JPH0210675Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic channel selection device suitable for use as a channel selection device for a television receiver, for example.

Conventionally, for example, a channel selection device for a television receiver, as shown in FIG. 1, has been proposed. In FIG. 1, reference numeral 1 denotes an electronic tuner, and the electronic tuner 1 outputs an intermediate frequency signal VIF of a selected station, and supplies it to an intermediate frequency amplification circuit 7.

A control signal S _AGC for automatic gain control (AGC) is output to a terminal 7a of this intermediate frequency amplification circuit 7.
This control signal S _AGC is applied to terminal 1e of electronic tuner 1 after initial bias is set by resistors 8 and 9.
is supplied to In the electronic tuner 1, its gain is controlled according to the control signal S _AGC supplied to the terminal 1e. For example, in the case of a strong electric field, the gain is lowered, and in the case of a weak electric field, the gain is increased.

Furthermore, the terminals 1a, 1b and 1 of the electronic tuner 1
For example, a positive DC voltage +B is supplied to c, and the mode of the electronic tuner 1 is switched to VHF low channel, high channel, and UHF, respectively. This switching is performed by key operation on the key input device 2, for example, and by signals output to the output terminals 3a, 3b, and 3c of the control circuit 3.
and 4U is controlled to be turned on and off. That is, when the VHF low channel, high channel, and UHF modes are selected, the transistors 4H, 4L, and 4U are turned on, respectively, and at this time, the terminals 1a, 1b, and 1c of the electronic tuner 1 are turned on.
+B is supplied to the terminal, and switching is performed.

Further, a voltage corresponding to the reception frequency is supplied to the terminal 1d of the electronic tuner 1 as a control voltage. This control voltage Vc is applied to a variable capacitance diode constituting a tuning circuit of this electronic tuner 1, so that its capacitance is controlled and the tuning frequency is controlled. This control voltage Vc is the output terminal 3 of the control circuit 3.
The pulse signal Pv obtained at d is amplified by the npn transistor 5 and then integrated by the integrating circuit 6.

In this case, the duty of the pulse signal Pv is varied, for example, from 0 to 100%.
Therefore, by changing the duty of this pulse signal Pv, the control voltage can be changed accordingly.
Tuning operation is performed by changing Vc and thereby changing the tuning frequency. In this case, the duty of the pulse signal Pv is automatically changed and sequentially changed at a constant rate to perform an automatic channel selection operation, so-called search.

The control circuit 3 is supplied with a synchronization detection signal Ssync for detecting the presence or absence of a synchronization signal, that is, the presence or absence of a station signal, and an AFT signal S _AFT for automatic fine adjustment (AFT) to enable station detection. ing. For example, when a station is present, the AFT signal S _AFT becomes an S-shaped signal, that is, a signal containing an up signal and a down signal, as shown in Figure 2B, and when the signal level is above a predetermined level, synchronization occurs. The detection signal Ssync is at high level "1" as shown in Figure 2A.
becomes.

Therefore, when a search is performed by sequentially changing the tuning frequency, the existence of the station is recognized in the control circuit 3 from the synchronization detection signal Ssync and the AFT signal S _AFT , and the search is then stopped.
That is, the change in duty of the pulse signal Pv is stopped, and that station is selected.

When selecting a different station next time, the change in the duty of the pulse signal Pv is continued again by key operation on the key input device 2.

Further, in this FIG. 1, 70 indicates a memory, and this memory 70 contains station information of the selected station,
For example, the pulse signal Pv for selecting that station
Information that determines the duty is written. In other words, it is possible to make presets. There are two modes for presetting: a so-called auto-preset mode, in which a station is selected by searching for one position each time the user operates a key, and the station information for that station is written; Then, the station will be selected by search and the station information for that station will be written.
For example, it can be used in both a so-called full auto preset mode, which is repeated for all positions from the low end of VHF to the high end of UHF.
In this case, in the fully automatic preset mode, the user does not have to do much presetting.

Once preset, the channel selection operation is performed by reading the desired station information from the memory 70 by key operation. Then, for example, the pulse signal Pv
The duty is determined according to the read station information, and the desired station is immediately selected.

Now, in such a conventional automatic channel selection device, as mentioned above, the AFT signal S _AFT becomes an S-shaped signal, that is, a signal including an up signal and a down signal, as shown in FIG. 2B, and the synchronization detection signal Ssync
As shown in FIG. 2A, the station is detected and selected based on the fact that the signal becomes a high level "1". Therefore, even if there is a spurious signal generated in the electronic tuner 1 in the case of a strong electric field, or a weak electric field signal from a distant station, as long as the above-mentioned conditions are satisfied, the search will be stopped and the channel will be selected. . The images at this time generally have poor reception conditions and are unsightly.

