JPH02266604A - High frequency amplifier device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high frequency amplification device for the video field, which is built into, for example, a television receiver or the like.

[Conventional technology]

In recent years, high-frequency amplification devices built into, for example, television receivers are required to have increasingly higher performance as the video field develops.

An example of a conventional high frequency amplification device will be described below with reference to the drawings.

FIG. 3 shows a circuit diagram of an example of a conventional high frequency amplification device.

The high frequency amplification device shown in FIG.
A drain D of a dual gate type field effect transistor 1 for high frequency amplification, whose gate Gl is supplied with an HF input signal, is connected to the VHFt source terminal via a switching element 3 and a choke coil 10 in this order. Further, the drain D of the field effect transistor 2 for high frequency amplification of the dual gate type, in which the UHF input signal is supplied from the signal input terminal B to the gate G1, is connected to the switching element 4, the high frequency coil 14, and the choke coil 11 in this order. Connected to UHFta terminal F.

Furthermore, the switching element 3 and the choke coil lO
connection point, high frequency coil 14 and choke coil 11
A series circuit of a capacitor 12' and a resistor 13' is connected between the connection point of the capacitor 12' and the resistor 13'.

Then, a U I-1F/V HF composite output terminal G' is provided at the connection point between the high frequency coil 14 and the switching element 4, and when the V HF signal is selected, the switching element 3 is made conductive and the switching element 4 is cut off, and the UHF signal is selected. At times, the switching element 4 is made conductive and the switching element 3 is made to be cut off. In this case, the conduction/cutoff of the switching diode, which is the switching element 3.4, is carried out between the y HF z source terminal E and the UH
It is controlled by changing the power supply voltage applied to the FHF power supply terminal.

Specifically, by setting the voltage applied to the VHF power supply terminal E to, for example, +12V and setting the voltage applied to the Ul-IF power supply terminal to, for example, Ov, the switching element 3 is made conductive and the switching element 4 is cut off. let

Also, the voltage applied to the LJHF power supply terminal F is set to +12, for example.
By setting the voltage to V and the voltage applied to the ■1■F power supply terminal E to, for example, OV, the switching element 4 is made conductive and the switching element 3 is cut off. In the above, the voltage III applied to the VHFHF power supply terminal and the UHFHF power supply terminal is set so that when the voltage applied to either one becomes +12V, for example, the other becomes Ov.

Note that Z is an AGC signal input terminal connected to the gate G2 of the field effect transistor 2, and Y is an AGC signal input terminal connected to the gate G2 of the field effect transistor 2.

5 to 8 are resistors, and 9 is a capacitor.

The operation of the high frequency amplification device configured as described above will be explained below.

First, a VHF input signal is applied to signal input terminal C, and U
An HF input signal is applied to signal input terminal B.

First, when selecting a VHF signal, the voltage applied to the VHF power supply terminal E becomes, for example, +1.2V and UHF1! t
The voltage applied to the A terminal F is, for example, Ov.

As a result, the switching element 3 becomes forward biased and conductive, and the switching element 4 becomes reverse biased and cut off. Therefore, only the field effect transistor l performs high-frequency amplification operation, and the signal obtained by amplifying the V I-I F input signal is passed through the series resonant circuit consisting of the switching element 3, the capacitor 12', the resistor 13', and the high-frequency coil 14. It will be sent to the UHF/VHF combined output terminal G'.

Next, when the UHF signal is selected, the voltage applied to the UHFHF power supply terminal becomes, for example, +12V, and the voltage applied to the VHFi source terminal E becomes, for example, 0. As a result, the switching element 4 becomes forward biased and conductive, and the switching element 3 becomes reverse biased and cut off. therefore,
Only the field effect transistor 2 performs high frequency amplification operation,
A signal obtained by amplifying the tJHF input signal is sent through the switching element 4 to the UHF-VHF composite output terminal G'.

However, in the above configuration, when the V HF input signal is selected, the illumination of the series resonant circuit consisting of the capacitor 12', the resistor 13', and the high frequency coil 14 is
The characteristic becomes as shown in Figure 4, and from 400MHz to 45
It is said that playing cards like region X occur in the 0Ml-1z band! ! ! There was a problem.

The following high-frequency amplification device has been proposed as one that can solve the problems of the high-frequency amplification device shown in FIG. 3 above.

FIG. 5 shows a circuit diagram of a proposed example of a high frequency amplification device.

The high frequency amplification device shown in FIG.
A drain D of a dual gate type field effect transistor 1 for high frequency amplification, to which an input signal is supplied to a gate G, is connected to a VHF power supply terminal E via a switching element 3 and a choke coil IO in this order. In this case, the switching diode constituting the switching element 3 has its cathode connected to the drain D of the field effect transistor 1, and its anode connected to the choke coil io.

