JPH0537547Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an automatic station searching device for setting only channels in use in a television receiver having an electronic channel selection circuit using a synthesizer method. It is.

[Conventional technology]

Synthesizer methods used in electronic tuning circuits include a voltage synthesizer method that stores the tuning voltage of each channel, and a voltage synthesizer method that stores the tuning voltage of each channel, and the tuning frequency of each channel (in addition to the frequency value itself, the frequency division ratio for the oscillation frequency of the reference oscillator, etc.) ) is used as a frequency synthesizer method. In addition, the storage device for storing the tuning voltage and tuning frequency is provided with a plurality of storage areas, and the tuning voltage and tuning frequency can be stored directly by the channel selection button or sequentially by the up/down button.
Channels set in each storage area can be selected. In each of these storage areas, for example in Japan, 1 to 12 channels of VHF are normally set when the television receiver is shipped. However, if channels that are not used in the area are set in this storage area, it is inconvenient when selecting a station, and it is not possible to receive UHF channels when shipped. Therefore, each storage area can be configured to have an arbitrary channel set by the user's operation. However, the operation of setting a desired channel in each storage area of a storage device is very troublesome and imposes a heavy burden on the user.

Therefore, in such a television receiver,
Conventionally, automatic station search devices have been equipped that can automatically set only the channels actually used in the area by the user's operation. This automatic station searching device starts operation in order from channel 1, for example, and detects video signals in several MHz before and after the frequency of the channel in each channel, and only when a video signal is detected, the channel is switched on. This device is configured to sequentially set data in each storage area in the order of detection. Therefore, when this automatic station searching device is used, only the channels used in the region are set in each storage area, for example, in descending order of frequency.

[Problem that the invention attempts to solve]

However, for example, the
In the NTSC system, the channel spacing between channels 7 and 8 is only 4 MHz, which is particularly small compared to the other channel spacing of 6 MHz.
For this reason, when using a conventional automatic station search device in an area where channel 7 is unused and channel 8 is in use, if video signals are detected in a range of 4 MHz or more before and after each channel, channel 7 will be detected. During detection, eight channels of video signals are detected. In other words, assuming that four channels have already been set up to the seventh channel, these seven channels will be set in the fifth storage area. Of course, the 8th channel where the video signal was mistakenly detected in the 7th channel will be replaced by the next 6 channels.
stored in the th storage area. Therefore, if the fifth storage area is selected using the channel selection button or the up-down button, eight channels will be displayed with poor quality images.

In this way, conventional automatic station searching devices have the problem that when there is a narrow interval between channel frequencies and the detection range of each channel is wide, there is a risk of erroneously detecting and setting the video signal of the adjacent channel. It had a point.

[Means for solving problems]

In order to solve the above problems, this invention uses an electronic tuning circuit that can set any channel using a synthesizer method, a video detection circuit that emits a video detection signal when a video signal is detected, and an electronic tuning circuit. An automatic station searching device for a television receiver comprising a station searching means for scanning all channels and sequentially setting only the channels for which a video detection signal is emitted from a video detection circuit to an electronic tuning circuit,
An erroneous detection determination circuit that issues an erroneous detection determination signal when the difference between the frequency of the video signal from the video intermediate frequency amplification circuit and a reference frequency is within a predetermined range; In this case, the present invention is characterized in that a detection cancellation circuit is provided for canceling the video detection signal emitted from the video detection circuit.

[Effect]

When the automatic station searching device having the above configuration is used, the station searching means starts from the first channel and sequentially scans all the channels using the electronic channel selection circuit.
This scanning involves, for example, counting clock pulses to create a tuning voltage or tuning frequency one after another.
This is done by sending the signal to an electronic tuning circuit using a voltage synthesizer method or a frequency synthesizer method. In each channel, video signals are detected over a certain range of frequencies before and after the channel frequency. A video detection circuit detects the video signal. This video detection circuit includes, for example, a circuit that detects the presence or absence of a synchronization signal in a video signal. When the video detection circuit detects a video signal, it issues a video detection signal. Then, when this video detection signal is issued, the channel search means sequentially sets the channel in the electronic channel selection circuit. This channel setting is performed by storing the tuning voltage or tuning frequency corresponding to the channel in each storage area of the synthesizer type electronic tuning circuit. Note that if the frequency of each channel is divided into several bands, the band switching voltage and the like are also stored at the same time. Therefore, when setting channels using this automatic station searching device, only the channels actually used in the area are arranged, for example, in descending order of frequency. This results in
Channel settings can be automatically performed using a synthesizer method. This station searching means is constituted by, for example, a microcomputer.

