JPH053788B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a television receiver, and in particular, in its tuning circuit, from the time of channel selection operation to the time of pulling in an effective television broadcast signal by AFT (automatic frequency adjustment). It relates to something that avoids providing unsightly sounds and images to the viewer.

BACKGROUND TECHNOLOGY AND PROBLEMS In a television receiver, from when a channel is selected to when an effective television broadcast signal is input by the AFT circuit, there is no broadcast signal, so noise is emitted as audio. The screen also becomes unsightly. Therefore, the video signal is blanked and the audio is muted from the time the channel selection operation is performed until the valid television broadcast signal is brought in by AFT operation so as not to cause discomfort to the user. There is.

In this type of television receiver, if a valid television broadcast signal is immediately pulled in by AFT from the channel selection operation, there is no problem because the video blanking and audio muting are canceled immediately. If the AFT circuit is designed to have the ability to pull in this offset broadcast wave when the signal is offset, the AFT operation will not be able to pull in the offset broadcast signal easily, so the image will be lost for a maximum of 2 to 3 seconds. Blanking and audio muting will remain in effect. Then, these 2~
For three seconds, there will be no image or sound from the television receiver, and the user may misunderstand that the receiver has malfunctioned.

Purpose of the Invention In view of the above points, the present invention provides a television set that prevents a state in which no picture or sound is produced for a relatively long period of time from the time of channel switching, thereby eliminating the possibility that the user may misinterpret it as a malfunction. The aim is to provide a television receiver.

Summary of the Invention This invention basically performs video blanking and audio muting from the time of channel selection operation until the effective television broadcast signal is pulled in by AFT. If the broadcast signal is not being received easily, forcefully cancel video blanking and audio muting after a certain period of time that does not cause the user to feel uneasy after the channel selection operation.
This is to avoid giving the user the misunderstanding that the receiver is malfunctioning.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings, taking as an example a case in which a channel selection circuit section is configured using a microcomputer.

FIG. 1 is a system diagram of one embodiment of the present invention, in which 1 is an electronic tuning tuner, 2 is a video intermediate frequency amplification circuit,
3 is a video detection circuit; 4 is a video amplification circuit; the output of the video amplification circuit 4 is supplied to a cathode ray tube 5, and an image is displayed on the screen thereof. Further, 6 is an audio intermediate frequency amplification circuit, 7 is an audio demodulation circuit, and 8 is an audio amplification circuit.An audio signal from the audio amplification circuit 8 is supplied to a speaker 9 to reproduce audio.

10 is a microcomputer, 11 is its
12 is a ROM, 13 is a RAM, 14 is a system bus, and 15 is a timer. The timer 15 may use the timer function of the microcomputer 10 itself.

Reference numeral 20 denotes a receiver for transmitting signals from the remote controller, such as infrared rays.The received remote control signal is supplied to a remote control receiving circuit 21 having a decoder and decoded, and the decoded output is sent to the system bus 14 via an interface 31. transmitted to. 22 is a key device, and when a channel selection key is operated, a signal corresponding to the operated key is obtained, and this signal is transmitted to the system bus 14 via the interface 32.

Reference numeral 23 denotes a channel selection voltage generation circuit, which generates a voltage when a channel selection key is operated on the key device 22 or when a channel selection signal is supplied to the remote control receiving circuit 21 as a remote control signal.
The channel selection information signal is supplied to the selection voltage generation circuit 23 through the interface 33, and the selection voltage corresponding to the selected channel is obtained from the selection voltage generation circuit 23. is supplied to the tuner 1, the local oscillation frequency from the local oscillation circuit is controlled, and a tuning operation is performed.

24 is an AFT circuit, and video intermediate frequency amplification circuit 2
The carrier wave component of the video intermediate frequency signal is extracted from the signal from the signal, and this is subjected to FM detection to obtain the AFT voltage. Then, from this AFT circuit 24,
The AFT voltage is supplied to the channel selection voltage generation circuit 23,
This finely adjusts the channel selection voltage. Also, this
The signal from the AFT circuit 24 is sent to the interface 3.
4 to the system bus 14, and the microcomputer 10 determines whether or not a television broadcast signal has been received by AFT.

Further, 25 is a blanking/mutating signal supply circuit, and when a command to start blanking and mutating is given from the system bus 14 through the interface 35, the output signal MS from this becomes "1", indicating the end. When a command is given, this signal MS is set to "0". Then, this signal MS is supplied to the video amplification circuit 4 and the audio amplification circuit 8, and this signal
During the MS "1" period, the video is blanked,
The sound is muted, no image is displayed on the screen, and no sound is output.

