JPH09130285A - Input circuit for television tuner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drastically reduce the loss of UHF band signals, to perform miniaturization by simple circuit constitution and to lower a manufacture cost. SOLUTION: This circuit is connected between an antenna input terminal 1 to which VHF band and UHF band signals are inputted in common and the input terminal 13 of a television tuner 12 and provided with a first inductor 3 connected between the input terminal 1 and a reference potential point, the serial connection circuit of a capacitor 4 parallelly connected to the inductor 3 and a second inductor 5 and a switching diode 6 parallelly connected to the capacitor 4. The diode 6 is made non-conductive in selecting the VHF band signals and made conductive in selecting the UHF band signals. The inductor 3 provides high impedance to the VHF band signals, a parallel connection circuit composed of the inductors 3 and 5 provides a low impedance to the VHF signals and provides the high impedance to the UHF band signals when the diode 6 is conductive and the serial connection circuit provides extremely low impedance to the UHF band signals when the diode 6 is non-conductive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input circuit of a television tuner, and more particularly, when the VHF band signal and the UHF band signal supplied to an antenna input terminal are combined and transmitted to an input end of the television tuner. In addition, the present invention relates to an input circuit of a television tuner which employs an input circuit having a low loss and a simple circuit configuration.

[0002]

2. Description of the Related Art Conventionally, a VHF band signal and a UHF band signal supplied to an input circuit of a television tuner used in an on-vehicle television device or the like, that is, an antenna input terminal are coupled and transmitted to an input end of the tuner. The input circuit of the television tuner has a UHF and VHF separator for separating and transmitting a VHF band signal and a UHF band signal,
A circuit including a broadband amplifier connected to the UHF and VHF separators and selectively amplifying signals in the UHF band has been used.

FIG. 4 is a circuit diagram showing a schematic configuration of an example of an input circuit of such a known television tuner.

As shown in FIG. 4, the input circuit 40 of the television tuner includes an antenna input terminal 41, a DC blocking capacitor 42, an inductor 43, and a first UH.
F, VHF separator 44, wide band amplifier 45,
Second UHF, VHF separator 46 and operating power supply 4
It consists of seven. Also, the television tuner 48
Has an input end 49 and an output end 50.

The antenna input terminal 41 is connected to an antenna (not shown), and is used for VHF band signals and UHF signals.
The band signal is commonly input. DC blocking capacitor 42
Has one end connected to the antenna input terminal 41 and the other end connected to the reference potential point (ground point) via the inductor 43. The first UHF / VHF separator 44 has a common input end connected to the other end of the DC blocking capacitor 42, and
The output end (the output end of the VHF band signal) is the second UHF, V
The first input end of the HF separator 46 (the input end of the signal in the VHF band) and the second output end (the output end of the signal in the UHF band)
Are connected to the input terminals of the broadband amplifier 45, respectively. The second UHF and VHF separator 46 has a second input end (UHF band signal input end) connected to the output end of the wide band amplifier 45, and a common output end connected to the input end 49 of the next television tuner 48. To be done. The operating power supply 47 is connected to the power supply terminal of the wide band amplifier 45.

The input circuit 40 of the television tuner configured as described above operates as follows.

When the VHF band signal and the UHF band signal received by the antenna are supplied to the antenna input terminal 41 through the coaxial transmission cable (not shown), the VHF band signal and the UHF band signal become a DC blocking capacitor. 42 and the inductor 43 receive almost no signal loss, and are input to the common input terminal of the first UHF / VHF separator 44 via the DC blocking capacitor 42. At this time, the first U
The HF / VHF separator 44 selects a VHF band signal selecting unit having a low-pass filter (LPF) function from the input VHF band signal and UHF band signal in the VHF band signal selecting unit.
The HF band signal is extracted, and the extracted VHF band signal is first
In addition to supplying to the output end, a high-pass filter (HP
F) The UHF band signal selecting section having the function extracts the UHF band signal and supplies the extracted UHF band signal to the second output end. The wideband amplifier 45 amplifies the signal in the UHF band obtained at the second output end and supplies the amplified signal to the first input end of the second UHF / VHF separator 46. In this case, the gain of the broadband amplifier 45 compensates for the loss due to the stray capacitance Ci of the coaxial transmission cable connected to the antenna input terminal 41 and the transmission loss at the first and second UHF and VHF separators 44 and 46. , UHF band signal reception performance is not impaired. The second UHF / VHF separator 46 transmits the VHF band signal supplied to the first input terminal to the VHF band signal selection unit having a low pass filter (LPF) function, and then combines it with the UHF band signal. To the common output end,
In addition, the UHF band signal supplied to the second input terminal is transmitted to the UHF band signal selecting section having a high-pass filter (HPF) function, and then combined with the VHF band signal as described above to be connected to the common output terminal. Supply to. Then the second UHF, V
The VHF band signal and the UHF band signal obtained at the common output end of the HF separator 46 are the television tuner 4
The signal is supplied to the input terminal of 8, and the required channel selection operation is performed there.

