JPS63234778A - Television receiver - Google Patents

Abstract

PURPOSE:To select a channel to a signal deviated from a normal frequency by executing an AFT control at the time of an initial channel selection, storing offset channel data, and selecting the channel by the use of the offset channel data at the time of selecting the channel after the initial channel selection. CONSTITUTION:At the time of the initial channel selection, the AFT signal of an upper side and the AFT signal of a lower side are detected, a dead band between the AFT signal of the upper side and the AFT signal of the lower side is detected to execute the AFT control, thereby, a receiving signal in which a carrier frequency is deviated from the normal frequency can be pulled in. Then, when the receiving signal in which the carrier frequency is deviated from the normal frequency at the time of the initial channel selection is pulled in according to the AFT control, the offset channel data based on the frequency dividing ratio of a frequency divider 4 at this time is stored in a memory 9. From a next channel selection, the frequency dividing ratio of the frequency divider 4 is set based on this offset channel data. Therefore, from the next channel selection, even when the carrier frequency of an input signal is deviated from the normal frequency, the channel can be selected correspondingly to the deviated frequency without executing the AFT control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a television receiver having a PLL synthesizer system circuit.

[Summary of the invention]

In a television receiver having a PLL synthesizer system circuit, the present invention searches for an optimal tuning frequency having an offset with respect to a predetermined frequency of each television channel in an initial tuning operation, and stores this tuning frequency information. However, by making the next tuning operation based on this memorized tuning frequency information, it is now possible to tune instantly even for signals that deviate from the normal frequency. It is something.

[Conventional technology]

CATV (cable television), which distributes television signals to viewers through transmission lines such as coaxial cables, is becoming popular. With the development of CATV, the number of channels that television receivers can receive is increasing. Also, C
In ATV broadcasts, the carrier frequency may deviate from the regular carrier frequency of the channel. therefore,
With the development of CATV, there is a need for a television receiver that can easily set a large number of reception channels and that can receive signals that are deviated from the regular carrier frequency.

PLL synthesizer type circuits are widely used as channel selection circuits for television receivers. In the PLL synthesizer type channel selection circuit, if the broadcast of each channel is always at the regular frequency, by setting the channel data of each channel in the PLL0 frequency divider to correspond 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 when selecting a channel, a search operation is performed for a signal that deviates from the regular carrier frequency.

[Problem that the invention seeks to solve]

As described above, the conventional PLL synthesizer type television receiver is provided with an AFT circuit, and the AFT circuit is operated at the start of a channel selection operation. Therefore, when selecting a channel, it takes time to search for a received signal that deviates from the normal frequency, and there is a problem in that instantaneous channel selection cannot be performed.

Therefore, an object of the present invention is to provide a television receiver that can instantly select a channel even for a signal that deviates from the regular carrier frequency.

[Means for solving problems]

In a television receiver having a PLL synthesizer type channel selection circuit, the present invention searches for the optimal tuning frequency of the received signal of each television channel in the first tuning operation, stores this tuning frequency information, and stores the tuning frequency information for subsequent use. This is a television receiver that selects a channel based on tuning frequency information stored during a channel selection operation.

[Effect]

When tuning for the first time, the upper AFT signal and the lower AFT signal are detected, the dead zone between the upper AFT signal and the lower AFT signal is detected, AFT control is performed, and the carrier frequency is set to the normal frequency. A search is made for received signals that are off-frequency. Is the received signal that deviates from the regular frequency when tuning for the first time due to AFT system? When the signal is pulled in by ffj, 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 time of channel selection, the frequency division ratio of the frequency divider 4 is set based on this offset channel data. For this reason,
From the next time of tuning, even if the carrier frequency of the input signal deviates from the normal frequency, tuning can be performed in response to this deviated frequency without performing AFT control.

〔Example〕

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

FIG. 1 shows the 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. In FIG. A tuner circuit 2 selects a signal of a desired reception channel, and a mixing circuit of the tuner circuit 2 converts this signal into a video intermediate frequency signal.

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 prefrequency divider 3 and the frequency divider 4. A reference signal is supplied to the phase comparator 5 from a reference signal oscillator 6 . The phase comparator 5 compares the local oscillation output passed through the prefrequency divider 3 and the frequency divider 4 with the reference signal output from the reference signal oscillator 6. This comparison output is supplied to the tuner circuit 2 via the low-pass filter 7, and the local oscillation signal is controlled based on this comparison output. These prescaler 3, divider 4
, a phase comparator 5, a reference signal oscillator 6, and a low-pass filter 7 constitute a PLL 8. The frequency division ratio of the frequency divider 4 is set by the microcomputer IO based on the channel data stored in the memory 9. When selecting a channel for the first time, AFT control is performed as described later. That is, when tuning for the first time, the frequency division ratio of the frequency divider 4 is set so that when the local oscillation frequency is the normal frequency, it becomes close to the corresponding frequency. AFT control is performed by moving the local oscillation frequency upward and downward like a steering knob. AFT
When the received signal is pulled in by control, the frequency divider 4 at that time
Offset channel data based on the frequency division ratio is stored in the memory 9. During the next channel selection, the desired reception channel is selected using the offset channel data obtained during the first channel selection.

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

Further, the video intermediate frequency signal output from the video intermediate frequency amplification circuit 11 is supplied to the AFT detection circuit 14. AFT
The detection circuit 14 converts this video intermediate frequency signal into an FM transverse wave. As a result, the AFT circuit 14 outputs an <AFT signal based on the deviation of the human input signal frequency with respect to the normal channel frequency. This AFT signal is supplied to the microcomputer 10. When tuning for the first time, AFT control is performed using this AFT signal.

