`..
`3,906,450
`‘N191-'5
`Prado, Jr.
`ITBIDICI. 13
`3,947,624
`3,-'19".-"6 Miyake ..................... ..
`ITBIDIG. 13
`
`
`
`[56]
`
`ABSTRACT
`[57]
`A system for automatically monitoring the programs
`broadcast by network affiliated broadcasting stations
`includes a plurality of remote monitoring sites and a
`tral ofiice for periodically interrogating the remote
`Ce" .
`.
`.
`.
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`fying data, and for storing the data in a change fon-nat
`when the time varying data changes in an unexpected
`manner. An elapsed time clock in each remote moni-
`toring unit generates a record of the elapsed time be-
`tween the unexpected changes.
`Each remote unit includes a minioomputer having a
`read-only memory and a random-access memory. The
`data in the read~only memory serves to establish com-
`mutgilatiogs writ!) the cergltiral ofaice and permits the
`n
`a cess
`ran m-acc
`memo .
`llltefier th: raftilogi-agcess mtfmory gas beellissccessedfilt
`may be reprogrammed to alter the operation of the
`remote monitoring unit to accommodate different data
`formats or different info11'nation_
`
`Primary Examiner—Benedict V. Safourek
`
`36 Claims, 9 Drawing figures
`
`
` 44 LOCAL
`PROGRAM
`SOURCE
`
`
`
`PROGRAM
`SELECTOR_
`
`
`
`
`
`DECODER
`Bi CODE
`STRIPPER
`
`30
`
`36
`
`CENTRAL
`OFFICE
`COMPUTER
`
`
`
`'
`
`"
`
`"H
`
`'
`
`2
`
`_
`
`.
`
`_
`
`Page 1
`
`PMC Exhibit 2081
`
`Apple v. PMC
`|PR2016-00755
`
`PMC Exhibit 2081
`Apple v. PMC
`IPR2016-00755
`Page 1
`
`

`
`U.S. Patent May 24, 1977
`
`H. Sheet 1 of5
`
`4,025,851
`
`NETWORK
`FEED
`
` '0
`
`
`
`
`INTERFACE
`
`24
`
`32
`
`30
`
`VERT
`
`
`MONITOR E DECODER
`COMPUTER
`MINI
`INTERFflCE
`RECEIVER V,DE0
`COMPUTER
`
`
`
`
`36
`
`
`
`38
`
`CENTRAL
`OFFICE
`COMPUTER
`
`
`
`60~
`
`MEMBRY
`
`ROMERAM
`
`36a
`
`36b
`
`TELEPHONE
`L1NE
`
`
`
`4l?Il?.£Z
`
`PMC Exhibit 2081
`
`Apple v. PMC
`|PR2016-00755
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`Page 2
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`PMC Exhibit 2081
`Apple v. PMC
`IPR2016-00755
`Page 2
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`PMC Exhibit 2081
`
`Apple v. PMC
`|PR2016-00755
`
`Page 3
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`ma__
`
`PMC Exhibit 2081
`Apple v. PMC
`IPR2016-00755
`Page 3
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`

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`
`
`U.S. Patent May 24, 1977
`
`I Sheet 3 of5
`
`4,025,851
`
`.Fl6.6'A
`
`PMC Exhibit 2081
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`Apple v. PMC
`|PR2016-00755
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`PMC Exhibit 2081
`Apple v. PMC
`IPR2016-00755
`Page 4
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`
`
`U.S. Patent May 24, 1977
`
`Sheet 4 of 5
`
`4,025,851
`
`
`
`FIG 63
`
`[78
`
`IO MHZ
`CRYSTAL
`
`OSCILLATOR
`
`CLOCK
`
`
`
`
`PMC Exhibit 2081
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`Apple v. PMC
`|PR2016-00755
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`Page 5
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`Apple v. PMC
`IPR2016-00755
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`U.S. Patent May 24, 1977
`
`Sheet 5 of 5
`
`4,025,851
`
`I-‘I6. 60
`
`FIG.
`
`64
`
`66‘
`
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`_ DATA
`
`PMC Exhibit 2081
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`|PR2016-00755
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`

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`
`
`1
`
`AUTOMATIC MONITOR FOR PROGRAMS
`BROADCAST
`
`4,025,851
`
`2
`it is still another object of the present invention to
`provide an automatic monitoring system having re-
`motely located sites that are remotely reprogrammable
`from the central office.