FIG. 5 is a characteristic diagram showing an example of frequency transmission characteristics in the input circuit 40 of a known television tuner.

As shown in FIG. 5, wideband amplifier 45
UHF band signals are amplified using
Although the deterioration of the frequency transmission characteristic for the F band signal is compensated, the frequency transmission characteristic is slightly lower than the frequency transmission characteristic for the VHF band signal.

[0010]

In the input circuit 40 of the known television tuner, the stray capacitance Ci of the coaxial transmission cable connected to the antenna input terminal 41 is relatively large (about 3 pF). Since the transmission loss of the UHF band signal selection unit in the second UHF and VHF separators 44 and 46 is relatively large, the loss of the UHF band signal becomes large, and it is difficult to improve the reception performance for the UHF band signal. is there.

However, such a problem is caused by the first UHF,
If a wide band amplifier 45 is connected between the VHF separator 44 and the second UHF / VHF separator 46 and a signal in the UHF band is amplified by the wide band amplifier 45, the problem can be solved to some extent. Since the loss and the transmission loss in the UHF band signal selection unit are large, it is not possible to compensate all of these losses only by amplifying the wide band amplifier 45, and there is still a problem.

Further, since the input circuit 40 of the known television tuner uses the first and second UHF and VHF separators 44 and 46, it is necessary to secure a space for disposing them. Not only the input circuit 40 of becomes large as a whole,
In addition to the necessity of the wide band amplifier 45, there is also a problem that the manufacturing cost of the input circuit 40 of the television tuner becomes high.

The present invention solves these problems, and its purpose is to significantly reduce the loss of signals in the UHF band, to enable downsizing with a simple circuit configuration, and to reduce the manufacturing cost. It is to provide an input circuit of a television tuner.

[0014]

In order to achieve the above object, the present invention provides a connection between an antenna input terminal to which a VHF band signal and a UHF band signal are commonly input and an input end of a television tuner. A first inductor connected between the antenna input terminal and a reference potential point, a capacitor connected in parallel to the first inductor, and a second inductor.
A series connection circuit of inductors and a switching diode connected in parallel to the capacitor, the switching diode being set to a non-conducting state when selecting the VHF band signal, and selecting the UHF band signal. It is provided with a first means which is sometimes set in a conducting state.

In the first means, VH
When the F band signal is selected, the switching diode is set to the non-conducting state, and the first inductor and the series connection circuit of the capacitor and the second inductor are inserted and connected to the input circuit of the television tuner, The impedance of the parallel connection circuit including the inductor and the series connection circuit is configured to be high for VHF band signals and low for UHF band signals.
The signal in the F band is transmitted in the input circuit of the television tuner in a low loss state, whereas the signal in the UHF band suffers a large loss in the input circuit of the television tuner and is not substantially transmitted. On the other hand, when selecting the UHF band signal,
The switching diode is set to the conductive state, the first inductor and the second inductor are inserted and connected to the input circuit of the television tuner, and the impedance of the parallel connection circuit including the first inductor and the second inductor is set to V
Since it is configured to be low for signals in the HF band and high for signals in the UHF band, signals in the VHF band are not transmitted due to a large loss in the input circuit of the television tuner. On the other hand, UHF band signals are transmitted in a low loss state in the input circuit of the television tuner.

