JPH0614606B2 - Booster for TV receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is an amplifier that automatically amplifies a signal according to the strength of the electric field strength of a television broadcast radio wave tuned and selected by a television tuner / VIF circuit. The present invention relates to a booster for a television receiver in which one of a path and a through path that does not amplify a signal is appropriately switched to an operating state.

(Prior Art) A conventional general booster for a television receiver has a weak electric field strength of a television broadcast radio wave in a region such as a mountain area where there is a lot of radio interference or a region far from a television broadcast station. In a weak electric field area, the antenna input is appropriately amplified and input to the television tuner / VIF circuit to improve the reception state of the television receiver. However, in a strong electric field region where the electric field strength of television broadcast radio waves is strong, if the antenna input is amplified more than necessary and input to the television tuner / VIF circuit, intermodulation occurs, and conversely the It is easy to deteriorate the reception condition. Therefore, a booster for a conventional television receiver is provided with an amplification path that amplifies a signal and a through path that does not amplify the signal,
It is constructed so that either one of the amplification path and the through path can be operated by a switching means so as to be in an operating state, and the gain can be switched according to the electric field strength of the television broadcast radio wave selected for tuning. Has been

By the way, in an area where the electric field strengths of the received television broadcast radio waves are about the same, the booster does not once amplify the signal and the signal is not amplified when the television receiver is installed. It suffices to set which of the through paths is in the operating state by manual switching by the switching means, and there is no problem even with the conventional booster for the television receiver described above. However,
In an area where the electric field strength of one television broadcast radio wave received is strong but the electric field strength of another television broadcast radio wave is weak, the reception is performed in order to maintain a good reception state of the television receiver. Each time the channel is switched according to the electric field strength of the television broadcast radio wave, the booster is manually switched by the switching means which of the amplification path that amplifies the signal and the through path that does not amplify the signal is in the operating state. You have to
There is a problem that the effort is complicated.

Therefore, a technique for automatically switching which of an amplification path that amplifies a signal and a through path that does not amplify the signal to be in operation in accordance with the electric field strength of a television broadcast radio wave has been developed. -63117 and Japanese Utility Model Laid-Open No. 58-66719.

To briefly explain the technique disclosed in Japanese Utility Model Laid-Open No. 56-63117, the reference voltage obtained by dividing the drive voltage of the amplification path is compared with the AGC voltage of the forward system, and the AGC voltage is large. Sometimes the electric field strength of the television broadcast radio wave is large, so the through path is conducted,
When the voltage is small, the electric field strength is small, so the amplification path is operated.

Further, to briefly explain the technique disclosed in Japanese Utility Model Laid-Open No. 58-66719, an attenuator is provided in a signal path, a reference voltage and an AGC voltage are compared, and attenuation is performed according to the magnitude of the AGC voltage. Device is activated or deactivated.

(Problems to be Solved by the Invention) The technique disclosed in the above publication is excellent in that the through path and the operation path are automatically switched, but has the following problems.

First, in the technique disclosed in Japanese Utility Model Laid-Open No. 56-63117, if the electric field strength of the television broadcast radio wave becomes large and the AGC voltage slightly exceeds the reference voltage while the amplification path is operating, the amplification is performed. The route is switched to the through route. By this switching, the signal applied to the AGC detection circuit becomes small due to the change in the amplification degree, and the AGC voltage also rapidly decreases. Therefore, the AGC voltage does not reach the reference voltage, and the through path is switched to the amplification path again. Therefore, the through path and the operation path may be switched alternately, and stable and good reception may be hindered by the television receiver.

In the technique disclosed in Japanese Utility Model Laid-Open No. 58-66719, the attenuator is switched from operating to non-operating.
The GC voltage changes abruptly, causing the same problem as the technique of Japanese Utility Model Laid-Open No. 56-63117.

An object of the present invention is to solve the above problems of the conventional booster for a television receiver, and to adjust the electric field strength of the television broadcast radio wave tuned and selected by the television tuner / VIF circuit. To provide a booster for a television receiver capable of automatically switching between an amplification path that amplifies a signal and a through path that does not amplify a signal and maintaining a stable and good reception state. Especially.