`Still another object is to provide a system for deter-
`mining the viewing habits of home viewers by monitor-
`ing the network identification schedule.
`In accordance with a preferred embodiment of the
`invention, each network originated program is coded
`with a data signal from which each program may be
`identified. This coded data signal may take the form of
`a code identifying the program itself, or the code may
`identify the source of the program and the time that the
`program originated to permit the program to be identi-
`fied from the station logs. The encoding is done by
`placing binary data on line 20 or any other unused line
`in the vertical interval. The coded signal is applied to
`the network where it is received by the network affili-
`ated stations for immediate or delayed broadcast.
`A plurality of monitoring sites are disposed about the
`network coverage area to monitor the programs broad-
`cast by the network affiliates. The monitoring may be
`done remotely by means of a monitor receiver that
`receives the programs broadcast by the network affili-
`ates and recovers the data encoded on line 20. Alterna-
`tively,
`the monitoring unit may be installed on the
`premises of the network affiliate to monitor the pro-
`gram material applied to the transmitter. In the latter
`case, there is no need to transmit the data encoded on
`line 20, and the data may be stripped off by the moni-
`toring unit before the signal is applied to the transmit-
`IE1‘.
`
`BACKGROUND 9}’ THE INVENTION
`A. Field of the Invention
`This invention relates generally to monitoring sys-
`tems, and more particularly to systems for automati-
`cally monitoring the programs broadcast by commer-
`cial television stations.
`
`8. Description of the Prior Art
`Several
`techniques for monitoring t.he programs
`broadcast by commercial television stations are known.
`The simplest technique involves a human monitor who
`watches the programs broadcast at a monitoring site
`and manually logs each program. Automated systems
`have been developed which employ a “picket fence”
`code placed in the upper corners of the picture broad-
`cast by the television station which is automatically
`detected and recorded. Preferably the code is broad-
`cast in such a manner that it is undetectable by the
`viewer. In prior art systems, this is accomplished by
`placing the code in a corner of the television field that
`is not normally visible to the viewer. In other systems,
`the code is placed in a notch that has been filtered out
`of the audio spectrum.
`While these techniques provide a way to monitor the
`television programs broadcast by commercial
`telev_i-
`sion stations, registration problems occur when the bar
`code is recorded on a photographic medium, and when
`the code is placed in the audio spectrum, the code can
`be heard during quiet periods. Furthermore, these sys-
`tems are generally used only to identify commercials,
`and are not particularly suitable for monitoring the
`programs carried by network affiliated television sta-
`tions to detennine whether a network program is being
`carried. This is because of the large amount of data
`involved in monitoring a network program line-up, and
`because no convenient data storage format has been
`developed to store this data. As a result, the effort
`required to monitor all of the network affiliated sta-
`tions and to tabulate the data becomes excessive if
`more than minimal data about the programs broadcast
`is tabulated.
`
`SUMMARY OF THE INVENTION
`
`Accordingly, it is an object of the present invention
`to provide an improved monitoring system that over-
`comes many of the disadvantages of the prior art.
`It is another object of the present invention to pro-
`vide an automated system for monitoring the programs
`broadcast by commercial television stations.
`It is another object of the present invention to pro-
`vide an improved network monitoring system wherein
`each program generated by the network is encoded
`with data representing the program, andfor the source
`of origin and time of origin of the program to permit
`the programs to be subsequently identified at monitor-
`ing sites monitoring the network affiliates.
`It is yet another object of the present invention to
`provide an automated monitoring system having a plu-
`rality of remote sites for monitoring and storing in a
`change type of format the program identifying data
`broadcast by the television stations and for automati-
`cally relaying the stored data together with an indica-
`tion of the time duration of each program to a central
`location upon interrogation by a computer located at
`the central location.
`
`10
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`15
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`20
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`35
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`65
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`In either case, the data recovered from line 20 is
`stored at the remote location in a change format, that
`is, a format wherein the data is stored once, and new
`data is stored only when there is a change in the data.
`In addition, data indicative of the time interval between
`changes in data is stored. The time information permits
`delayed broadcasts to be identified since the real-time
`data will not correspond to the network time data in a
`delayed broadcast.