By the way, when presetting, in the auto preset mode, as mentioned above, each time the user operates a key, a station is selected by searching for one position, and that station is selected. Since station information is written, if a station with a spurious or weak electric field signal is selected as described above, you can not preset that station by performing an additional key operation, or if the reception condition is poor. You can also preset it if you want to see it. However, when presetting is performed in the fully automatic preset mode, as mentioned above, when the user performs a key operation once, the station information of the station selected by search is written, for example, VHF. from the low end of
Since this is repeated for all positions up to the high end of UHF, even if a station with a spurious or weak electric field signal is selected, it will be preset indiscriminately. In other words,
When presetting in full auto preset mode, it is convenient because the user does not have to do much presetting, but in this way even stations with spurious or weak electric field signals, that is, unnecessary stations, may be preset. There was an inconvenience.

In view of this point, the present invention is designed to prevent unnecessary stations from being preset as described above during full auto preset.

An embodiment of the automatic channel selection device according to the present invention will be described below with reference to FIG. In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 3, reference numeral 10 denotes an NPN transistor for gain control of the electronic tuner 1. The emitter of this transistor 10 is grounded, and the collector is connected to the midpoint between resistors 8 and 9 via a variable resistor 11. Connected. In this case, the resistance value of the variable resistor 11 is set such that when the transistor 10 is turned on, the initial bias of the AGC signal S _AGC is such that the gain of the electronic tuner 1 is reduced by a predetermined level, for example, 10 dB. The value can be determined as follows. For example, resistors 8 and 9 are 82KΩ and 33K respectively.
Ω, the variable resistor 11 is set to 40KΩ. Further, a control signal S _C is supplied to the base of this transistor 10 from a terminal 12 . This control signal S _C is a signal that has a low level "0" during auto preset and a high level "1" during full auto preset.

In addition, in FIG. 3, a horizontal synchronization signal P _H having a level corresponding to the electric field strength obtained from a synchronization separation circuit (not shown) is supplied to the terminal 13.
This horizontal synchronizing signal P _H is transmitted to npn via the resonant circuit 14.
is supplied to the base of a type transistor 15. In this case, the resonant frequency of the resonant circuit 14 is selected to be approximately 1/the pulse width of the horizontal synchronizing signal P _H , so that the noise on the horizontal synchronizing signal P _H is removed in this resonant circuit 14. being done.

Also, power supply terminal 1 to which positive DC voltage +B is supplied
6 is connected to a power supply terminal 20 to which a negative DC voltage -B' is supplied through a series circuit to resistors 17, 18, and 19 for setting the base bias of the transistor 15, and a midpoint connected to the resistors 18 and 19; The voltage obtained at transistor 15 serves as base bias.
supplied to the base of Also resistors 17 and 18
The midpoint of the connection is connected to the collector of an npn type transistor 21 for base bias control of this transistor 15, and the emitter of this transistor 21 is connected to the power supply terminal 16. The base of this transistor 21 is supplied with the above-mentioned control signal S _C from the terminal 12, and its on/off is controlled.

When this transistor 21 is off, the base bias of the transistor 15 becomes the voltage V _OFF divided by the resistors 17, 18 and 19, and when this transistor 21 is on, the base bias of the transistor 15 becomes the voltage V OFF.
The base bias of No. 5 is a voltage V _ON (>V _OFF ) divided by resistors 18 and 19.

In this case, when the base bias is V _ON , the level of the horizontal synchronization signal P _H supplied from terminal 13 is
Transistor 1 at Vth ₁ or more (weak electric field to strong electric field)
These V ON and V _{OFF are set so that when the base bias is V OFF} , the transistor ₁₅ is turned on when its level is Vth _{2 (} >Vth ₁ ) or higher (medium electric field to strong electric field). The value of is being sought.

Further, the emitter of the transistor 15 is grounded via a diode, and its collector is connected to a resistor 22.
It is connected to the power supply terminal 16 via a resistor 23 and a capacitor 24, and is grounded via a series circuit of a resistor 23 and a capacitor 24. A midpoint A between the resistor 23 and the capacitor 24 is connected to the power supply terminal 20 via a series circuit of resistors 25 and 26, and a midpoint A between the resistors 25 and 26 is connected to the npn transistor 2.
Connected to the base of 7. In this case, resistor 22
If the resistance values of and 23 are R ₂₂ and R ₂₃ respectively, then R ₂₂ ≫
During the pulse width period of the horizontal synchronizing signal P _H when the transistor 15 is set to R ₂₃ and the transistor 15 is turned on, the connection midpoint A
The voltage is set so that the voltage is sufficiently reduced.