(Means for Solving the Problem) In order to achieve such an object, a booster for a television receiver of the present invention is interposed between an antenna and a television tuner / VIF circuit, and an amplifier for amplifying a signal. A booster for a television receiver in which a path and a through path that does not amplify a signal are provided, and one of these amplification path and through path is switched to an operating state by a switching means, and the switching means is controlled. And a gain adjusting means for adjusting the gain of the amplifying path, and the reverse type AGC voltage output from the television tuner / VIF circuit is the first when the amplifying path is operated by the controlling means. When the voltage becomes equal to or lower than the switching voltage, the switching means is switched to the through path and the through path is activated. In the working state, the switching means is switched to the amplification path when the AGC voltage becomes equal to or higher than the second switching voltage which is higher than the first switching voltage, and the gain adjustment means operates the amplification path. At this time, when the AGC voltage becomes equal to or lower than the third switching voltage set between the first and second switching voltages, the gain of the amplification path is reduced.

(Operation) The control means for controlling the switching means is switched to the through path when the AGC voltage output from the television tuner / VIF circuit becomes equal to or lower than the first switching voltage in the operating state of the amplification path, In the operating state of the through path, the switching means is switched to the amplification path when the AGC voltage becomes equal to or higher than the second switching voltage which is higher than the first switching voltage. Therefore, the difference in the AGC voltage depending on the presence or absence of the gain in the amplification path. By setting the first and second switching voltages substantially corresponding to the above, the switching from the amplification path to the operating state of the through path and the switching from the through path to the operating state of the amplification path are almost the same. It can be switched automatically depending on the electric field strength of broadcast radio waves. Moreover, when the AGC voltage becomes equal to or lower than the third switching voltage set between the first and second switching voltages in the operating state of the amplifying path, the gain adjusting means lowers the gain of the amplifying path. Therefore, when the AGC voltage drops and is switched to the through path, the electric field strength of the television broadcast radio wave is sufficiently strong, and the AGC voltage that changes when the operating state of the through path is switched is the second switching voltage. The above does not occur, and the operation state of the through path can be stably switched from the amplification path. Further, when the AGC voltage in the operating state of the through path rises and switches to the amplification path, the AGC voltage tends to become equal to or lower than the first switching voltage, but at the same time as the switching, the gain of the amplification path decreases and the AGC voltage decreases. Does not fall below the first switching voltage, and it is possible to stably switch from the through path to the operating state of the amplification path. Therefore, the amplification degree of the amplification path can be increased. Therefore, it is possible to always maintain a good reception state regardless of the electric field strength of the television broadcast radio wave without the need for manual switching.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a block diagram of a television receiver using a booster for the television receiver of the present invention, and FIG. 2 is a circuit diagram of a booster for the television receiver of the present invention. FIG. 3 is a characteristic diagram of the AGC voltage output from the television tuner / VIF circuit in the operating states of the amplification path and the through path.

In FIG. 1, a booster 1 for a television receiver according to the present invention comprises an antenna 2 and a television tuner / VIF.
It is provided between the antenna input terminal 3a of the circuit 3 and the antenna input of the antenna 2 is amplified or given to the antenna input terminal 3a of the VIF circuit 3 without being amplified. V
AGC voltage input terminal 15 from AGC terminal 3b of IF circuit 3
Is supplied with the AGC voltage.

