JP2725270B2 - Television receiver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver, and more particularly to a television receiver having a PLL synthesizer type channel selection circuit.

[Conventional technology]

2. Description of the Related Art CATV (cable television), which distributes television signals to viewers via a transmission line such as a coaxial cable, is becoming widespread. With the development of CATV, the number of receiving channels of a television receiver tends to increase. However, in CATV broadcasting, the actual carrier frequency may be shifted from the regular carrier frequency of the channel. Therefore, with the development of CATV, there is a demand for a television receiver which can easily set a large number of reception channels and can receive a signal shifted from a regular carrier frequency.

By the way, as a channel selection circuit of a television receiver,
The PLL synthesizer type is widely used. In the PLL synthesizer type channel selection circuit, if the broadcast of each channel is always a regular carrier frequency, the channel data of each channel set in the PLL frequency divider should be set to the one corresponding to the regular carrier frequency. As a result, even if the number of channels increases, tuning can be performed instantaneously.

However, as described above, in CATV broadcasting, the actual carrier frequency may be deviated from the regular carrier frequency.Therefore, a conventional PLL synthesizer type television receiver is provided with an AFT circuit, and at the time of channel selection, A search operation is performed on a signal that deviates from the normal carrier frequency.

Thus, in the conventional PLL synthesizer type television receiver, the AFT is performed every time a tuning operation is performed.
The circuit is operated. For this reason, each time a channel is selected, it takes time to search for a received signal deviating from the normal carrier frequency, and there has been a problem that the channel cannot be selected instantaneously.

Thus, a television receiver capable of instantaneously selecting a channel even for a signal deviating from the regular carrier frequency has been proposed in Japanese Patent Application No. Sho 62.
-69993.

This is because the first tuning operation searches for the optimum tuning frequency of the received signal of each television channel, stores this tuning frequency information, and selects a tuning based on the tuning frequency information stored in the next and subsequent tuning operations. The content is to do it.

[Problems to be solved by the invention]

In the above-described prior art, if the correct tuning frequency information is always stored, the tuning operation can be performed instantaneously.

However, the voice carrier or noise of the adjacent channel is erroneously pulled in and stored as tuning frequency information, or the tuning frequency information already stored in the non-volatile memory is destroyed due to discharge or power failure of the CRT. In such a case, there is a problem that an image is not displayed even when the switch of the television receiver is turned on. Since there is no means for checking whether or not the stored tuning frequency information is correct and automatically correcting the stored tuning frequency information, the stored tuning frequency information is stored only after the image of the television receiver is no longer displayed. There has been a problem that errors and destruction of tuning frequency information cannot be recognized.

In this case, it is necessary to search for the optimum tuning frequency of the received signal of each television channel again, store the tuning frequency information, and select a channel based on the tuning frequency information. However, there is a problem that such a problem occurs, and it has been desired to solve these problems.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to automatically confirm whether or not tuning frequency information stored in advance is correct. To provide machines.

[Means for solving the problem]

According to the present invention, a tuning circuit of a PLL synthesizer system is provided, a received signal of each television channel is searched for in an initial tuning operation, and this tuning frequency information is stored in a memory. In a television receiver in which a channel is selected based on the stored tuning frequency information, it is determined whether or not the tuning frequency information of the channel to which the channel selection instruction is given is stored in the memory in advance. Means for changing the tuning frequency in the vicinity of the tuning frequency information read from the memory and detecting the presence or absence of a predetermined AFT signal when it is determined that the tuning frequency information is stored in advance. Means for selecting a channel based on the tuning frequency information when the AFT signal is detected; and searching for a correct tuning frequency when the AFT signal does not exist. Means for storing the tuning frequency information obtained by the above search in the memory.

[Action]

The tuning frequency is changed near certain tuning frequency information that is already stored, and the presence or absence of a predetermined AFT signal is confirmed. When the upper AFT signal is detected in a frequency band higher than the above-mentioned tuning frequency information and the lower AFT signal is detected in a frequency band lower than the above-mentioned tuning frequency information, the above-mentioned tuning is performed. It is determined that the frequency information is correct.

On the other hand, if the predetermined AFT signal is not detected in the upper and lower frequency bands described above, the stored tuning frequency information is determined to be incorrect, and a search and tuning operation for the correct tuning frequency are performed. Will be

That is, the upper AFT signal and the lower AFT signal are detected, and the dead zone between the upper AFT signal and the lower AFT signal is detected to perform AF detection.
T control is performed to search for a carrier frequency of the received signal that deviates from the normal carrier frequency. When a received signal shifted from the normal carrier frequency is pulled in by the AFT control, tuning frequency information based on the frequency division ratio of the frequency divider at this time is stored in the memory.

From the next channel selection, the frequency division ratio of the frequency divider is set based on this tuning frequency information, so even if the carrier frequency of the input signal deviates from the regular carrier frequency, AFT control is not performed. In addition, tuning can be performed in accordance with the shifted frequency.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

 The description will be made in the following order.