That is, first, when the local oscillation frequency is a normal frequency, it is set near the corresponding frequency. This local oscillation frequency is moved upward and downward in steps. In this way, the upper AFT signal and the lower AFT signal are detected, and the local oscillation frequency is set in the dead zone between the upper AFT signal and the lower AFT signal.

At this time, audio signals and noise may be accidentally introduced. Therefore, a horizontal synchronizing signal is detected by the synchronizing signal detection circuit 16, and this horizontal synchronizing signal is supplied to the microcomputer IO.

The microcomputer 10 counts the number of horizontal synchronization signals per predetermined time. AFTil audio signals and noise
l? If the signal is pulled in due to II, a predetermined number of horizontal synchronization signals are not detected within a predetermined time.

This allows you to check whether the television signal was correctly drawn in or not.
It is determined whether audio signals or noise have been introduced. If audio signals or noise have been drawn in, AFT control is performed again.

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

When selecting a channel for the first time, the upper ΔFT signal and the lower AFT signal are detected in this way, and the upper AFT signal and the lower AF signal are detected.
By detecting the dead zone with the T signal and performing AFT control, it is possible to draw in a received signal whose carrier frequency deviates from the normal frequency. As mentioned above, the received signal that deviates from the normal frequency at the time of initial tuning is AFT.
When the signal is pulled in by control, offset channel data based on the division of the frequency divider 4 at this time is stored in the memory 9.

From the next channel selection, the minute ratio of the frequency divider 4 is set based on this offset channel data. For this reason,
From the next time of tuning, even if the carrier frequency of the input signal deviates from the normal frequency, tuning can be performed in response to this deviated frequency without performing AFT control.

Note that the offset channel data obtained by performing AFT control during the first channel selection will be stored in the memory 9 even if the user does not perform any presetting operations, and from the next channel selection onwards, the offset channel data will be stored in the memory 9 without any special presetting by the user. (In both cases, channel selection is performed using this offset channel data. Therefore, even if the number of channels increases, there is no need to set channel data.

That is, as shown in the flowchart of FIG. 2, when a channel number is specified during channel selection, it is determined whether offset channel data for that channel is stored in advance (step 2). If offset channel name day/evening is not memorized, A, F T
Control is performed (step ■), and it is determined whether the received signal has been acquired by 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 step (2), the offset channel data of that channel is read out (step (2)), and a channel is selected based on this offset channel data (step (2)).

In this way, AFT control is performed for the first channel selection, the channel data at this time is stored, and the next time and subsequent channel selections are performed using this offset channel data. Therefore, from the next time of tuning on a signal whose normal carrier frequency has shifted, tuning can be performed without performing AFT control, and the tuning time can be shortened.

In FIG. 1, 15A and 15B are external video input terminals. This television receiver is thus provided with external video input terminals 15A and 15B. Video equipment such as a VTR or video disc can be connected to the external video input terminals 15A and 15B. Video signals from video equipment connected to external video input terminals 15A and 15B are supplied to 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. The input source selector 13 selects the video signal from the video detection circuit 12 and the external input terminal 15A,
A desired video signal is selected from among the video signals from 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 a synchronization signal detection circuit 16. This detected synchronization signal is supplied to the microcomputer 10, and this synchronization signal is also supplied to the deflection circuit 1.
8. Horizontal and vertical deflection currents are formed in the deflection circuit 18, and these horizontal and vertical deflection currents are applied to the cathode ray tube 1.
9 deflection coil. The video signal processing circuit 17 demodulates the three primary color signals R, GSB, and the three primary color signals R,
G and B are supplied to the cathode ray tube 19 via adders 20A, 20B, and 20C, respectively.

Various commands such as channel switching commands and source switching commands are given to the microcomputer 10 from the key switch 25 and the commander 23 via the light receiving section 24. 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 to correspond to the desired reception channel. Further, when a source switching command is given to the microcomputer 10, the input source selector 13 is switched according to the specified input source.

By operation of the commander 23, the microcomputer 10
Various display commands are given to the display generation circuit 26 from the display generating circuit 26.

Various display signals are output from the display generation circuit 26 based on instructions from the microcomputer 1o. This display signal is superimposed on the three primary color signals R, G, and B output from the video signal processing circuit 17 by adders 2°A, 20B, and 20C, respectively. With the output from this display generation circuit 26,
Various information such as channel information is displayed on the cathode ray tube 19.

〔Effect of the invention〕

According to this invention, AFT control is performed for the first channel selection, and offset channel data at this time is stored. When selecting a channel from the next time onwards, this offset channel data is used to select a channel.

Therefore, it is possible to instantly select a channel even for a signal that deviates from the normal frequency.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a flowchart used to explain the embodiment of the invention. Explanation of main symbols in the drawings 2: Tuner circuit, 4: Frequency divider, 8: PLL, 10
: Microcomputer, 14 : AFT detection circuit. Agent Patent Attorney Masato Sugiura Figure 2

Claims (1)

[Claims] In a television receiver having a PLL synthesizer type channel selection circuit, the optimum tuning frequency of the received signal of each television channel is searched for in the first tuning operation, this tuning frequency information is stored, and the tuning frequency information is stored for the next time. A television receiver configured to select a channel based on the stored tuning frequency information in subsequent channel selection operations.