Hereinafter, the booster 1 for a television receiver of the present invention will be described in detail. In FIG. 2, a multi-stage amplifier is interposed in series between the input terminal 4 and the output terminal 5 to amplify and output the antenna input, and the amplification path 6 and the antenna input are output without being amplified. The through path 7 is provided in parallel. The switching diodes 8 and 9 are reversely connected and interposed between the input terminal 4 and the amplification path 6, and the other switching diodes 10 and 11 are reversely connected between the input terminal 4 and the through path 7. When a forward current flows from the power supply terminal 12 through one PNP transistor 13 to the switching diodes 8 and 9 to make them conductive, the other switching diodes 10 and 11 receive reverse bias and become non-conductive. Conversely, when a forward current flows from the power supply terminal 12 through the other PNP transistor 14 to the other switching diodes 10 and 11 to make them conductive, the switching diodes 8 and 9 receive reverse bias and become non-conductive, and the amplification path Only one of 6 and the through path 7 is configured to be in an operating state. These switching diodes 8, 9, 10, 11 and PNP transistors 13, 14 constitute switching means. Furthermore, from the television tuner / VIF circuit 3 to the AGC
The AGC voltage input terminal 15 to which the voltage is applied is connected to one input terminal of the comparator 17 via the resistor 16. One input terminal of the comparator 17 is grounded via a resistor 18, and in parallel with this, a resistor 19 and an NPN transistor are connected.
Grounded via 20 in series. The reference voltage 21 is applied to the other input terminal of the comparator 17. Note that the comparator
The reference voltage 21 may be unnecessary in this case, as 17 may have a structure having a built-in reference voltage. The output terminal of the comparator 17 is connected to the base of one PNP transistor 13 via the inverter 22 and the resistor 23 in series, and is connected to the base of the other PNP transistor 14 via the resistor 24. . Further, the collector of the other PNP transistor 14 is connected to the base of the NPN transistor 20 via the resistor 25. The base of the NPN transistor 20 is grounded via the resistor 26. Further, a pin diode 27 is connected between the signal line of the amplification path 6 and the ground, and the anode of this pin diode 27 is a choke coil.
It is connected to the collector of a PNP transistor 30 via a resistor 28 and a resistor 29 in series. The emitter of this PNP transistor 30 is connected to the base via a resistor 31, and
It is connected to the collector of one PNP transistor 13. Further, the base of the PNP transistor 30 has a resistor 32.
And Zener diode 33 in series
Connected to 34 outputs. The input terminal of the buffer amplifier 34 is connected to the AGC voltage input terminal 15 via the resistor 35. The comparator 17 and the reference voltage 21 constitute a comparison switching means, and the resistors 16, 18, 19 and the NPN transistor 20 are included.
The attenuation adjusting means is constituted by, and the comparison switching means and the attenuation adjusting means constitute control means for controlling the switching means. Further, the pin diode 27, the PNP transistor 30, the Zener diode 33 and the like constitute a gain adjusting means.

In such a configuration, when the reference voltage 21 is set to 1.25 V, the NPN transistor 20 is non-conductive, and the AGC voltage of 3 V which is the first switching voltage is applied to the AGC voltage input terminal 15, the resistors 16 and 18 are divided. Thus, the resistors 16 and 18 are set so that the comparator 17 is provided with the attenuated AGC voltage of 1.25V. In addition, the NPN transistor 20 becomes conductive and the resistance 19
Is connected in parallel to the resistor 18 and the AGC voltage of 7.5V which is the second switching voltage is applied to the AGC voltage input terminal 15, the comparator 17 attenuates the voltage of 1.25V by the voltage division of the resistors 16, 18 and 19. The resistor 19 is set so that a different AGC voltage is applied.
Furthermore, when the AGC voltage of 3.5 V or less, which is the third switching voltage, is applied to the AGC voltage input terminal 15, the Zener voltages of the resistors 31 and 32 and the Zener diode 33 are set so that the PNP transistor 30 becomes conductive.

Here, first, the electric field strength of the television broadcast radio wave tuned and selected by the television tuner / VIF circuit 3 is extremely strong, and the AGC voltage output from the television tuner / VIF circuit 3 is 3 V or less of the first switching voltage. if there is,
OV is output from the comparator 17 so that the other PNP transistor 14 becomes conductive, and one PNP transistor 13 that is inverted and given by the inverter 22 becomes non-conductive. Therefore, a forward current flows through the other switching diodes 10 and 11 to make them conductive so that the through path 7 is activated, and the switching diodes 8 and 9 are reversely biased to become non-conductive and the amplification path 6 becomes inactive. . The other PN
When the P-transistor 14 is turned on and the through path 7 is activated, the NPN transistor 20 is turned on and the AGC voltage applied to the AGC voltage input terminal 15 is greatly attenuated and applied to the comparator 17.