(A) Configuration and operation of television receiver (B) Contents of control operation of microcomputer (A) Configuration and operation of television receiver FIG. 1 shows the configuration of a television receiver to which the present invention is applied. It shows. In FIG. 1, a received signal from an antenna 1 is supplied to a tuner circuit 2. A signal of a desired reception channel is selected by the tuner circuit 2, and this signal is converted into a video intermediate frequency signal by a mixing circuit of the tuner circuit 2.

This television receiver employs a PLL synthesizer type channel selection circuit. That is, the local oscillation signal from the tuner circuit 2 is supplied to the phase comparator 5 via the pre-frequency divider 3 and the frequency divider 4. The reference signal is supplied from the reference signal oscillator 6 to the phase comparator 5. The phase comparator 5 compares the local oscillation output from the pre-frequency divider 3 and the frequency divider 4 with the reference signal output from the reference signal oscillator 6. The comparison output is supplied to the tuner circuit 2 via the low-pass filter 7, and the local oscillation signal is controlled based on the comparison output. The pre-frequency divider 3, the frequency divider 4, the phase comparator 5, the reference signal oscillator 6, and the low-pass filter 7 constitute a PLL 8. The frequency division ratio of the frequency divider 4 is set by the microcomputer 10 based on the channel data stored in the memory 9. At the time of the first channel selection, AFT control is performed as described later. That is,
At the time of the first tuning, the frequency division ratio of the frequency divider 4 is set so that the local oscillation frequency is close to the frequency corresponding to the normal carrier frequency. The local oscillation frequency is moved stepwise upward and downward, and AFT control is performed. When the received signal is pulled in by the AFT control, the offset data [the actual carrier frequency of each channel] based on the frequency division ratio of the frequency divider 4 at that time is stored in the memory 9. At the next channel selection, a desired reception channel is selected using the offset data stored at the time of the first channel selection.

The video intermediate frequency signal output from the tuner circuit 2 is supplied to a video detection circuit 12 via a video intermediate frequency amplification circuit 11.
Supplied to The output of the video intermediate frequency amplification circuit 11 is video-detected by the video detection circuit 12, and a composite color video signal is output from the video detection circuit 12. This composite color video signal is supplied to the input source selector 13.

The video intermediate frequency signal output from the video intermediate frequency amplification circuit 11 is supplied to the AFT detection circuit 14. AFT detection circuit
At 14, this video intermediate frequency signal is FM detected. As a result, the AFT detection circuit 14 outputs an AFT signal based on the deviation of the input signal frequency from the normal channel frequency. This AFT signal is supplied to the microcomputer 10. At the time of the first tuning, AFT control is performed using this AFT signal.

That is, first, the local oscillation frequency is set near the frequency corresponding to the normal carrier frequency. The local oscillation frequency is moved stepwise upward and downward.
In this way, the upper AFT signal and the lower AFT signal are detected, and the local oscillation frequency is set in a dead zone between the upper AFT signal and the lower AFT signal.

At this time, an audio signal or noise may be erroneously introduced. Then, the horizontal synchronizing signal is detected by the synchronizing signal detecting circuit 16, and this horizontal synchronizing signal is supplied to the microcomputer 10. The microcomputer 10 counts the number of horizontal synchronization signals per predetermined time. If the audio signal or noise is pulled in by AFT control, a predetermined number of horizontal synchronization signals are not detected in a predetermined time, so it can be determined whether the TV signal has been correctly pulled in or the audio signal or noise has been pulled in. . If the audio signal or noise has been pulled in, use AFT
Control is resumed.

Note that in CATV broadcasting, the actual carrier frequency may deviate considerably from the regular carrier frequency. So AF
A plurality of frequency points at which the detection of the T signal is started may be set, and AFT control may be performed at each frequency point to substantially widen the pull-in range.

In this way, the upper AFT signal and the lower AFT signal are detected,
By detecting the dead zone between the upper AFT signal and the lower AFT signal and performing AFT control, it is possible to pull in a received signal whose carrier frequency deviates from the normal carrier frequency. As described above, when a received signal deviating from the regular carrier frequency is pulled in by the AFT control at the time of the first channel selection, offset data based on the frequency division ratio of the frequency divider 4 at this time is stored in the memory 9.

From the next channel selection, the frequency division ratio of the frequency divider 4 is set based on the offset data. For this reason, from the next channel selection, even if the actual carrier frequency of the input signal deviates from the regular carrier frequency, the AFT control is not performed and the
Tuning can be performed in accordance with the shifted frequency.

The offset data obtained by performing the AFT control at the time of the first tuning is stored in the memory 9 even if the user does not perform the preset operation.
Tuning is performed using the offset data. Therefore, even if the number of channels increases, it is not necessary to set channel data.

In FIG. 1, 15A and 15B are external video input terminals. The television receiver is provided with the external video input terminals 15A and 15B as described above. Video devices such as a VTR and a video disk can be connected to the external video input terminals 15A and 15B. Video input terminal 15A,
A video signal from a video device (not shown) connected to 15B is supplied to the input source selector 13.

The input source selector 13 is switched by the output of the microcomputer 10 based on a command from the commander 23. Video detection circuit by input source selector 13
A desired video signal is selected from the video signal from 12 and the video signals from the external video input terminals 15A and 15B.