However, when detecting a video signal in each channel, an erroneous detection determination circuit determines whether or not the video signal is erroneously detected. That is, this false detection determination circuit is
It is determined whether the difference between the frequency of the video signal output from the video intermediate frequency amplification circuit and a preset reference frequency is within a predetermined range. The reference frequency is selected such that the difference from the video intermediate frequency is outside a predetermined range, and the difference from the frequency of the erroneously detected video signal is within a predetermined range. The predetermined range is selected to such an extent that this determination can be made reliably.
Once the television system is determined, the cases in which erroneous detection of video signals may occur will also be determined. Therefore, it is possible to determine the reference frequency and the predetermined range based on the case where this false detection occurs. Specifically, this erroneous detection determination circuit can be constructed by, for example, shifting the original reference frequency of an automatic frequency tuning circuit (AFT circuit).

When a video signal having the video intermediate frequency as a carrier wave is correctly detected, the difference from the reference frequency is outside a predetermined range, so the erroneous detection determination circuit does not issue an erroneous detection determination signal. Therefore, the video detection signal issued by the video detection circuit becomes valid, and the station searching means sets the channel as described above.

However, if a video signal of an adjacent channel is erroneously detected during scanning of a certain channel, the video signal will not be correctly converted to the video intermediate frequency, and the frequency will be shifted by the channel interval. Therefore, the difference between the frequency of the video signal and the reference frequency falls within a predetermined range, and the erroneous detection determination circuit issues an erroneous detection determination signal. When the erroneous detection determination circuit issues an erroneous detection determination signal, the detection cancellation circuit cancels the video detection signal issued from the video detection circuit. For example, if a video detection circuit emits a video detection signal by switching its output to "H" level, this detection cancellation circuit forcibly grounds the output of this video detection circuit based on the false detection determination signal. It can be constructed by a switch circuit that can set the signal to the "L" level. When the detection cancellation circuit cancels the video detection signal, the station searching means can set the channel even though the video detection circuit has detected the video signal.

Therefore, according to the automatic station searching device of the present invention, channels in which video signals are erroneously detected can be excluded, and only channels in which correct video signals have been detected can be set in the electronic channel selection circuit.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

This embodiment describes an NTSC television receiver that employs an electronic channel selection circuit based on a frequency synthesizer system and uses a video intermediate frequency IC having an AFT circuit.

As shown in FIG. 1, the video intermediate frequency IC1 is
It has a video detection output terminal 2 and an AFT output terminal 3. The video detection output terminal 2 is an output terminal of a video detection circuit within the IC. A video buffer circuit 4 having a transistor Q1 is connected to the video detection output terminal 2, and the output of the video buffer circuit 4 is sent as a video signal A to a video amplification circuit or the like. Furthermore, a synchronous detection circuit 5 having transistors Q2, Q3, and Q4 is connected to the output of the video buffer circuit 4. The synchronous detection circuit 5 detects only the synchronous signal component from the video signal A using these transistors Q2, Q3, and Q4, and when the synchronous signal is detected, the signal becomes "H".
This circuit outputs a level synchronization detection signal B.
This synchronization detection signal B is sent to an electronic tuning circuit (not shown) to notify that a video signal has been detected. When an automatic station searching device is used, when the synchronous detection signal B is generated from the synchronous detection circuit 5, the corresponding channel is set in the electronic tuning circuit.

The AFT circuit in the video intermediate frequency IC1 is a circuit that outputs a voltage according to the difference between the frequency of the video signal from the video intermediate frequency amplification circuit and the reference frequency. In voltage synthesizer systems and other channel selection circuits, the reference voltage of this AFT circuit is set to 58.75MHz, which is the video intermediate frequency, and used as an automatic frequency tuning circuit. The AFT circuit in this case changes the output voltage with the characteristics shown in FIG. 2 as the frequency of the video signal from the video intermediate frequency amplification circuit deviates from 58.75MHz.
Then, automatic frequency tuning is performed by feeding back this output voltage as a tuning voltage to the local oscillation circuit of the electronic tuning circuit. However, in an electronic channel selection circuit that employs a frequency synthesizer method as in this embodiment, this AFT circuit is not necessary. Therefore, in this embodiment, the reference frequency is set to 56MHz by changing the resonant frequency of the LC circuit externally connected to this AFT circuit. Therefore, the voltage of the output of this AFT circuit changes with the characteristics shown in FIG. 3.

The AFT output terminal 3, which is the output terminal of this AFT circuit, is connected to a detection cancellation circuit 6 having a transistor Q5.
It is connected to the. The detection cancellation circuit 6 is a circuit in which when the output voltage of the AFT output terminal 3 exceeds a reference level, the transistor Q5 becomes conductive and the output is grounded. The output of this detection cancellation circuit 6 is connected to the output circuit of the synchronous detection circuit 5.