`Each remote unit is periodically interrogated (usually
`once per day) via telephone line by a centrally located
`computer that controls a mini-computer located in
`each of the remotely located monitor units. Upon inter-
`rogation, the mini-computer causes the stored data to
`be transmitted in blocks to the central computer to-
`gether with error checking data to permit the central
`computer to request the remotely located mini-com-
`puter to retransmit the data in the event that an en-or is
`found. In addition, each remotely located mini-com-
`puter may be reprogrammed by the central computer
`in the event that a modification of the data handling is
`desired. This is accomplished by providing each re-
`motely located mini-computer with a hard-wired read-
`only memory {ROM} that initiates the data processing
`and transmission and a random-access memory (RAM)
`which may be reprogrammed by the central computer
`upon completion of the read-only memory routine.
`DESCRIPTION OF THE DRAWINGS
`
`The invention, and its method of operation, together
`with further objects and advantages thereof, will best
`be understood by reference to the following specifica-
`tion talten in connection with the accompanying draw-
`ings wherein:
`FIG. 1 is a block diagram showing a typical network
`outlet and the network source feeding the outlet;
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`4,025,851
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`4
`that a program was received and the duration of that
`program may be ascertained.
`The decoded data together with the elapsed time
`from the clock 34 are stored in a memory 36, which
`contains a read-only memory 36a and a random-access
`memory 36b, under the control of the mini-computer
`30. A central office computer is connected to each of
`the remotely located monitoring sites by means of a
`telephone line 40 and periodically (usually once a day,
`but more frequently, if necessary) interrogates each of
`the remotely located sites to retrieve the data stored In
`the memory 36. The telephone line 40 may be a leased
`line, or may form part of the telephone company long
`distance network.
`In an alternative embodiment, if access to one of the
`network outlets 18 is available, the monitoring station
`may be placed directly on the premises of the local
`network outlet 18 and may be utilized to monitor the
`video signals applied to the transmitter of the network
`outlet 18. The advantage of locating the remote site
`directly on the premises of the network outlet 18 is that
`the effects of interference, signal fading and reflections
`in the transmission path between the network outlet 18
`and the monitor receiver are eliminated.
`A typical television network outlet 18 (FIG. 3) in-
`cludes a television transmitter 42 which feeds the an-
`tenna 20. Video information is applied to the transmit-
`ter 42 from the network feed line 16 or from a local
`program source 44. A program selector 46 is used
`selectively to connect the network feed line 16 or the
`program source 44 to the transmitter 42 so that either
`a network or a local program may be broadcast. The
`local program source 44 may be one of various pro-
`gram sources including a television camera for broad-
`casting live programs, a flying spot scanner for showing
`movies, or a video tape recorder for playing back video
`taped programs including network programs that had
`been previously taped for delayed broadcast. The out-
`put of the program selector 46 feeds a transmitter feed
`line 50 which applies the selected video program to the
`transmitter 42.
`
`When the monitoring station is located on the prem-
`ises of the network outlet 18, a decoder and code strip-
`per 28', similar to the decoder 28 is interposed between
`the program selector 46 and the transmitter 42. The
`decoder and stripper 28’ serves to retrive the code
`encoded on the line 20 and applies it to the computer
`interface 32 for application to the mini-computer 30.
`Since the code is detected at the network outlet site,
`prior to transmission, there is no need to transmit the
`line 20 code. Therefore, the decoder and code stripper
`28' is provided with apparatus {such as the Tektronix
`Model 1461 Signal Delete-rilnserter previously de-
`scribed) for removing the coded data from the video
`signal before applying the video signal to the transmit-
`ter 42. The computer interface 32, the mini-computer
`30, the clock 34, the memory 36 and the central office
`computer 38 may be identical to similarly designated
`apparatus illustrated in FIG. 2.