When the level of the horizontal synchronizing signal P _H exceeds a predetermined level and the transistor 15 is turned on, the transistor 27 is turned off. Incidentally, when the level of the horizontal synchronizing signal P _H is lower than a predetermined level, this transistor 1
5 is off, the voltage at point A is sufficiently high, and transistor 27 remains on.

Further, the emitter of the transistor 27 is grounded, the collector thereof is connected to the power supply terminal 16 via the resistor 28, and the transistor 27
An output terminal 29 from which a synchronization detection signal Ssync is obtained is led out from the collector of .

The synchronization detection signal Ssync obtained at the output terminal 29 is supplied to the channel selection device 3 together with the AFT signal S _AFT as described above.

The rest of the structure is the same as the example shown in FIG.

In this example, a control signal S C is connected to the base of the transistor 10 from the terminal 12, as shown in _FIG.
is supplied, so the transistor 10 is turned off during auto preset and turned on during full auto preset. Therefore, during full auto preset, the gain of electronic tuner 1 is lowered by a predetermined level, for example, 10 dB.

Similarly, the control signal S _C is supplied to the base of the transistor 21 from the terminal 12, so the transistor 21 is turned on and off during auto preset.
Turns off during full auto preset. Therefore, the base bias of the transistor 15 is V _ON during auto preset, and V _OFF (<V _ON ) during full auto preset. Therefore, as shown in FIG. 4B, during auto preset, the transistor 15 is turned on when the level of the horizontal synchronizing signal P _H is Vth ₁ or more (weak electric field to strong electric field), whereas in full auto When presetting, the level is Vth ₂ or higher (medium electric field to strong electric field)
At this time, the transistor 27 is turned off and the synchronization detection signal Ssync obtained at the output terminal 29 becomes high level "1" as shown by the solid line in FIG. 4C. As a result, according to this example, the signal detection sensitivity of the horizontal synchronization signal P _H during full auto preset is higher than that during auto preset.
The signal detection sensitivity of the station is reduced.

For example, in this case, the level of the horizontal synchronizing signal P _H in a weak electric field is Vth ₁ as shown by the broken line in Figure 4B.
Vth ₂ , synchronization detection signal Ssync
As shown by the broken line in Figure 4C, during auto preset, the signal becomes high level "1" and the station signal is detected, whereas during full auto preset, it becomes low level "0" and the station signal is detected. signal is not detected.

As is clear from the embodiments described above, according to the automatic channel selection device according to the present invention, the signal detection sensitivity is reduced during full auto preset, so that the Channel selection can only be made within the range of . Therefore, a station with a weak electric field and a weak signal, for example, a distant station, will not be selected, and a weak electric field and a weak station with a weak signal will not be preset.

Moreover, according to the automatic channel selection device according to the present invention,
Since the gain of the electronic tuner is lowered during full auto preset, spurious signals are less likely to occur in the electronic tuner when the electric field is weak. Therefore, during this full auto preset, the inconvenience that channel selection is performed due to spurious signals and this is preset does not occur.

Furthermore, during full auto preset,
Since the gain of the electronic tuner is lowered, the weak electric field is made even weaker, so the above-mentioned problem of selecting and presetting a station with a weak signal due to a weak electric field is completely prevented. .

In the end, the automatic channel selection device according to the present invention does not preset unnecessary stations during full auto preset, unlike in the past, and can fully bring out the full potential of the full auto preset function. be.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of a conventional automatic channel selection device, FIG. 2 is a diagram for explaining the example in FIG. 1, and FIG.
The figure is a block diagram showing an embodiment of the automatic channel selection device according to the present invention, and FIG. 4 is a diagram for explaining the present invention. 1 is an electronic tuner, 7 is an intermediate frequency amplification circuit,
8, 9, 17, 18 and 19 are resistors, 1
0, 15, 21 and 27 are transistors, 1
1 is a variable resistor, and 29 is an output terminal for a synchronization detection signal Ssync.

Claims (1)

[Claim for Utility Model Registration] An automatic channel selection device that is capable of presetting a plurality of broadcast stations to be selected in a memory, which starts a search and selects a channel with a single key operation, and displays the result of the channel selection. is written as the station information of the station in the part of the memory corresponding to one station selection position, and the state after the station selection is maintained until the next key operation. , When a search is started with a single key operation and a broadcast station is selected, the station information is written to the above memory and the search is started again, and the next broadcast station is captured and selected to be stored in the above memory. A second preset mode in which the station operation is repeated, making it possible to select between the two preset modes, and when the second preset mode is selected, the gain of the tuner is lowered and the tuning is adjusted. An automatic channel selection device characterized by being provided with means for reducing signal detection sensitivity.