JP2570284B2 - TV receiver - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a television receiver having a PLL synthesizer type tuning circuit.

[Summary of the Invention]

According to the present invention, in a television receiver having a PLL synthesizer type channel selection circuit, an optimum synchronization frequency having an offset with respect to a predetermined frequency of each television channel is searched by an initial channel selection operation, and this tuning frequency information is stored. Then, in the next and subsequent tuning operations, tuning is performed based on the stored tuning frequency information, so that even a signal deviating from the normal frequency can be instantly selected. Things.

[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 is increasing. In CATV broadcasting, the carrier frequency may be shifted from the normal carrier frequency of the channel. Therefore, with the development of CATV, there is a demand for a television receiver that can easily set a large number of reception channels and can receive a signal shifted from a regular carrier frequency.

As a channel selection circuit of a television receiver, a PLL synthesizer type is widely used. In the PLL synthesizer type tuning circuit, if the broadcast of each channel is always the regular frequency, the channel data of each channel set in the PLL divider should be set to the one corresponding to the regular frequency. Even if the number of channels increases, it is possible to select a channel instantly.

However, as described above, in CATV broadcasting, the carrier frequency may deviate from the regular frequency. For this reason,
A conventional PLL synthesizer type television receiver is provided with an AFT circuit, and performs a search operation on a signal that is deviated from a regular carrier frequency at the time of channel selection.

[Problems to be solved by the invention]

As described above, the conventional PLL synthesizer television receiver is provided with the AFT circuit, and the AFT circuit is operated at the start of the channel selection operation. For this reason, it takes time to search for a received signal deviating from the regular frequency at the time of tuning, and there is a problem that tuning cannot be performed instantaneously.

Therefore, an object of the present invention is to provide a television receiver which can instantaneously select a channel even for a signal deviating from a normal carrier frequency.

[Means for solving the problem]

According to the present invention, in a television receiver having a PLL synthesizer type channel selection circuit, an optimum tuning frequency of a received signal of each television channel is searched by an initial channel selection operation, and this tuning frequency information is stored. This is a television receiver that performs channel selection based on tuning frequency information stored in a channel selection operation.

[Action]

At the time of the first tuning, the upper AFT signal and the lower AFT signal are detected, a dead zone between the upper AFT signal and the lower AFT signal is detected, AFT control is performed, and the carrier frequency is adjusted to a normal frequency. The received signal deviated from the frequency is searched. When a received signal deviating from the normal frequency is pulled in by the AFT control at the time of the first channel selection, offset channel 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 division ratio of the frequency divider 4 is set based on the offset channel data. For this reason, from the next channel selection, even if the carrier frequency of the input signal deviates from the normal frequency, the channel can be tuned in accordance with the deviated frequency without performing the AFT control.

〔Example〕

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

FIG. 1 shows a configuration of a television receiver to which the present invention is applied. 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 dividing ratio of the 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 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 channel data 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 channel data stored at the time of the first channel selection.

The video intermediate frequency signal output from the tuner circuit 2 is
It is supplied to a video detection circuit 12 via a video intermediate frequency amplification circuit 11. Video detection circuit 12 and video intermediate frequency amplification circuit 11
Is output, and the 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 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 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,
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. When an audio signal or noise is introduced by AFT control, a predetermined number of horizontal synchronization signals are not detected in a predetermined time.
As a result, the television signal was correctly pulled in,
It is determined whether an audio signal or noise has been pulled in. If an audio signal or noise has been pulled in, AFT control is performed again.

It should be noted that, in CATV broadcasting, there is a case where the frequency is considerably shifted from the carrier frequency. Therefore, a plurality of frequency points at which the detection of the AFT signal is started may be set, and AFT control may be performed at each frequency point to substantially increase the pull-in range.

At the time of the first channel selection, the upper AFT signal and the lower AFT signal are detected in this way, the dead zone between the upper AFT signal and the lower AFT signal is detected, and the AFT control is performed. A received signal whose carrier frequency deviates from the normal frequency can be received. As described above, when a received signal deviating from the normal frequency is pulled in by the AFT control at the time of the first channel selection, the offset channel data based on the division ratio of the frequency divider 4 at this time is stored in the memory 9.

From the next channel selection, the division ratio of the frequency divider 4 is set based on the offset channel data. For this reason, from the next channel selection, even if the carrier frequency of the input signal deviates from the normal frequency, the channel can be tuned in accordance with the deviated frequency without performing the AFT control.

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

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 channel data of the channel is stored in advance (step). If the offset channel data is not stored, AFT control is performed (step), and it is determined whether the received signal has been pulled in by the AFT control (step). When the received signal is received, the offset channel data at that time is stored (step).

If the offset channel data is stored in the step, the offset channel data of that channel is read out (step), and a channel is selected based on the offset channel data (step).

As described above, the AFT control is performed for the first channel selection for the channel, the channel data at this time is stored, and the channel selection is performed using the offset channel data for the next and subsequent channel selections. For this reason, for a signal that deviates from the normal carrier frequency, tuning can be performed without performing AFT control from the next tuning, thereby shortening the tuning time.

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 equipment such as a VTR and a video disc can be connected to the external video input terminals 15A and 15B. External video input terminal 15
A video signal from a video device connected to A and 15B is supplied to an 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 external 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. The three primary color signals R, G, and B are demodulated by the video signal processing circuit 17, and the three primary color signals R, G, and B are supplied to the CRT 19 via adders 20A, 20B, and 20C, respectively.

The microcomputer 10 receives various commands such as a channel switching command and a source switching command from the key switch 25 and the commander 23 via the light receiving unit 24. When a channel switching command is given to the microcomputer 10, the PL
The frequency division ratio of the L8 frequency divider 4 is reset according to the desired reception channel. When a source switching command is given to the microcomputer 10, the input source selector 13 is 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. This display signal is 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.

〔The invention's effect〕

According to the present invention, AFT control is performed at the time of the first channel selection for the channel, and offset channel data at this time is stored. At the time of the next channel selection, channel selection is performed using the offset channel data.
For this reason, it is possible to instantaneously select a channel even for a signal deviating from the regular frequency.

[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 television receiver having a PLL synthesizer type channel selection circuit, comprising a memory for storing channel data for channel selection, and receiving a broadcast signal deviating from a regular frequency in the memory at the time of channel selection. If the offset channel data is not stored in the memory, the AFT operation is performed to obtain the offset channel data, and the obtained offset channel data is stored in the memory. Is a television receiver which reads out the offset channel data from the memory to select a channel.