In order to achieve the above object, the present invention is connected between an antenna input terminal to which a VHF band signal and a UHF band signal are commonly input, and an input end of a television tuner, A first switching diode connected in series between an input terminal and the input end of the television tuner, and a series connection via a buffer circuit between the antenna input terminal and the input end of the television tuner. A second switching diode, a first inductor connected between the antenna input terminal and a reference potential terminal, a capacitor connected in parallel with the second switching diode, the second switching diode and a buffer A second inductor connected between a connection point of the circuit and a reference potential end, the first switch The diode is set to a conductive state when selecting the VHF band signal, and set to a non-conductive state when selecting the UHF band signal, and the second switching diode is set to a non-conductive state when selecting the VHF band signal. And a second means that is set to a conductive state when the signal in the UHF band is selected.

In the second means, VH
At the time of selecting the F-band signal, the first switching diode is set to the conducting state and the second switching diode is set to the non-conducting state, and the first inductor and the series connection circuit of the capacitor and the second inductor are connected. Is inserted and connected to the input circuit of the television tuner, and the impedance of the parallel connection circuit including the first inductor and the series connection circuit is high for a signal in the VHF band and UH
Since it is configured to be lower than the F band signal, the VHF band signal is transmitted in the input circuit of the television tuner in a low loss state via the first switching diode in the conductive state. In contrast, the UHF band signal suffers a large loss in the input circuit of the television tuner and is not substantially transmitted. On the other hand, when selecting a signal in the UHF band, the first switching diode is set to the non-conducting state and the second switching diode is set to the conducting state so that the first inductor and the second inductor are input to the television tuner. The impedance of the parallel connection circuit, which is connected to the circuit by the first inductor and the second inductor, is low with respect to the VHF band signal, and U
Since it is configured to be higher than the signal in the HF band, the signal in the VHF band receives a large loss in the input circuit of the television tuner due to the first switching diode in the non-conduction state. While not transmitted at all, signals in the UHF band are transmitted in the input circuit of the television tuner in a low loss state via the buffer circuit.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit configuration diagram showing a first embodiment of an input circuit of a television tuner according to the present invention.

As shown in FIG. 1, the input circuit 20 of the television tuner includes an antenna input terminal 1, a first DC blocking capacitor 2, a first inductor 3, a capacitor 4, and a second inductor. 5, a switching diode 6, a second DC blocking capacitor 7, a first bias resistor 8, a second bias resistor 9, a bias power supply 10, and a switch 11. The television tuner 12 also has an input end 13 and an output end 14.

The antenna input terminal 1 is connected to an antenna (not shown), and a VHF band signal and a UHF band signal are commonly input. First DC blocking capacitor 2
Has one end connected to the antenna input terminal 1 and the other end connected to the first
Is connected to the reference potential point (ground point) via the inductor 3 and is connected to the coupling point A. Capacitor 4
Has one end connected to the coupling point A and the other end connected to one end of the second inductor 5. The other end of the second inductor 5 is connected to the reference potential point via the second DC blocking capacitor 7. The switching diode 6 has a cathode connected to the coupling point A and an anode connected to the other end of the capacitor 4. The first bias resistor 8 has one end connected to the other end of the second inductor 5 and the other end connected to the reference potential point via the second bias resistor 9. Switch 11
It has two fixed contacts u and v and one movable contact s, and one fixed contact u is connected to the other end of the first bias resistor 8 and the other fixed contact v is open-connected and the movable contact s is Is connected to the reference potential point via the bias power supply 10. Further, the connection point A is connected to the input terminal 13 of the television tuner 12 that follows.

In this case, the first inductor 3 has a VHF
When the inductance value is selected so as to exhibit a high impedance with respect to the band signal, and the switching diode 6 is in the conductive state, the parallel connection circuit including the first inductor 3 and the second inductor 5 has a VHF band. Their inductance values are selected to present a low impedance for the signal and a high impedance for the UHF band signal. Furthermore, when the switching diode 6 is in the non-conducting state, the series connection circuit of the capacitor 4 and the second inductor 5 exhibits an extremely low impedance with respect to a signal in the UHF band, that is,
The capacitance value of the capacitor 4 and the inductance value of the second inductor 5 are selected so as to be in a substantially resonant state.