When scanning each channel using the automatic station searching device, if the correct channel frequency of that channel is received, the video signal A is output from the video detection output terminal 2 via the video buffer circuit 4. . Then, the synchronous detection circuit 5 detects the synchronous signal of the video signal A and outputs the synchronous detection signal B by setting the output to "H" level. Further, in the AFT circuit, since the video signal output from the video intermediate frequency amplification circuit has a frequency of 58.75 MHz, the output voltage becomes below the reference level as shown in FIG. Therefore, the transistor Q5 of the detection cancellation circuit 6 is not conductive, and the synchronous detection signal B of the synchronous detection circuit 5 is output as is. Therefore, the channel at this time is set in the electronic channel selection circuit.

However, in the NTSC system, the channel spacing is
Although the frequency is 6MHz, only the channel spacing between channel 7 and channel 8 is 4MHz. Therefore, if 8 channels are used in that area and 7 channels are unused, there is a risk that the 8 channel video signal will be erroneously detected during scanning of the 7 channels. In other words, if video signals are detected in a range of 4 MHz before and after scanning 7 channels, these 8 channels separated by 4 MHz will be received. The 8-channel video signal A is sent to the synchronous detection circuit 5, where a synchronous signal is detected in the same manner as described above, and a synchronous detection signal B is output. However, when the 8-channel video signal at this time is output from the video intermediate frequency amplification circuit, the frequency becomes 54.75MHz. Therefore, as shown in FIG. 3, the output voltage of the AFT circuit becomes equal to or higher than the reference level. As a result, when the output voltage of the AFT output terminal 3 exceeds the reference level, the transistor Q5 of the detection cancellation circuit 6 becomes conductive. When the transistor Q5 becomes conductive, the synchronous detection circuit 5 becomes “H”.
The level output is grounded and the synchronization detection signal B is canceled. Therefore, even though the synchronization signal is detected by the synchronization detection circuit 5, the electronic tuning circuit does not detect the synchronization signal.
Channel 7 at this time is not set.

As described above, in this embodiment, when an automatic station search device is used in an area where channel 7 is unused and channel 8 is used, it is possible to prevent channel 7 from being set erroneously. .

Note that, as mentioned above, the frequency synthesizer method does not require an AFT circuit. However, the video intermediate frequency IC 1 often uses parts common to voltage synthesizer systems and the like. Therefore, in the conventional frequency synthesizer system, the AFT circuit in the video intermediate frequency IC1 was not used. Therefore, by changing the reference frequency of this AFT circuit and using it as an erroneous detection determination circuit in the present invention, implementation can be made extremely easily by simply adding the detection cancellation circuit 6.

[Effect of idea]

As described above, the automatic station searching device for a television receiver according to the present invention includes an electronic tuning circuit that can set any channel using a synthesizer method, and a video detection circuit that emits a video detection signal when a video signal is detected. and a search means for scanning all channels with an electronic tuning circuit and sequentially setting only the channels for which a video detection signal has been emitted from the video detection circuit to the electronic tuning circuit. The device includes an erroneous detection determination circuit that issues an erroneous detection determination signal when the difference between the frequency of the video signal from the video intermediate frequency amplification circuit and a reference frequency is within a predetermined range; The configuration includes a detection cancellation circuit that cancels the video detection signal issued from the video detection circuit when the video detection signal is issued.

This makes it possible to eliminate erroneous detection of video signals of adjacent channels when there is a narrow interval between channel frequencies and the detection range of each channel is wide. Therefore, the channels automatically set by the automatic station searching device are only the channels in which correct video signals have been detected.

Therefore, the automatic station searching device of the television receiver of the present invention eliminates the problem of poor quality of the video of the adjacent channel being displayed when automatically set channel is selected. This has the effect of eliminating inconvenience and discomfort.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the present invention, and FIG. 1 is a circuit diagram of the main part of an automatic station searching device;
Figure 2 shows the operating characteristics when the AFT circuit is used as the original automatic frequency tuning circuit, and Figure 3 shows the operating characteristics.
FIG. 3 is an operational characteristic diagram of an AFT circuit. 1 is a video intermediate frequency IC, 5 is a synchronous detection circuit (video detection circuit), and 6 is a detection cancellation circuit.

Claims (1)

[Claim for Utility Model Registration] An electronic tuning circuit that can set any channel using a synthesizer method, a video detection circuit that emits a video detection signal when a video signal is detected, and an electronic tuning circuit that scans all channels. In an automatic station searching device for a television receiver, the automatic station searching device for a television receiver comprises a searching means that sequentially sets only the channels on which the video detection signal is emitted from the video detection circuit to the electronic tuning circuit. an erroneous detection determination circuit that emits an erroneous detection determination signal when the difference between the frequency of 1 and a reference frequency is within a predetermined range;
An automatic station search device for a television receiver, characterized in that it is provided with a detection cancellation circuit for canceling a video detection signal emitted from the video detection circuit.