Next, the electric field strength of the television broadcast radio wave selected for tuning becomes weak while the through path 7 remains in the operating state, and the AGC voltage from the television tuner / VIF circuit 3 becomes the second value shown by point a in FIG. When the switching voltage exceeds 7.5 V, the comparator 17 inverts and outputs 12 V, which is the power supply voltage, to the output terminal. Therefore, this time the other PNP transistor
14 becomes non-conductive, and one PNP transistor 13 which is inverted and given by the inverter 22 becomes conductive. Therefore, a forward current flows through the switching diodes 8 and 9 to make them conductive so that the amplification path 6 is activated, and the other switching diodes 10 and 11 are reversely biased to become non-conductive and the through path 7 becomes inoperative. . The other PN
When the P-transistor 14 becomes non-conductive and the through path 7 becomes inactive, the NPN transistor 20 becomes non-conductive and reduces the amount of attenuation of the AGC voltage applied to the AGC voltage input terminal 15. Here, the antenna input is amplified by the operation of the amplification path 6, and the television tuner
The AGC voltage output from the VIF circuit 3 tends to be 3 V or less of the first switching voltage, but as soon as the AGC voltage becomes 3.5 V or less of the third switching voltage, the PNP transistor is immediately output.
When 30 becomes conductive, a forward current flows through the pin diode 27, the gain of the amplification path 6 is reduced, and the AGC voltage becomes a voltage intermediate between the first and third switching voltages shown at point b in FIG. Furthermore, if the electric field strength of the television broadcast radio wave becomes weak, A
The GC voltage is A in the operating state of the amplification path 6 whose gain has been lowered.
The voltage rises up to 3.5V at point c in FIG. 3 according to the GC voltage characteristic. Further, when the electric field strength of the television broadcast radio wave becomes weaker, the gain of the amplification path 6 gradually increases, and the AG
Amplification path 6 where the C voltage remains at 3.5V and the gain is not reduced
Point d in FIG. 3 on the AGC voltage characteristic of the operating state of A, and thereafter, along the AGC voltage characteristic of the operating state of the amplification path 6, AG
The C voltage rises. In this way, the amplification degree of the amplification path 6 is large and stable, and the operating state of the amplification path 6 after switching can be continued.

On the contrary, when the electric field strength of the television broadcast radio wave tuned and selected in the operating state of the amplification path 6 becomes strong, the third
Amplification path 6 whose gain is reduced from point d to point c in the figure
Point A on the AGC voltage characteristic of the first switching voltage of 3
It becomes V or less. When this AGC voltage becomes 3 V or less, the comparator 17 inverts and outputs 0 V to the output end. Therefore, although the through path 7 is in the operating state and the amplifying path 6 is in the non-operating state, the electric field strength of the television broadcast radio wave is sufficiently strong and the AGC voltage is switched to the second by the AGC voltage characteristic in the operating state of the through path 7. This is point f in FIG. 3 which is slightly lower than the voltage. Further, when the electric field strength of the television broadcast radio wave becomes strong, the AGC voltage decreases along the AGC voltage characteristic in the operating state of the through path 7. In this way, the operating state of the through path 7 after switching can be continued.

Thus, the amplification degree of the amplification path 6 is large (for example, 30
even if it is dB), the switching between the operating states of the through path 7 and the amplifying path 6 can be stably performed, and further, the switching from the amplifying path 6 to the operating state of the through path 7 and the through path 7 Can be switched to the operating state of the amplification path 6 by a slight difference in the electric field strength of the television broadcast radio wave.

