Television – Nonpictorial data packet in television format – Including teletext decoder or display
Reexamination Certificate
2001-12-18
2004-12-14
Hsia, Sherrie (Department: 2614)
Television
Nonpictorial data packet in television format
Including teletext decoder or display
C348S465000, C348S714000
Reexamination Certificate
active
06831703
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the reception of video signals, and more particularly, to the storage of teletext type digital data.
BACKGROUND OF THE INVENTION
Teletext is an ancillary service of television stations designed for the transmission of written information in addition to video information. This written information is displayed on the screen of a television set in the form of teletext pages. Each page is conveyed in the form of a variable number of data packets transmitted in the time intervals corresponding to the frame flyback between two images. A teletext service including a set of numbered pages is thus transmitted non-stop and in cycles. The transmission can be made in the chronological order of pages, but this is not necessary.
A full teletext service of a television station may comprise, for example, 500 pages. Page 100 of the service generally corresponds to a contents page of the service indicating the theme and the reference number (or page number) of certain pages of the service. The total pages of the service is broadcast in cycles, and a broadcasting cycle approximately lasts several tens of seconds. This enables a user to watch the service without necessarily storing all the pages. Broadcasting in cycles also enables the broadcasting station to regularly update its teletext service.
In general, to request the display of a page of the service, the user indicates the page number via a remote control. Through shift commands of the “next page/previous page” type, the user can furthermore move from one page to another in the service. With known navigation systems, such as the TOP or FLOF systems, the user can move about more easily in the service and request the display of a page of his choice without necessarily knowing the corresponding reference number.
For example, with the TOP system, the service is divided into blocks (or subject headings, such as sports) and each block is divided into one or more groups (or sub-headings, such as tennis) comprising a variable number of pages. The system works as follows. When a page of the service is displayed, the TOP navigation system displays a complement at the bottom of the screen. This complement comprises a list of pages close to the page displayed in the form of color links, with each link referring to a nearby page. The user can then very easily access the pages of a group or a block by a remote control. The user no longer needs to search for their reference number by going through the contents page, for example.
Here and throughout the rest of the document, the expressions “close”, “near”, “nearby” and “neighboring” must be understood in the broad sense. A page Y is said to be close to a page X if, when the page X is displayed on the screen, there is a high probability that the user will request the display of the page Y.
For example, pages having consecutive reference numbers or almost consecutive reference numbers are close to one another. For example, pages 198, 199, 201, 202 are close to page 200. Similarly, with the TOP navigation system, the first pages of the block, the group, etc., to which the page X belongs are also pages close to the page Y.
A known circuit
10
for the reception and display of a teletext service comprises, according to
FIG. 1
, a decoder
11
, a filter
12
, a memory
13
, a data memory
14
, a display memory
15
, display means
16
and a screen
17
. The circuit
10
also comprises a data detection circuit coupled to an antenna (not shown) to receive a video signal, extract digital data on a teletext service from this video signal and supply the digital data to the decoder
11
.
The memory
13
comprises a list of requested pages identified by their respective reference numbers. The list of requested pages contains references to pages close to the page being displayed, namely pages for which the probability is high that the user will request the display rapidly. The reference numbers contained in the list may be constant or variable. The contents of the list are updated as a function of the page being displayed and the navigation system used, and the updating is done whenever the display of a new page is requested by the user or whenever an updating of the information on the navigation system is received. The updating can be received after the display of a new page. The updating of the list of pages requested is done by an external list management circuit, which is not shown in FIG.
1
.
The decoder
11
receives the digital data pertaining to a page of the service, decodes them and extracts the corresponding reference number. The filter
12
compares the reference number of the page received with the data on the list of pages requested, and if the received page is a requested page, then the filter
12
sends the memory
14
a storage control signal. The memory
14
stores the received page given by the decoder
11
when it receives the storage control signal. Upon the user's request, a page stored in the data memory
14
is then stored in the display memory
15
. The display means
16
constantly reads the contents of the display memory
15
and copies them on the screen
17
.
When the user requests the display of a page on the screen, the mean time needed for the appearance of this page on the screen depends essentially on the size of the data memory
14
. If a requested page is already stored in the data memory
14
, then the display of this page is immediate. If, on the contrary, the requested page is not stored in the memory
14
, then it is necessary to wait for reception of this page to see it appear on the screen. The wait may be relatively lengthy, given that the same page is broadcast approximately every 40 seconds.
The size of the memory
14
is highly variable, between 1 and 500 kilobytes, for example. For an average quality circuit
10
, a memory of about 10 kilobytes is used, which enables the storage of about ten service pages. This choice results from a compromise between, firstly, the size (in terms of silicon surface area) and the cost of the memory, and secondly, the user's comfort which is directly related to the mean time of display of a page. The choice of the elements of the list of the requested pages reduces the mean display time of a page, given that there is a very high probability that the user will request the display of one of these pages.
One problem appears, however, when the data memory
14
is too small to store all the pages of the list of the requested pages. All the pages of the list are stored in the memory as soon as they are received. Consequently, if a new requested page is received and if the space that is still free in the memory
14
is not enough to store the new received page, then either a previously stored page is totally or partially erased and replaced by the last page received, or else the last page received is not stored.
This is particularly inconvenient for the user because it is possible that the pages closest to the page being displayed will be erased during the storage of a new requested page. When the user requests the display of a nearby page of the displayed page (the most probable assumption), and if this page to be displayed has been totally or partially erased from the memory
14
, or if this page to be displayed has not been stored, then the user must wait for the next transmission of this page to be displayed before seeing it appear on the screen. The user's comfort is thus seriously degraded.
It may be recalled that the expression “closer to” must be understood as follows: a page 1 is closer to a page X then a page Y
2
if, when the page X is displayed, the probability that the user will request the display of the page Y
1
is higher than the probability that the user will requests the display of the page Y
2
. For example, pages 199, 201 are considered to be closer to page 200 than pages 198, 202.
This problem of the erasure of data in the memory arises frequently if the list of the requested pages contains a variable number of references. This problem is also frequent
Albella Arnaud
Tauzia Vincent
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Hsia Sherrie
Jorgenson Lisa K.
STMicroelectronics SA
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