`There are a variety of methods for encoding digital
`information onto a video signal. Among these are the
`use of subcarriers placed in nulls of the video signal
`spectrum, or placed in a portion of the audio spectrum
`that has been passed through a notch filter. Other sys-
`tems include the use of alternate black and white verti-
`cal bars in the upper corners of the picture at a location
`where they would not ordinarily be visible on most
`television screens. Other systems encode one of the
`
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`3
`FIG. 2 is a block diagram illustrating one embodi-
`ment of the monitoring system according to the inven-
`tion;
`FIG. 3 is a block diagram of an alternate embodiment
`of the monitoring system according to the invention;
`FIG. 4 is a representation of the program identifying
`data encoded on one of the lines of the vertical interval
`of the video signal;
`FIG. 5 is a more detailed block diagram of the de-
`coder illustrated in FIG. 2; and
`FIGS. 6A, 6B, 6C and 6D comprise a circuit diagram
`of the decoder shown in block diagram form in FIG. 5.
`
`DETAILED DESCRIPTION OF THE INVENTION
`Referring now to the drawings, with particular refer-
`ence to FIG. I, a network program originating from a
`television camera 10 or other source has its line 20 [ the
`twentieth line) of field I (or other suitable line in the
`vertical retrace interval] coded with digital information
`by an encoder 12. The encoder 12 may be any suitable
`custom or commercially available encoder such as the
`Tektronix Model 1461 Signal Deleterflnserter manu-
`factured by Tektronix, Inc. The video information from
`the camera 10 is combined with the coding information
`from the encoder 12 at a mixing point 14 before the
`signal applied to a network feed line 16 which feeds all
`of the local network affiliates such as the network out-
`let 18 shown in FIG. 1. The signal received by the
`network outlet 18 may be applied directly to a trans-
`mitter ( within the network outlet 18) for radiation by
`an antenna 20, or may be recorded (by a video re-
`corder within the network outlet 18} for delayed
`broadcast. A clock 22 is connected to the encoder 12
`to cause a real-time indicative signal to be encoded on
`line 20 of the video signal so that delayed broadcasts
`may be identified.
`In additiion, data identifying the
`source of the program and other information, including
`a reference phase signal, a start of message signal and
`parity bits are encoded on line 20. Also data identifying
`the program itself rather than, or in addition to, the
`program source identifying signal may be inserted. A
`typical format for the information encoded on line 20 is
`shown in FIG. 4.
`The broadcasts of the various network affiliates are
`monitored by monitoring stations located near each of
`the network affiliates. A typical monitoring station
`includes a monitor receiver 24 (FIG. 2) that is tuned to
`the frequency of one of the network affiliates, such as
`the network outlet 18, and receives the signals radiated
`by the network affiliate by means of an antenna 26. The
`monitor receiver 24 may be a specially designed re-
`ceiver or a standard home receiver. The standard home
`receiver may even be a receiver in the home of a viewer
`if it is desired to monitor the viewing habits of typical
`viewers in addition to the programs broadcast. A de-
`coder 28 is electrically coupled to the monitor receiver
`24 and receives the horizontal and vertical synchroniz-
`ing signals as well as the video signal from the monitor
`receiver 24. The decoder 28 processes the video signal
`under the control of the vertical and horizontal syn-
`chronizing signals and recovers the information en-
`coded onto line 2|} and applies the information thus
`recovered to a mini-computer 30 via a suitable com-
`puter interface 32. A clock 34 generates a time base for
`the mini~computer to provide an elapsed time indica-
`tion, and a real-time clock in the central office com-
`puter 38 provides a time reference for the elapsed time
`reading generated by the clock 34. As a result, the time
`
`c-
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`at
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`4,025,851
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`6
`the advantage that it simplifies encoding because the
`source identification code need not be changed each
`time there is a program change, and the program may
`be readily identified by examining the time log of the
`originating station.
`In order to decode the information on line 20, line 20
`must first be identified by the system. This may be done
`by providing logic in the system that can locate line 20
`by detecting the vertical synchronizing pulse from a
`television set and counting horizontal synchronizing
`pulses following the detection of a vertical synchroniz-
`ing pulse to locate line 20. This technique has several
`disadvantages because the vertical synchronizing pulse
`' from a television set may not occur precisely at line I,
`and the processing amplifiers used in most television
`stations to resynchronize the television signals may be
`off by one or more lines due to misadjustrnent, thereby
`changing the time relationship between the vertical
`synchronizing pulse and line 20. In addition, hardware
`must be provided to determine whether the field is an
`odd or an even_ field because the code will be present
`only in field 1.
