JPH0614607B2 - 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. In a booster for a television receiver in which a path and a through path that does not amplify a signal are provided, and only one of the amplification path and the through path is switched to an operating state by switching means, the television tuner The AGC voltage attenuation adjusting means for greatly attenuating the reverse type AGC voltage output from the VIF circuit in the operating state of the through path and the small attenuation in the operating state of the amplifying path, and the attenuated AGC voltage and the reference voltage are provided. A comparison switching means for switching and controlling the switching means for comparison is provided, and the operation state of the amplification path is In the state, when the AGC voltage 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 which is higher than the first switching voltage. In this case, the switching means is switched to the amplification path, and further, the impedance variable means provided between the signal of the amplification path and the ground, and the AGC voltage of the first and second AGC voltages in the operating state of the amplification path. First gain adjusting means for reducing the impedance of the impedance varying means when the voltage becomes equal to or lower than the third switching voltage set during the switching voltage, and predetermined when the operating state is switched from the through path to the amplification path. And a second gain adjusting means for reducing the impedance of the impedance varying means for a time period. Gain of the amplification path is configured to decrease when the AGC voltage is switched into and the amplification path when the following third switching voltage work state.

(Operation) AGC voltage attenuation adjusting means for greatly attenuating the AGC voltage in the operating state of the through path and small attenuation in the operating state of the amplifying path, and the attenuated AGC voltage and the reference voltage are compared to control switching of the switching means. 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, the switching means is switched to the through path to operate the through path. In this state, the switching means is switched to the amplifying path when the AGC voltage becomes equal to or higher than the second switching voltage which is higher than the first switching voltage. By setting the first and second switching voltages according to the above, the switching from the amplification path to the operating state of the through path and the through It is possible to automatically switch between the path and the operating state of the amplification path with substantially the same electric field strength of the television broadcast radio wave. 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 amplification path, the impedance of the impedance varying means is reduced by the first gain adjusting means. Since the gain of the amplifying path is reduced by changing the AGC voltage to the through path, the electric field strength of the television broadcast radio wave is sufficiently strong, and changes when the operating state of the through path is switched. The AGC voltage to be applied does not exceed the second switching voltage, and the amplification path can be stably switched to the through path operation state. Further, when the AGC voltage rises and switches to the amplification path in the operating state of the through path, the impedance of the impedance changing means is immediately reduced by the second gain adjusting means, so that the operation of the first gain adjusting means is temporarily stopped. Even if it is delayed, the gain of the amplification path can be surely reduced, the AGC voltage does not fall below the first switching voltage, and the through state can be stably switched to the operation 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
A reverse AGC voltage is applied to.

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 through the PNP transistor 13 of the power supply terminal 12 through one of the PNP transistors 13 and becomes 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 TV tuner / VIF circuit 3 to AG
The AGC voltage input terminal 15 to which the C 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 the resistor 18, and is also grounded in parallel with the resistor 19 and the NPN transistor 20 in series. The reference voltage 21 is applied to the other input terminal of the comparator 17. Note that the comparator 17 may have a structure having a built-in reference voltage,
At this time, the reference voltage 21 is unnecessary. And the comparator 17
The output terminal of is connected to the base of one PNP transistor 13 via an inverter 22 and a resistor 23 in series, and is connected to the base of the other PNP transistor 14 via a 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. 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 and the PNP transistor via the capacitor 36.
Connected to 30 emitters. Further, an NPN transistor is provided between the base of the PNP transistor 30 and the ground.
37 is interposed, the base of which is grounded by a resistor 38 and is connected to the connection point of two capacitors 39 and 40 which are interposed in series between the emitter of the PNP transistor 30 and the ground. The comparator 17 and the reference voltage 21 constitute a comparison switching means, and the resistors 16, 18, 19 and the NPN transistor 20 form an AG.
C voltage attenuation adjusting means is configured. Further, the pin diode 27 constitutes an impedance variable means,
The transistor 30, the resistors 31 and 32, the Zener diode 33, and the like constitute a first gain adjusting means, and the PNP transistor 30, the NPN transistor 37, and the capacitors 39 and 40.
The second gain adjusting means is configured by the above.