The input circuit 20 of the television tuner configured as described above operates as follows.

First, the VH on the television tuner 12
When the F band signal is selected, the movable contact s of the switch 11 is switched and connected to the other fixed contact v side, and the DC bias voltage is not supplied to the switching diode 6, so that the switching diode 6 becomes non-conductive. In this state, the first inductor 3 and the series connection circuit of the capacitor 4 and the second inductor 5 are connected in parallel between the connection point A and the reference potential point (ground point). In addition,
A second DC blocking capacitor 7 is also connected in series to this series connection circuit, but the second DC blocking capacitor 7 is V
Since the impedance of the HF band signal (and also the UHF band signal) is almost zero, the result is the same even if the connection of the second DC blocking capacitor 7 is ignored.

Here, when the VHF band signal and the UHF band signal received by the antenna are supplied to the antenna input terminal 1 through the coaxial transmission cable (not shown), VH band signal
The F band signal and the UHF band signal are transmitted through the DC blocking capacitor 2 with almost no loss and supplied to the coupling point A. At this time, the first inductor 3 connected between the coupling point A and the reference potential point exhibits a high impedance with respect to the VHF band signal and the UHF band signal, and thus the VHF band signal and the UHF band signal. Signal is not bypassed through the first inductor 3. Further, the series connection circuit of the capacitor 4 and the second inductor 5, which is also connected between the coupling point A and the reference potential point, exhibits a relatively high impedance with respect to the signal in the VHF band, and therefore, in the VHF band. Although the signal is not bypassed through this series circuit, it presents a very low impedance to signals in the UHF band, so UH
Most of the signals in the F band are bypassed through this series connection circuit. As a result, VH supplied to the connection point A
Among the F band signal and the UHF band signal, the VHF band signal is hardly attenuated, while the UHF band signal is almost attenuated and only the VHF band signal is selected. Is supplied to the input terminal 13 of the television tuner 12.

On the other hand, the UHF on the television tuner 12
When selecting the band signal, the movable contact s of the switch 11
Is switched and connected to one fixed contact u side, the DC bias voltage of the bias power supply 10 is supplied to the switching diode 6, and the switching diode 6 becomes conductive. In this state, the capacitor 4 is short-circuited by the switching diode 6 in the conductive state, so that the connection point A
The first inductor 3 and the second inductor 5 are connected in parallel between and and the reference potential point (ground point).

When the VHF band signal and the UHF band signal received by the antenna are supplied to the antenna input terminal 1 through the coaxial transmission cable, the VHF band signal and the UHF band signal are fed to the DC blocking capacitor 2. Are transmitted with almost no loss and are supplied to the connection point A. At this time, the connection point A
The parallel connection circuit of the first inductor 3 and the second inductor 5 connected between the reference potential point and the reference potential point exhibits a low impedance with respect to the VHF band signal, and therefore most of the VHF band signal is Although it is bypassed through this parallel connection circuit, the UHF band signal is not bypassed through this parallel connection circuit because it presents a high impedance to the UHF band signal. As a result, of the VHF band signal and the UHF band signal supplied to the connection point A, the VHF band signal is almost attenuated, while the UHF band signal is hardly attenuated. Only signals in the UHF band are selected and supplied to the input terminal 13 of the next television tuner 12.

After the VHF band signal or the UHF band signal is supplied to the television tuner 12, the television tuner 12 selects the required receiving channel as in the normal operation.

FIG. 3 is a characteristic diagram showing frequency transmission characteristics of the input circuit 20 of the television tuner according to the first embodiment.

As shown in FIG. 3, the input circuit 20 of the television tuner according to the first embodiment uses a wide band amplifier like the input circuit of a known television tuner to deteriorate the frequency transmission characteristic. The frequency transmission characteristic for the UHF band signal is significantly improved even without the compensation of the UHF band.
Both the frequency transmission characteristics for the F band signal are good.

As described above, according to the first embodiment of the present invention, like the input circuit 40 of the known television tuner, the UHF and VH that cause a relatively large transmission loss.
Since the F separators 44 and 46 are not used, the loss of signals in the UHF band can be significantly reduced, and
Since the UHF and VHF separators 44 and 46 and the wide band amplifier 45 are not used, the circuit configuration is simplified, the size can be reduced, and the manufacturing cost can be reduced.