`As a result, the system according to the present in-
`vention processes several lines following the detection
`of a vertical synchronizing pulse and examines each
`one of the lines for the presence of a code. Sufficient
`storage is provided so that up to six lines may be exam-
`ined for the presence of a code, particularly for the
`presence of a start-of-message code which -will always
`be present regardless of the information contained in
`the code.
`The data recovery hardware (FIG. 5] utilizes a video
`processing amplifier 70 for recovering the data from
`the video signal. The amplifier 70 is connected to any
`suitable video stage of the monitor receiver 24 where
`the level of the video signal is compatible with the input
`level requirements of the amplifier 70. Vertical and
`horizontal synchronizing signal amplifiers 72 and 74
`are connected to the respective vertical and horizontal
`synchronizing circuits (not shown} of the monitor re-
`ceiver 24 for receiving vertical and horizontal synchro-
`nizing signals. The output of the video processing am-
`plifier 70 is connected to a 388-bit data buffer 76 which
`stores the data received from the video processing
`amplifier 70. The capacity of the buiTer"76 is sufficient
`to store data corresponding to slightly more than six
`lines. The outputs of the vertical and horizontal syn-
`chronizing amplifiers 72 and 74 are applied to a syn-
`chronizing logic circuit 78 which controls the loading
`of the video data into the buffer ‘T6 and also applies
`horizontal synchronizing pulses to a second 38 3-bit
`butter 80. The synchronizing logic circuit is controlled
`by a 10 megahertz clock that operates at a frequency of
`ten times the bit rate. The output of the vertical syn-
`chronizing amplifier 72 causes an interrupt request to
`be applied to the mini-computer 30, as does each hori-
`zontal synchronizing signal stored in the buffer 80.
`Accordingly, an interrupt occurs following each verti-
`cal synchronizing signal and after each horizontal syn-
`chronizing signal stored in the buffer 80. Following
`each interrupt, a byte of data corresponding to one line
`of information is read into the mini-computer 30. Dur-
`ing this process, the contents of the data buffer 76 and
`the synchronizing buffer 80 are shifted through the
`respective buffers under the control of the synchroniz-
`ing logic circuit 78. Each time a new horizontal syn-
`chronizing signal is shifted out of the buffer 80, a new
`
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`' scanning lines, preferably the scanning located in the
`vertical interval. The last mentioned technique is the
`technique that has been chosen for use with the moni-
`toring system according to the present invention.
`The system accordingto the present invention en-
`codes line 20 of field 1 with 48 bits of information. Line
`20 of field 1 is within the vertical interval and does not
`appear on the viewing screen, and is therefore not
`visible in a properly adjusted television receiver. The
`choice of line 20, field l is not critical, and other lines
`in the vertical interval could also be coded.
`Typical coding of a line in the vertical interval such
`as line 20 is illustrated in FIG. 4. The scanning line
`begins with a horizontal synchronizing pulse 60 fol-
`lowed by a 3.58 megacycle color burst 62, the latter
`being present when a color program is being broadcast.
`The synchronizing signal 60 and the color burst 62 are
`standard signals used in television broadcasting. The
`beginning of the data occurs approximately 1 1 micro-
`seconds following the beginning of the horizontal syn-
`chronizing pulse. The data includes forty-eight bits of
`information, each bit having a duration of approxi-
`mately one microsecond. The bits are labelled 1
`through 48 in FIG. 4 for purposes of identification. The
`first three bits of the sequence are alternating ones and
`zeros which provide a phase reference to the decoder
`28 (or 28’) to permit the decoder 28 {or 28’) to decode
`the subsequent forty-five bits of the message. The next
`four hits following the phase reference signal comprise
`a start-of-message signal that indicates to the decoder
`23 (or 28’) that a message is about to follow. The par-
`ticular sequence of ones and zeros in the start of mes-
`sage of signal is chosen so that it is not likely to be
`confused with a phase reference signal having errors or
`with noise and video information. The next five bits
`8-12 indicate the source of the program. The live bits
`13—I7 comprise a frame address, i.e., a number ranging
`from 0 to 29 assigned to each of the 30 frames broad-
`cast each second. Bits 18-43 identifying the time that
`the program originated at the network, with bits 18-21
`identifying the month, bits 22-26 the day, bits 27-30
`the hour, bits 31-36 the minute, bits 37-42 the second
`and bit 43 indicating a.m. or p.m. Bits 45-47 are spare
`bits which may be used for any desired purpose, and bit
`48 is a parity bit used for error checking. As an illustra-
`tive example, the waveform shown in FIG. 4 is coded
`with a phase reference 101, a start-of-message code
`0110, a source identification code 11001 (indicating
`Public Broadcasting System, Location 1), a frame ad-
`dress 02, month 06, date 30, 11:55 p.rn.
