Television – Nonpictorial data packet in television format – Including teletext decoder or display
Reexamination Certificate
2000-10-23
2001-09-18
Eisenzopf, Reinhard J. (Department: 2614)
Television
Nonpictorial data packet in television format
Including teletext decoder or display
C348S461000, C348S465000, C348S473000, C348S478000, C348S705000
Reexamination Certificate
active
06292223
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a receiving device for receiving video and teletext signals.
Such receiving devices are in the mean time commercially available television sets and video recorders in which teletext decoders are integrated. More and more broadcasting corporations are going over to transmitting not only television broadcasts but also additional information for the viewer in the form of teletext pages. In the case of World System Teletext, called teletext for short, the teletext data for the teletext pages to be displayed on the screen can be transmitted in the television lines 6 to 23 and 318 to 353 of the vertical blanking interval of the video signal, assuming a 625 line television system. The teletext data are transmitted continually in a specially encoded format at a bit rate of 6.9375 MHz and 360 bits per teletext line. Each teletext character that is transmitted requires a byte having 7 data bits and one parity bit. In Level 1 of World System Teletext, a teletext page consists of 24 teletext lines which each begin with teletext address data with subsequent teletext data.
The first teletext line of a teletext page has, as teletext address data, a magazine number with subsequent line number, page number, page sub-number and check bits, adjoined by 32 bytes of teletext data. By contrast, the teletext lines 1 to 23 are provided only with the magazine and line numbers as teletext addresses. The page numbers may lie between 100 and 899, the first digit identifying the eight magazines present in the teletext system.
If consecutive information requires more than one teletext page, subpages can be communicated. These subpages are likewise identified in the first teletext line of the teletext page.
The teletext pages transmitted by the broadcasting corporations are transmitted cyclically, that is to say that after all the pages contained in the editorial office of the broadcasting corporation have been transmitted, a cycle is ended. The same pages are retransmitted in the next cycle. In order that the cycle time and, consequently, the waiting time at the receiving end for the user of the teletext service remain reasonable, the number of teletext pages contained in a cycle is limited. The cycle time is about 20 seconds. The number of pages per cycle thus results from the cycle time and the number of teletext data lines used per vertical blanking interval.
In principle, the teletext data are concomitantly transmitted together with the video signal data in the abovementioned time frame, which means that the teletext data are transmitted in specific lines which are indiscernible on the screen. In this case, the teletext data are present at the receiver input in analog form, just like the video signals. In order to be able to decode the teletext data, the latter are regularly separated from the video input signal by a suitable circuit configuration. This is done by a so-called data slicer. In this case, the video input signal, generally the CVBS signal, is clamped by means of a capacitor and sampled by means of a sample & hold circuit, and then digitized in an analog/digital converter. The now digitized teletext signal is fed to a control device or a control block for further processing. A sync information item can be recovered from the digitized data. This sync information is used to establish exactly the time slots for which the teletext data to be decoded are transmitted.
Furthermore, in such receiving devices, a multiplicity of analog signals have to be digitized so that they can be processed further in a microcontroller of the receiving device. One example of such analog signals is the keypad interrogation of a remote control. In that case, by actuating keys, an operator alters for example the volume or the brightness of the picture to be displayed on a screen. This signal is initially present at the remote control receiver in the form of a modulated analog signal, which must be digitized for further processing in the microcontroller.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a receiving device which overcomes the above-mentioned disadvantageous of the prior art devices of this general type in which the design of the receiving device is simplified in comparison with conventional receiving devices and is thus less expensive to produce.
With the foregoing and other objects in view there is provided, in accordance with the invention a receiving device that has a teletext processing device for decoding and providing the decoded teletext signals. The teletext processing device has, on the input side, a clamping circuit with an analog/digital converter device connected downstream, and also a control device for the correctly timed separation of the teletext signals from the video input signal. A switching device is connected upstream of the analog/digital converter device, to which switching device the video input signal which has been passed through the clamping circuit can be fed as a first analog signal to a first input terminal thereof and a second analog signal can be fed at a second input terminal thereof. The switching device can be controlled by the control device in such a way that in time slots in which no teletext signals can be separated from the video input signal, the second analog signal can be fed to the analog/digital converter device.
The principle underlying the invention thus resides in the fact that the analog/digital converter device provided for processing the teletext signals is used for two purposes. In time slots in which no teletext signal, or no signals which are necessary for teletext processing, are separated from the video input signal, the analog/digital converter device is used for other tasks, thus, for example, for interrogation of keypad inputs of an operator control unit.
In accordance with an added feature of the invention, the second analog signal can be tapped off at the output of a further switching device, also called a multiplexer, in which case a plurality of analog signals can be fed to the further switching device on the input side. This further switching device is likewise driven by the control device already mentioned. This development has the advantage that different analog signals can optionally be fed, for digital conversion, to the analog/digital converter device present in the teletext processing device. By way of example, the setting of the brightness, volume, contrast, or the like of a remote control of the receiving device may be provided as the keypad interrogation signal. The second analog signal may also be an AFC signal (Automatic Frequency Control signal).
In accordance with an additional feature of the invention, the video input signal is a television signal, in which case the control device of the teletext processing device connects the switch of the switching device to the first input terminal of the switching device at least for the time slots which are necessary for sync signal separation, and during the reception of the time slots provided for teletext signal transmission. The time slots are currently chosen such that they occur during the reception of the video input signal intended for the video lines 6 to 23 and/or 318 to 353. In these time slots, the switch of the switching device is connected to the first input terminal, with the result that the teletext signals to be processed actually pass to the analog/digital converter device. In the remaining time slots, the switch of the switching device is coupled to the second input, with the result that the analog/digital converter device of the teletext processing device is available for the digital conversion of other analog signals.
In accordance with another feature of the invention, the control device has a detection device which detects whether a teletext signal is present at the input terminal of the teletext processing device. The switch of the switching device is continuously connected to the second input terminal in the absence of a teletext signal. The detection devic
Desir Jean W.
Eisenzopf Reinhard J.
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
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