Next, FIG. 2 is a circuit configuration diagram showing a second embodiment of the input circuit of the television tuner according to the present invention.

As shown in FIG. 2, the input circuit 30 of the television tuner includes an antenna input terminal 1, a first DC blocking capacitor 2, a first inductor 3, a capacitor 4, and a second inductor. 5, a second DC blocking capacitor 7, a first bias resistor 8, a second bias resistor 9, a bias power supply 10, a switch 11, a first switching diode 15, and a second switching diode. 16, the third bias resistor 17, the fourth
Bias resistor 18 and wide band amplifier 19. In addition, the television tuner 12 has an input terminal 13
And an output end 14.

The antenna input terminal 1 is connected to an antenna (not shown), and a VHF band signal and a UHF band signal are commonly input. First DC blocking capacitor 2
Has one end connected to the antenna input terminal 1 and the other end connected to the first
Is connected to the reference potential point (ground point) via the inductor 3 and is connected to the coupling point A. Capacitor 4
Has one end connected to the connection point A and the other end connected to the connection point B. The second inductor 5 has one end connected to the coupling point B and the other end connected to the reference potential point via the second DC blocking capacitor 7. First switching diode 1
5, the cathode is connected to the connection point A and the anode is connected to the connection point C. One end of the first bias resistor 8 is connected to the coupling point B, and the other end is connected to the reference potential point via the second bias resistor 9. The second switching diode 16 has a cathode connected to the coupling point A and an anode connected to the coupling point B. The third bias resistor 17 is
One end is connected to the connection point C, and the other end is connected to the reference potential point via the fourth bias resistor 18. Switch 11
Has two fixed contacts u and v and one movable contact s, one fixed contact u is connected to the other end of the first bias resistor 8, and the other fixed contact v is the third bias. Resistance 1
7, the movable contact s is connected to the reference potential point via the bias power source 10. The broadband amplifier 19 is
The input end is connected to the coupling point B, the output end is connected to the coupling point C, and the power supply terminal is connected to the bias power supply 10. Further, the connection point C is connected to the input terminal 13 of the television tuner 12 that follows.

In this case, the first inductor 3 has a VHF
When the inductance value is selected so as to exhibit a high impedance with respect to the signal of the band, the first switching diode 15 is in a non-conducting state, and the second switching diode 16 is in a conducting state, the first inductor 3 and The parallel connection circuit composed of the second inductor 5 exhibits low impedance for signals in the VHF band, and
Their inductance values are selected so that they exhibit a high impedance for signals in the HF band. further,
When the first switching diode 15 is in the conducting state,
When the switching diode 16 of is in a non-conducting state, the series connection circuit of the capacitor 4 and the second inductor 5 is
Capacitor 4 has an extremely low impedance with respect to the UHF band frequency, that is, a substantially resonant state.
And the inductance value of the second inductor 5 are selected.

The input circuit 30 of the television tuner configured as described above operates as follows.

First, VHF is displayed on the television tuner 12.
When selecting the band signal, the movable contact s of the switch 11
Is switched and connected to the other fixed contact v side, the DC bias voltage of the bias power supply 10 is supplied to the first switching diode 15, the first switching diode 15 is turned on, and the DC bias is applied to the second switching diode 16. The second switching diode 16 is brought into a non-conducting state by supplying no voltage. In this state, the first inductor 3 and the series connection circuit of the capacitor 4 and the second inductor 5 are connected in parallel between the coupling point A and the reference potential point (ground point). Although the second DC blocking capacitor 7 is connected in series to this series connection circuit, the second DC blocking capacitor 7 is almost zero for VHF band signals (also for UHF band signals). Since it is impedance, the result is the same even if the connection of the second DC blocking capacitor 7 is ignored.