`The specific format of the data described above is not
`critical, and other suitable data formats may be used.
`The fonnat may be modified as required to accommo-
`date the particular data to be tabulated. The modifica-
`tions to the data format illustrated in FIG. 4 may take
`the form of changes in thenumber of bits allocated to
`each item of information to be transmitted, the order in
`which the various items are transmitted or even the
`type of data to be transmitted. For example,
`in the
`embodiment illustrated in FIG. 4, a broadcast program
`is identified by the source identification code {bits
`8-12} and the time of origin {bits 18-43) serving to
`identify the program. Altematively, a unique program
`identifying code can be generated for identifying each
`program, and used instead of or in addition to the time
`and source identification code; however, the use -of a
`time and source identification code rather than a
`unique program identifying code for each program has
`
`'
`
`-
`
`interrupt request is generated to cause the next byte of
`
`PMC Exhibit 2081
`
`Apple v. PMC
`|PR2016-00755
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`PMC Exhibit 2081
`Apple v. PMC
`IPR2016-00755
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`data to be read out from the buffer 76. The process
`continues until the last horizontal synchronizing pulse
`is shifted out of the buffer 80. During the read out
`process, the mini-computer 30 applies a signal to a line
`84 which causes the synchronizing logic circuit 78 to
`prevent further horizontal synchronizing pulses from
`being applied to the buffer 80 during the read out pro-
`cess.
`
`The video processing amplifier '10 (FIG. 6A) com-
`prises a video amplifier transistor 90 that is coupled to
`one of the video stages of the receiver 24 via a pair of
`oppositely poled electrolytic coupling capacitors 92
`and 94 and by a two-stage low-pass filter comprising a
`pair of resistors 96 and 98 and a. pair of capacitors 100
`and 102. The low-pass filter has a high frequency cutoff
`point that is selected to pass the data encoded on line
`20, and to remove video signal components having
`frequencies above the frequency spectrum of the en-
`coded data. The capacitors 92 and 94 serve to direct
`current isolate the transistor 90 from the monitor re-
`ceiver 24.
`The transistor 90 is connected as an emitter follower
`having a potentiometer 104 as the emitter load and a
`pair of biasing resistors 106 and 108. The potentiome-
`ter IO4 serves as a video gain control for signals applied
`to a comparator 110 which amplifies and limits the
`amplitude of the video signal from the transistor 90.
`The comparator 110 comprises an amplifier operated
`as a comparator having a threshold set at the amplitude
`center of the data. A diode I12 clamps the negative
`peaks of the synchronizing signals to ground, and a pair
`of resistors 114 and 116 determine the slicing or
`threshold level of the comparator 110. A diode I18
`connecting the junction of the resistors 114 and 116 to
`one of the inputs of the comparator I10 serves to com-
`pensate for the temperature variations of the diode
`112. A pair of resistors 120 and 122 bias the inputs of
`the comparator 110. A coupling capacitor 124 couples
`the output signal from the potentiometer 104 to one of
`the inputs of the comparator 110, and capacitors 126,
`128, 130 and 132 serve to bypass the input terminals
`and power supply terminals of the comparator 110.
`The horizontal synchronizing circuit 72 includes an
`amplifier transistor 134 and a monostable multivibrator
`136. The transistor 134 is biased in a normally conduc-
`tive mode by a resistor 138, and periodically rendered
`nonconductive by negative peaks of the horizontal
`synchronizing signal from the receiver 24. Horizontal
`synchronizing signals are applied to the base of the
`transistor [34 via a coupling network including :1 ca-
`pacitor 140 and a resistor 142. The negative peaks of
`the input signal are clamped to ground by a diode 144
`which protects the base to emitterjunction of the tran-
`sistor I34 from reverse polarity voltages.