The composite color video signal output from the input source selector 13 is supplied to the video signal processing circuit 17, and a synchronization signal in the composite color video signal output from the input source selector 13 is detected by the synchronization signal detection circuit 16. . The detected synchronization signal is transmitted to the microcomputer 10
And the synchronization signal is supplied to the deflection circuit 18. Horizontal and vertical deflection currents are formed by the deflection circuit 18, and the horizontal and vertical deflection currents flow through the deflection coils of the cathode ray tube 19. In the video signal processing circuit 17, the three primary color signals R,
G and B are demodulated, and the three primary color signals R, G and B are added to adders 20A and 20A.
It is supplied to the cathode ray tube 19 via B and 20C, respectively.

The microcomputer 10 includes a key switch 25 and
Channel switching command from the commander 23 via the light receiving unit 24,
Various commands such as a source switching command are given. When a channel switching command is given to the microcomputer 10,
The frequency division ratio of the frequency divider 4 of the PLL 8 is reset according to the desired reception channel. When a source switching command is given to the microcomputer 10, the input source selector 13
Are switched according to the designated input source.

By the operation of the commander 23, various display commands are given from the microcomputer 10 to the display generation circuit 26. Various display signals are output from the display generation circuit 26 based on a command from the microcomputer 10. The display signals are superimposed on the three primary color signals R, G, B output from the video signal processing circuit 17 by the adders 20A, 20B, 20C, respectively. Various information such as channel information is displayed on the cathode-ray tube 19 on the display screen by the output from the display generation circuit 26.

(B) Contents of control operation of microcomputer The contents of control operation of the microcomputer 10 are shown in FIG.

That is, as shown in the flowchart of FIG. 2, when a channel is selected at the time of channel selection, it is determined whether offset data of the channel is stored in advance (step). If the offset data is stored, the offset data is read out (step), and at the same time, the tuning frequency is locked at, for example, 200 KHz higher than the offset data (step). Then, the presence or absence of the AFT-down signal "upper AFT signal" is checked (step), and if there is no AFT-down signal, the procedure goes to step, and if there is the AFT-down signal, the procedure goes to step.

In the step, the tuning frequency is locked, for example, 200 KHz lower than the offset data, and the AFT
-The presence or absence of an up signal (lower AFT signal) is confirmed. A
If there is no FT-up signal, go to step
If there is a T-up signal, go to step.

In the step, since the offset data stored in advance is determined to be correct by the processing from step to step, the synchronization frequency is accurately locked to the offset data, and there is no AFT-up signal or AFT-down signal. After confirmation, channel selection is performed based on the offset data. However, at this stage, the horizontal synchronization signal, that is, the H pulse is counted in step because there is a possibility that a noise, an audio signal or the like may be erroneously introduced.
In the step, if the counted number of H pulses does not fall within the predetermined range, go to the step. If the number falls, the offset data is correct and an erroneous signal such as an audio signal is drawn. This offset data is stored in the memory 9 because it is clear that there is no offset data. The presence or absence of the SYNC component is not limited to the number of H pulses, and may be detected.

On the other hand, if the offset data is not correctly stored in the step, AFT control, so-called wide AFT
Control is performed (step), and it is determined whether the received signal has been pulled in by the AFT control (step). When a correct received signal is received, the offset data at that time is stored (step).

In this way, it is checked in advance whether or not the offset data as tuning frequency information stored in the memory 9 is correctly tuned to the received signal of the channel, and if it is tuned, tuning is immediately performed. Will be On the other hand, when tuning is not performed, AFT control is performed again to search for a correct tuning frequency of the received signal of the channel, and this is stored as offset data and tuning is performed.

〔The invention's effect〕

According to the present invention, it is possible to automatically check whether the tuning frequency information stored in advance is correct before selecting a channel. If erroneous tuning frequency information is stored, tuning frequency information can be corrected correctly and quickly so that tuning can be performed in a short time. Thereby, there is also an effect that a problem that an image is not displayed as in the related art is solved.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a flowchart used for explaining one embodiment of the present invention. Description of main symbols in the drawings 2: tuner circuit, 4: frequency divider, 8: PLL, 10: microcomputer, 14: AFT detection circuit.

Claims (1)

(57) [Claims] 1. A tuning circuit of a PLL synthesizer system is searched, a received signal of each television channel is searched by an initial tuning operation, and tuning frequency information is stored in a memory.
In a television receiver that performs channel selection on the basis of the stored tuning frequency information, the tuning frequency information of the channel to which the channel selection instruction is given is stored in the memory in advance in the memory. Means for judging whether or not the tuning frequency information is stored in the memory, and when it is determined that the tuning frequency information is stored in advance, the tuning frequency is changed near the tuning frequency information read from the memory, and Means for detecting the presence or absence of an AFT signal, means for selecting a station based on the tuning frequency information when the AFT signal is detected, and performing search for a correct tuning frequency when the AFT signal does not exist. Means for storing tuning frequency information obtained by the search in the memory.