Here, when the VHF band signal and the UHF band signal received by the antenna are supplied to the antenna input terminal 1 through the coaxial transmission cable (not shown), VH band signal
The F band signal and the UHF band signal are transmitted through the DC blocking capacitor 2 with almost no loss and supplied to the coupling point A. At this time, the first inductor 3 connected between the coupling point A and the reference potential point exhibits a high impedance with respect to the VHF band signal and the UHF band signal, and thus the VHF band signal and the UHF band signal. Signal is not bypassed through the first inductor 3. Further, the series connection circuit of the capacitor 4 and the second inductor 5, which is also connected between the coupling point A and the reference potential point, exhibits a relatively high impedance with respect to the signal in the VHF band, and therefore, in the VHF band. Although the signal is not bypassed through this series circuit, it presents a very low impedance to signals in the UHF band, so UH
Most of the signals in the F band are bypassed through this series connection circuit. As a result, VH supplied to the connection point A
Among the F band signal and the UHF band signal, the VHF band signal is hardly attenuated, while the UHF band signal is largely attenuated, so that only the VHF band signal is selectively turned on. Is supplied to the connection point C through the first switching diode 15 at the same time, and at the same time, is supplied to the input terminal 13 of the next television tuner 12. In this state, since the power supply voltage is not supplied to the wide band amplifier 19, the wide band amplifier 19 does not perform a normal amplification operation.

On the other hand, the UHF on the television tuner 12
When selecting the band signal, the movable contact s of the switch 11
Is connected to one fixed contact u side by switching, and the DC bias voltage is not supplied to the first switching diode 15,
Make the first switching diode 15 non-conductive,
The bias power supply 10 is connected to the second switching diode 16.
The DC bias voltage is supplied to bring the second switching diode 16 into conduction. In this state,
Since the capacitor 4 is short-circuited by the second switching diode 16 in the conductive state, the first inductor 3 and the second inductor 5 are connected in parallel between the coupling point A and the reference potential point (ground point). To be done.

When the VHF band signal and the UHF band signal received by the antenna are supplied to the antenna input terminal 1 through the coaxial transmission cable, the VHF band signal and the UHF band signal are fed to the DC blocking capacitor 2. Are transmitted with almost no loss and are supplied to the connection point A. At this time, the connection point A
The parallel connection circuit of the first inductor 3 and the second inductor 5 connected between the reference potential point and the reference potential point exhibits a low impedance with respect to the VHF band signal, and therefore most of the VHF band signal is Although it is bypassed through this parallel connection circuit, the UHF band signal is not bypassed through this parallel connection circuit because it presents a high impedance to the UHF band signal. As a result, of the VHF band signal and the UHF band signal supplied to the coupling point A, the VHF band signal is almost attenuated, while the UHF band signal is not largely attenuated. Since it is transmitted to B, only the UHF band signal is selectively supplied to the wide band amplifier 19. Then
The signal in the UHF band is appropriately amplified by the wide band amplifier 19 having a buffer function, and then supplied to the connection point C and, at the same time, supplied to the input terminal 13 of the next television tuner 12.

After the VHF band signal or the UHF band signal is supplied to the television tuner 12, the television tuner 12 selects the required receiving channel as in the normal operation.

Also in the input circuit 30 of the television tuner according to the second embodiment, like the input circuit 20 of the television tuner according to the first embodiment already described, as shown in FIG. Good frequency transmission characteristics can be obtained.

As described above, according to the second embodiment of the present invention, similarly to the above-described first embodiment, as in the input circuit 40 of the known television tuner, a relatively large transmission loss is generated. U, which has a large structure and is relatively expensive
Since HF and VHF separators 44 and 46 are not used,
The loss of signals in the UHF band can be significantly reduced, the circuit configuration can be simplified, the size can be reduced, and the manufacturing cost can be reduced.

In the second embodiment,
An example in which the wide band amplifier 19 is used as a buffer circuit that electrically isolates the coupling point B and the coupling point C when the first switching diode 15 is in the non-conduction state has been described. The buffer circuit is not limited to the wide band amplifier 19, and another buffer circuit may be used as long as it can transmit signals in the UHF band without loss.

[0045]

As described above in detail, according to the present invention, the UHF used in the input circuit of the known television tuner causes a relatively large transmission loss, has a large structure, and is relatively expensive. , The input circuit of the television tuner is configured without using the VHF separator, so the UHF generated by the UHF and VHF separators
There is an effect that the signal loss in the band can be significantly reduced, and since the UHF and VHF separators are not used, the configuration of the input circuit of the television tuner is simplified and the overall size is reduced. Moreover, there is an effect that the manufacturing cost of the input circuit of the television tuner can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of an input circuit of a television tuner according to the present invention.