`The output of the transistor 134 obtained at the junc-
`tion of the collector of the transistor 134 and a collec-
`tor load resistor 146 is applied to the input of the
`monostable multivibrator 136. The monostable multi-
`
`vibrator 136 is responsive to the horizontal synchroniz-
`ing pulses from the transistor I34 and generates a posi-
`tive going fixed duration pulse at its Q output and a
`negative going fixed duration pulse at its 6 output in
`response to each horizontal synchronizing signal. The
`duration of the positive and negative going pulses is
`determined by a capacitor 148, a resistor 150 and a
`potentiometer 152.
`The operation of the vertical synchronizing circuit 74
`is similar to that of the horizontal synchronizing circuit
`
`ll]
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`I5
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`3
`72. The vertical synchronizing circuit includes an am-
`plifier transistor l34’ and a monostable multivibrator
`136'. Other components of the vertical synchronizing
`circuit 74 are similar to corresponding components of
`the horizontal synchronizing circuit 72. Consequently,
`similar components of the horizontal and vertical syn-
`chronizing circuits 72 and 74 are designated by like
`numbers, with the components of the circuit '74 being
`designated by primed numbers. Because of the lower
`frequency of operation of the vertical synchronizing
`circuit 74, the time constant determined by the capaci-
`tor l48', the resistor 150’ and the potentiometer 152'
`is longer than the time constant of the corresponding
`capacitor 148, resistor 150 and potentiometer 152 to
`provide a longer duration output pulse at the output of
`the monostable multivibrator 136’.
`
`In order to decode the data present on line 20, the
`synchronizing logic circuit 78 (FIG. 68) must provide a
`clocking strobe pulse to a line 160 at the center of each
`data bit interval. These clocking strobe pulses must be
`synchronized to the data stream in order for decoding
`to take place. The clocking strobe is generated by the
`IOMI-lz clock 82 which,
`in this embodiment,
`is a
`IOMHZ crystal controlled oscillator. The clock 82
`drives a variable modulo counter 162 which has a nom-
`inal modulo of 10 but which can have its modulo ad-
`
`justed to maintain the synchronizing clock pulses in
`synchronism with the received data bits. A coupling
`capacitor 164 and an inverter 166 are used to couple
`the 10 MHZ signal from the oscillator 82 to the variable
`modulo counter.
`the counter 162 is a
`In a preferred embodiment,
`“Johnson counter” fabricated from a five-stage shift
`register such as a shift register type SN 7496 manufac-
`tured by Texas Instruments, Inc. The Johnsorn counter
`has the advantage that it can be operated at higher
`speed than conventional counters and requires fewer
`stages than a ring counter. For example, the modulus of
`the Johnson counter can be set to 2N or 2N—1. where
`N is the number of stages comprising the shift register.
`This allows a counter having a modulus of 9 or 10 to be
`fabricated from a five-stage shift register. The opera-
`tion of such a counter is described in application bulle-
`tin APP. 851‘ 3 entitled "Micrologic Shift Counters"
`published November 1966 by Fairchild Semiconductor
`Div. of Mountain View, California.
`Operation of the synchronizing logic circuit 78 is
`initiated at each horizontal line by the?) output of the
`multivibrator 136 which sets a bistable multivibrator
`168. The multivibrator 168 applies a signal
`to the
`counter 162 to preset each state of a counter 162 to a
`one after the first zero to one transition from the in-
`verter 166 following the termination of the horizontal
`synchronizing pulse from the multivibrator 136. After
`five counts from the oscillator 82 (5% of a data interval) ,
`the first usable clock strobe occurs on line 160 in ap-
`proximately correct phase with the data. The bistable
`multivibrator 168 is reset on the next input clock pulse
`from the oscillator 82 applied to its input via a pair of
`bistable multivibratots 170 and 172.
`
`A two-stage shift register comprising the pair of bista-
`ble multivibrators 170 and 172 and a pair of NAND
`gates 174 and 176 form a transition circuit which pro-
`vides a transition pulse that is approximately 100 nano-
`seconds wide and occurs zero to 100 nanoseconds after
`
`65
`
`a transition in the video data. The transition signal is
`applied to the counter 162 and to a pair of NAND gates
`178 and 1