Television – Image signal processing circuitry specific to television – Noise or undesired signal reduction
Reexamination Certificate
1998-04-17
2002-08-13
Kostak, Victor R. (Department: 2611)
Television
Image signal processing circuitry specific to television
Noise or undesired signal reduction
C348S723000
Reexamination Certificate
active
06433835
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to apparatus, systems and methods for expanding the ability of existing communication transmission systems to carry information, including but not limited to television broadcast, cable television, microwave systems, closed circuit television, FM broadcast and other closed circuit and broadcast systems.
2. Background
In 1941, the Federal Communications Commission (“FCC”) adopted standards for commercial television broadcasting in the United States. Named after the committee that created it, the National Television Systems Committee (“NTSC”) standard is the approved method for over-the-air transmission of television signals in the U.S. This television technology is an analog system, wherein the picture component is transmitted in a vestigial sideband modulation format on the visual carrier and the sound component is transmitted as frequency modulation on a separate sound carrier. In 1954, the National Television Systems Committee “compatibly” extended the NTSC system to include color information by increasing the utilization of the 6 MHz spectrum occupied by the television channel.
The NTSC standard is termed “analog” because the picture and sound information can take on any value between the minimum and maximum values. An infinite number of values are possible. The picture information is related to the strength of the transmitted signal with black portions of the picture having the most power and white portions of the picture having the least power. Periodic pulses are included at powers greater than those used to represent black areas in the picture. These pulses provide the timing information required to synchronize the transmitter and the receiver so that the picture is shown correctly on the screen. The horizontal synchronization pulses coordinate the left-to-right placement of images on the screen while the vertical synchronization pulses coordinate the top-to-bottom placement of the picture.
The cathode ray tube (“CRT”) was the original display device used in high volume production television receivers. A CRT uses an electron beam to stimulate a phosphor coating on the inside face of a vacuum picture tube. The electron beam scans the tube horizontally and vertically to display a complete image. The strength of the electron beam is inversely proportional to the strength of the television transmitter power and regulates the amount of brightness in the picture. The deflection of the electron beam can be accomplished by electrostatic forces or magnetic forces. Most television display devices used magnetic deflection. Magnetic deflection requires time to move the electron beam back to the left side of the screen after completing a line. During this time, the electron beam must be turned off or blanked to prevent unintended stimulation of the phosphor screen and the resulting interfering light. The period of time during which the electron beam is turned off is called the “horizontal blanking interval.” When the electron beam reaches the bottom of the screen, it must be returned to the top of the screen to continue the process of making pictures. Just as in the horizontal case, the electron beam must be blanked to prevent disturbing light patterns on the screen. This period is called the Vertical Blanking Interval (“VBI”). The VBI is much longer than the horizontal blanking interval. The combination of the two blanking intervals constitutes approximately twenty-five percent of the total scanning time. This time may not be used to convey analog pictures.
The scanned picture area is termed a “raster”. The raster consists of two half-pictures called fields. Two fields make up a complete picture which is called a frame. One field has the even scan lines while the other field has the odd scan lines. The fields are displayed at a rate of sixty fields per second. This technique of using two fields is called “interlace” and reduces the flicker of the image while conserving bandwidth.
The Vertical Blanking Interval
It was determined that other uses can be made of the electron blanking time. For example, the VBI may be used to carry analog test signals that measure the transmission characteristics from the signal source to intermediate points along its path to the final point of use. The VBI may also be used to carry analog signals representing digital data. The data signals may be of two or more levels which are resolved into data bits by appropriate circuits. Since the “digital” signals are of just a few discrete levels, the data detection circuits can discriminate against significant amounts of noise, distortion, and interference. This makes these data signals more robust than the analog Visual signal itself for most forms of interference.
The United States first attempted to use the VBI for ancillary purposes in 1970 when the National Bureau of Standards (“NBS”) proposed to use the VBI for the distribution of precise time information nationwide. The ABC television network was a partner in that effort. While this initiative did not result in a service, ABC recommended a captioning service for the hearing impaired.
The First National Conference on Television for the Hearing Impaired met in Nashville, Tenn. in 1971. The NBS and ABC subsequently demonstrated a captioning service at Gallauded College in early 1972. In 1973, the engineering department of the Public Broadcasting System (“PBS”) initiated development of a captioning service to be funded by the department of Health, Education and Welfare (“HEW”). As a result of this work, the FCC reserved line 21 of field one of the NTSC television signal for the transmission of closed captions in the United States in 1976. In 1979, the National Captioning Institute (“NCI”) was founded to caption programming and to further the cause of captioning. In the early 1980s, Sears Roebuck stores carried a captioning decoder in set top box configuration selling for about $250. In 1989, NCI contracted for ITT Semiconductor Corporation to develop a cost-effective caption decoder microchip for use in television receivers. In 1990, Congress passed the Television Decoder Circuitry Act mandating that new television receivers of thirteen-inch diagonal display measure or greater include caption decoding circuits after Jul. 1, 1993. Approximately twenty million television receivers per year are covered by this requirement. In 1992, NCI, the FCC, and the Electronic Industries Association (“EIA”) developed captioning technical standards. The 1996 Telecommunications Act requires the FCC to promulgate rules requiring closed captioning on Visual programming but allowing exemptions for programming that would suffer an “undue burden”.
The Closed Captioning (“CC”) system is called “closed” because it is turned “on” or “off” depending on the user of the television receiver. Those without hearing impairments and those who understand the spoken words need not be disturbed by text on their screens. The CC system supplies data to appropriate digital and analog circuits that place carefully timed text on the television screen to allow the hearing impaired to read a description of the conversation taking place and have indications of other relevant sounds. Moreover, those who cannot understand the spoken words may have text translated into their native language so that they may follow the program. The CC system uses very low speed data in order to minimize the impact of transmission path problems such as reflections and interfering signals. The data rate for the CC systems is 503,500 bits per second of binary (two level) data. This data rate is expressed as 503.5 Kilobits per second (“kb/s”). This data rate allows only two eight-bit characters to be transmitted per VBI line. If only field one is used, about two lines per second may be displayed. This rate yields 480 bps or 3,600 characters per minute. If the average word is five characters long and is followed by a space, then 600 words can be conveyed per minute. The rest of the VBI line is occupied with both a burst of seven sine wave c
Ciciora Walter S.
Dickinson Robert V. C.
Hartson Ted E.
Encamera Sciences Corporation
Ewing, IV Esq. James L.
Kilpatrick & Stockton LLP
Kostak Victor R.
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