FIG. 2 is a circuit configuration diagram showing a second embodiment of an input circuit of a television tuner according to the present invention.

FIG. 3 is a characteristic diagram showing an example of frequency transmission characteristics of the input circuit of the television tuner according to the first embodiment shown in FIG.

FIG. 4 is a circuit configuration diagram showing an example of an input circuit of a known television tuner.

FIG. 5 is a characteristic diagram showing an example of frequency transmission characteristics of the input circuit of the known television tuner shown in FIG.

[Explanation of symbols]

 1 Antenna Input Terminal 2 First DC Blocking Capacitor 3 First Inductor 4 Capacitor 5 Second Inductor 6 Switching Diode 7 Second DC Blocking Capacitor 8 First Bias Resistor 9 Second Bias Resistor 10 Bias Power Supply 11 Switch 12 Television Tuner 13 Input Terminal 14 Output Terminal 15 First Switching Diode 16 Second Switching Diode 17 Third Bias Resistor 18 Fourth Bias Resistor 19 Wideband Amplifier 20, 30 Television Tuner Input Circuit

Claims (6)

[Claims] 1. A VHF band signal and a UHF band signal are commonly connected between an antenna input terminal and an input end of a television tuner, and are connected between the antenna input terminal and a reference potential point. A first inductor, a capacitor connected in parallel with the first inductor, and a second inductor
A series connection circuit of inductors and a switching diode connected in parallel to the capacitor, the switching diode being set to a non-conducting state when selecting the VHF band signal, and selecting the UHF band signal. An input circuit of a television tuner, which is sometimes set to a conductive state. 2. The first inductor has a high impedance with respect to a signal in the VHF band, and a parallel connection circuit including the first inductor and the second inductor has a switching diode in a conductive state. When
The VHF band signal has a low impedance, the UHF band signal has a high impedance, and the capacitor and the second inductor are connected in series when the switching diode is in a non-conducting state. The inductance value of each of the first inductor and the second inductor and the capacitance value of the capacitor are selected so as to exhibit an extremely low impedance with respect to the signal in the UHF band. Input circuit of the described television tuner. 3. A VHF band signal and a UHF band signal are commonly input between an antenna input terminal and an input end of a television tuner, and the antenna input terminal and the input end of the television tuner are connected to each other. A first switching diode connected in series between them, a second switching diode connected in series via a buffer circuit between the antenna input terminal and the input end of the television tuner, and the antenna input terminal A first inductor connected between a reference potential terminal, a capacitor connected in parallel with the second switching diode, a connection point between the second switching diode and the buffer circuit, and the reference potential terminal. A second inductor connected thereto, wherein the first switching diode is connected to the VH
The FHF band signal is set to a conductive state when selected, and the UHF band signal is set to a non-conductive state when selected, and the second switching diode is set to a non-conductive state when the VHF band signal is selected and set to the UHF band. An input circuit of a television tuner, which is set to a conductive state when a band signal is selected. 4. The first inductor exhibits a high impedance with respect to a signal in the VHF band, and a parallel connection circuit composed of the first inductor and the second inductor has the second switching diode. When in a conducting state, it exhibits a low impedance with respect to the signal in the VHF band and a high impedance with respect to the signal in the UHF band, and the series connection circuit of the capacitor and the second inductor is the second connection circuit. When the switching diode is in the non-conducting state, the first diode is configured to have an extremely low impedance with respect to the frequency of the UHF band.
4. The input circuit of the television tuner according to claim 3, wherein the inductance values of the inductor and the second inductor, and the capacitance value of the capacitor are respectively selected. 5. The high-frequency amplifier, wherein the buffer circuit is set to a non-operating state when selecting the VHF band signal and an operating state when selecting the UHF band signal, and amplifies the UHF band signal. 4. The method according to claim 3,
The input circuit of the television tuner according to any one of claims 1 to 4. 6. The input circuit of a television tuner according to claim 5, wherein the operating voltage of the high frequency amplifier is shared with a control voltage for setting the second switching diode in a conductive state.