In the above embodiment, the switching means is composed of a semiconductor element, but the invention is not limited to this, and a mechanical switch such as a relay may be included. Further, the attenuation adjusting means constituting the control means may be of any configuration that increases the attenuation amount of the AGC voltage when the through path 7 is in the operating state. Further, in place of the attenuation adjusting means, A
An amplifier may be provided between the GC voltage input terminal 15 and the comparator 17 so that its gain becomes small when the through path 7 is in the operating state. Further, the attenuation adjusting means may be omitted from the control means, the reference voltage 21 of the comparator 17 may be switched, and the switching means may be switched by the AGC voltage of the first and second switching voltages. good. The gain adjusting means for adjusting the gain of the amplifying path 6 is not limited to the pin diode 27, and may be configured by using an impedance variable element such as a transistor. Further, the gain adjusting means is the gain of the amplifier itself which constitutes the amplifying path 6. Of course, it may be adjusted.

(Effects of the Invention) As described above, according to the booster for a television receiver of the present invention, the control means for controlling the switching means is provided with the television tuner
When the AGC voltage output from the VIF circuit becomes equal to or lower than the first switching voltage, the switching means is switched to the through path, and in the operating state of the through path, the AGC voltage is equal to or higher than the second switching voltage higher than the first switching voltage. Since the switching means is switched to the amplification path when it becomes, by setting the first and second switching voltages substantially corresponding to the difference in the AGC voltage depending on the presence or absence of gain in the amplification path,
The switching from the amplification path to the operating state of the through path and the switching from the through path to the operating state of the amplification path can be automatically switched with substantially the same electric field strength of the television broadcast radio wave. Moreover, when the amplification path is operating, A
A third voltage whose GC voltage is set between the first and second switching voltages.
Since the gain adjusting means lowers the gain of the amplification path when the voltage becomes equal to or lower than the switching voltage, the electric field strength of the television broadcast radio wave is sufficiently high when the AGC voltage is lowered and the switching to the through path is performed. The AGC voltage that strongly changes when switching to the operating state of the through path does not exceed the second switching voltage, and it is possible to stably switch from the amplifying path to the operating state of the through path. When the AGC voltage in the operating state of the through path rises and switches to the amplification path,
The AGC voltage tries to fall below the first switching voltage, but at the same time as the switching, the gain of the amplification path is reduced and the AGC voltage does not fall below the first switching voltage, and the operating state from the through path to the amplification path is stable. Can be switched to. Therefore, the amplification degree of the amplification path can be increased. Therefore, there is an excellent effect that a good reception state can always be maintained regardless of the electric field strength of the television broadcast radio wave without the need for manual switching.

[Brief description of drawings]

FIG. 1 is a block diagram of a television receiver using a booster for the television receiver of the present invention, and FIG. 2 is a circuit diagram of a booster for the television receiver of the present invention. FIG. 3 is a characteristic diagram of the AGC voltage output from the television tuner / VIF circuit in the operating states of the amplification path and the through path. 1: booster for television receiver, 2: antenna, 3: television tuner / VIF circuit, 4: input terminal, 5: output terminal, 6: amplification path, 7: through path, 8, 9, 10, 11 : Switching diode, 13, 14, 30: PNP transistor, 15: AGC voltage input terminal, 16, 18, 19, 31, 32: Resistor, 17: Comparator, 20: NPN transistor, 27: Pin diode, 33: Zener diode.

Claims (1)

[Claims] 1. An antenna and a television tuner / VIF
An amplification path for amplifying a signal and a through path that does not amplify the signal are provided between the circuit and the amplification path and the through path, and only one of the amplification path and the through path is switched to an operating state by a switching means. In a booster for a television receiver, a control means for controlling the switching means and a gain adjusting means for adjusting the gain of the amplifying path are provided, and the television tuner / VIF in the operating state of the amplifying path by the controlling means. When the reverse AGC voltage output from the circuit becomes equal to or lower than the first switching voltage, the switching means is switched to the through path, and the AGC is in an operating state of the through path.
The switching means is switched to the amplification path when the voltage becomes equal to or higher than a second switching voltage which is higher than the first switching voltage, and further, the AGC is performed when the amplification path is operating by the gain adjusting means. A television receiver, characterized in that the gain of the amplification path is reduced when the voltage becomes equal to or lower than a third switching voltage set between the first and second switching voltages. Booster for machine.