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 input terminal 15 is supplied with the AGC voltage of 3 V which is the first switching voltage, 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 7.5 V which is the second switching voltage is applied to the AGC voltage input terminal 15, the comparator 17 attenuates 1.25 V 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 non-operational. . 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, when the amplification path 6 is switched to the operating state, the antenna input is greatly amplified, and the AGC voltage output from the television tuner / VIF circuit 3 tends to be 3 V or less of the first switching voltage, but switching is performed. At the same time, the NPN transistor 37 becomes conductive, the PNP transistor 30 becomes conductive, and a forward current flows through the pin diode 27, the gain of the amplification path 6 decreases, and the AGC voltage becomes the third value.
The voltage becomes an intermediate voltage between the first and third switching voltages shown by point b in the figure. The conduction time of the NPN transistor 37 continues for a predetermined time set by the capacitor 40 and the resistor 38, during which the cathode potential of the Zener diode 33 is PNP.
It is lowered until the transistor 30 is turned on, and the gain of the amplifying path 6 is kept lowered. Further, when the electric field strength of the television broadcast radio wave is weakened, the AGC voltage rises up to 3.5V at point c in FIG. 3 along the AGC voltage characteristic of the operating state of the amplification path 6 in which the gain is lowered. 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 AGC voltage becomes 3.5.
A in the operating state of the amplification path 6 in which the gain is not reduced as V
The point d in FIG. 3 on the GC voltage characteristic is reached, and thereafter, the AGC voltage rises along the AGC voltage characteristic in the operating state of the amplification path 6. Thus, even if the amplification degree of the amplification path 6 is large, the operation state of the amplification path 6 after switching can be stably maintained.

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 the second switching due to 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. Here, the capacitor 36 is connected to the input end of the buffer amplifier 34.
The change in the voltage at the output terminal is delayed with respect to the change in the AGC voltage because of the connection of the P.P. Then, in order to compensate for this delay, the NPN transistor 37 immediately becomes conductive when the operating state of the through path 7 is switched to the amplifying path 6, and the PNP transistor 37 is turned on.
The transistor 30 is conducting.

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. Also, AG
The C voltage attenuation adjusting means may have any structure that increases the attenuation amount of the AGC voltage when the through path 7 is in the operating state. Further, it goes without saying that the impedance variable means for adjusting the gain of the amplification path 6 is not limited to the pin diode 27 and may be configured by using an impedance variable element such as a transistor.

(Effects of the Invention) As described above, according to the booster for a television receiver of the present invention, the AGC voltage attenuation adjustment is performed in which the AGC voltage is greatly attenuated in the operating state of the through path and is attenuated slightly in the operating state of the amplifying path. Means and comparison switching means for switching the switching means by comparing the attenuated AGC voltage with the reference voltage, and the AGC output from the television tuner / VIF circuit in the operating state of the amplification path.
The switching means is switched to the through path when the voltage becomes equal to or lower than the first switching voltage, and when the AGC voltage becomes equal to or higher than the second switching voltage which is higher than the first switching voltage in the operating state of the through path. Since A is switched to the amplification path, A
By setting the first and second switching voltages substantially corresponding to the difference in the GC voltage, switching from the amplifying path to the operating state of the through path and switching from the through path to the operating state of the amplifying path are performed. It is possible to switch automatically with almost the same electric field strength of television 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 amplification path, the first
The gain adjusting means reduces the impedance of the impedance varying means to reduce the gain of the amplification path.
When the GC voltage is lowered and switched to the through path, the electric field strength of the television broadcast radio wave is sufficiently strong, and changes when the operating state of the through path is changed.
Since the voltage does not exceed the second switching voltage, it is possible to stably switch from the amplifying path to the operating state of the through path.
Further, when the AGC voltage rises and switches to the amplification path in the operating state of the through path, the impedance of the impedance changing means is immediately reduced by the second gain adjusting means, so that the operation of the first gain adjusting means is temporarily stopped. Even if it is delayed, the gain of the amplification path can be surely reduced, the AGC voltage does not fall below the first switching voltage, and the through state can be stably switched to the operation state of the amplification path. 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, 38: Resistor, 17: Comparator, 20, 37: NPN transistor, 27: Pin diode , 33: Zener diode, 39, 40: Capacitor.

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, an AGC voltage attenuation adjustment in which a reverse type AGC voltage output from the television tuner / VIF circuit is largely attenuated in an operating state of the through path and slightly attenuated in an operating state of the amplification path. Means and comparison switching means for comparing and controlling the switching means by comparing the attenuated AGC voltage with the reference voltage, and when the amplification path is in an operating state, the AGC voltage 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 power is supplied. Second but higher than the first switching voltage
The switching voltage is equal to or higher than the switching voltage, the impedance changing means is provided between the signal of the amplification path and the ground,
First gain adjusting means for reducing the impedance of the impedance varying means when the AGC voltage becomes equal to or lower than a third switching voltage set between the first and second switching voltages in the operating state of the amplification path; Second gain adjusting means for reducing the impedance of the impedance varying means for a predetermined time when the operating state is switched from the through path to the amplifying path, and the AGC voltage is set to the above-mentioned AGC voltage in the operating state of the amplifying path. A booster for a television receiver, wherein the gain of the amplification path is reduced when the voltage is equal to or lower than a third switching voltage or when the amplification path is switched.