In the television receiver configured as described above, the operations shown in the flowchart of FIG. 2 are performed in accordance with the program stored in the ROM 12 when selecting a channel.

The operation will be explained below with reference to this flowchart.

First, for example, when the key switch is turned on in the key device 22 and a channel selection operation is performed (step [101]), the output signal MS of the blanking/mutating signal generation circuit 25 rises to "1", and the video blanking and It becomes an audio muting operation and there is no picture or sound. At the same time, the timer 15 is reset by the channel selection operation (step [102]).

Thereafter, a tuning voltage corresponding to the selected channel is supplied from the tuning voltage generating circuit 23 to the tuner 1, and a tuning operation is performed (step [103]).
Then, the AFT voltage is obtained from the AFT circuit 24, and an AFT operation is performed to finely adjust the channel selection voltage (step [104]). The signal from this AFT circuit 24 is then monitored to determine whether there is a broadcast signal in a predetermined frequency range corresponding to the AFT pull-in range (step [105]).

When there is a broadcast signal in the specified frequency range, that is, when the broadcast signal is pulled in by AFT,
Blanking/mutating signal generation circuit 25
A blanking and muting release command is given, and the output signal MS becomes "0" (step [106]), and an image appears on the screen and audio is output.

When there is no broadcast signal in the specified frequency range,
In other words, when AFT does not pull in a broadcast signal,
Timer 15 is advanced (step [107]).
Then, based on the time of the timer 15, it is determined whether or not a period of time such as 500 msec or more has elapsed since the channel selection operation so that the user does not feel uneasy due to no picture or sound (step [108]). .

If 500 msec has not elapsed, AFT operation (step [104]) is performed, and it is determined again whether or not a broadcast signal exists in the predetermined frequency range. If there is, the process moves to step [106]; if not, The process moves to step [107] and timer 15 is further advanced.

Then, if it is determined from the timer 15 that 500 msec or more has elapsed, the process goes to step [108].
Moving on to step [106], video blanking and audio muting are canceled even when the broadcast signal is not within the predetermined frequency range, that is, even when an effective television broadcast signal is not brought in by AFT.

Then, an image of the noise is displayed on the screen and the noise is emitted as audio. Therefore, the user will be able to detect that the broadcast signal is not being received and will not be mistaken that the receiver is malfunctioning.

In this example, even after forced blanking and muting are canceled, the AFT operation continues until a broadcast signal is received.

The above example was explained assuming that the AFT is difficult to apply because the broadcast wave signal is offset, but the broadcast wave signal is a weak signal that is judged to be no signal by the tuning circuit. This invention can also be applied to certain cases. In this case,
When 500msec or more has passed without AFT being applied,
The AFT operation may also be stopped when mutating etc. are canceled. Here, detection of whether the received signal is a weak signal can be performed, for example, in an AGC circuit.

In this case, when the AFT operation is stopped, images and sounds are obtained with weak signals, so for example, in a television receiver that uses a rod antenna, it is necessary to adjust the direction of the rod antenna to find the optimal reception direction for the broadcast signal. can be determined.

Effects of the Invention According to the present invention, when a broadcast signal is not pulled in by AFT operation for a certain period of time after channel selection operation, video blanking and audio muting are forcibly canceled, so that the user can There is no need to worry about confusing it with a malfunction.

Therefore, assuming that the broadcast signal is offset, an AFT circuit that can also draw in the offset broadcast signal can be used without any problem.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an example of a television receiver according to the present invention, and FIG. 2 is a flowchart for explaining its operation. 10 is a microcomputer, 22 is a key device, 23 is a tuning voltage generation circuit, 24 is an AFT circuit,
25 is a blanking/mutating signal supply circuit.

Claims (1)

[Scope of Claims] 1. An automatic frequency adjustment circuit, a microcomputer that uses the automatic frequency adjustment circuit to determine the acquisition state of an effective television signal, and a video signal system from a blanking and muting signal generation circuit based on the microcomputer. In a television receiver configured to blank and mute the channel and audio signal path, automatic frequency adjustment is performed by channel selection operation, and an effective television signal is drawn in from the automatic frequency adjustment circuit. When the blanking and mutating signal generation circuit supplies the blanking and mutating end signal to the video signal path and the audio signal path,
When the microcomputer determines that no effective television signal is drawn in from the automatic frequency adjustment circuit for a certain period of time after the channel selection operation, the blanking and muting signal generation circuit controls the video signal path and the audio signal system. A television receiver characterized in that a blanking and muting end signal is supplied to the television receiver.