Also, the UHF human signal is input from the signal input terminal B to the gate G.
, the drain D of the dual gate type field effect transistor 2 for high frequency amplification, which is supplied to Connected. In this case, the switching diode constituting the switching element 4 has a cathode connected to the drain D of the field effect transistor 2 and an anode connected to the high frequency coil 14.

Further, a high frequency coil 15, 16 and a capacitor 17 are connected in series in this order to the connection point between the switching element 3 and the choke coil 10, and a switching element 20 is connected in parallel with the series circuit of the high frequency coil 16 and the capacitor 17. There is. In this case, the switching diode constituting the switching element 20 has an anode connected to the high frequency coil 1.
6 and its cathode is connected to a capacitor 17.

Then, a resistor 13 is connected between the connection point of the capacitor 17 and the switching element 20 and the ground, and the capacitor 17
and the connection point of the switching element 20 and the choke coil lO
A capacitor 12 is connected between the high-frequency coil 15 and the connection point, and the capacitor 17 and the switching element 20
connection point, choke coil 11 and high frequency coil 14
A parallel circuit of a switching element 19 and a capacitor 18 is connected between the connection point of the switching element 19 and the capacitor 18. In this case, the switching diode constituting the switching element 19 has its anode connected to the connection point between the choke coil 11 and the high-frequency coil 14, and its cathode connected to the connection point between the capacitor 17 and the switching element 2o.

Further, a UHF/VHF composite output terminal G is provided at the connection point between the choke coil 11 and the high frequency coil 14.

Then, when selecting the VHF signal, the switching element 3.20
When the UHF signal is selected, the switching elements 4 and 19 are made conductive and the switching element 3.20 is made to be cut off.

In this case, the conduction/cutoff of the switching elements 3, 4, 19, and 20 is controlled by changing the power supply voltage applied to the VHFHF power supply terminal and the U I (F power supply terminal F). In this case, the voltage applied to the VHFit source terminal E is set to +12V, for example, and the voltage applied to the UHF power supply terminal F is set to Ov, for example, to make the switching element 3.20 conductive and to cut off the switching element 4.19. In addition, the voltage applied to the VHFHF power supply terminal is set to OV, for example, and the voltage applied to the UHF power supply terminal F is set to OV.
By setting the applied voltage to, for example, +12V, switching element 3.20 is cut off and switching elements 4 and 19 are made conductive. In the above, the power supply voltage applied to the VHFHF power supply terminal and the UHF'l source terminal F is as follows:
As in the conventional example, the voltage applied to either one is, for example, +
When the voltage becomes 12V, the other voltage is set to always be 0■.

The configuration other than the above is the same as the conventional example shown in FIG.

The operation of the high frequency amplification device configured as described above will be explained below.

First, a VHF input signal is applied to signal input terminal C, and U
An HF input signal is applied to signal input terminal B.

First, when a VHF signal is selected, the voltage applied to the VHF power supply terminal E becomes, for example, +1.2 V, and the voltage applied to the UHF power supply terminal F becomes, for example, OV.

As a result, switching element 3.20 becomes forward biased and conductive, and switching elements 4 and 19 become reverse biased and cut off. In this case, when the switching element 3 becomes conductive, the field effect transistor 1 operates and V H
The high-frequency amplification of the F input signal is performed, and the signal obtained by amplifying the VHF input signal is sent to the high-frequency coils 14 to 16 and the capacitor 1.
2.1? .

The signal is sent to the UHF/VHF composite output terminal G via a resonant circuit consisting of 18.

Furthermore, due to conduction of the switching element 20 and interruption of the switching element 19, the series circuit of the high frequency coil 16 and the capacitor 17 is short-circuited in an alternating current manner, causing resonance of the resonant circuit consisting of the high frequency coils 14 to 16 and the capacitor 12°17.18. The inductance value becomes small, which moves the trap frequency of the resonant circuit to the UHF band.

Specifically, when the VHF signal is selected as described above, the switching element 20 is conductive and the switching element 19 is disconnected, so that the VHF path and the U
The resonant circuit between the HF paths is represented by the equivalent circuit shown in FIG. 6, in which the high frequency coil 16 and the capacitor 17 are short-circuited in an alternating current manner, and is inserted in series in the VHF signal path. In this case, in the equivalent circuit shown in FIG. ) and capacitors 17+18 cause series resonance, and the resonance point (
The frequency r, ) is in the 430 MHz band. Therefore, the frequency characteristics of the impedance of the resonant circuit in this state are:
It becomes as shown in Fig. 6 fb).

Furthermore, as shown in FIG. 6(C), the pass characteristic at this time has a peak at the frequency f l (430 Mllz band) and a trap at the frequency r 2 (500 Mllz band).

At this time, since the switching element 4 is cut off, the second
The field effect transistor 2 does not operate.

On the other hand, when UHF signal is selected, UHF? t#The voltage applied to the I terminal F becomes, for example, +12V, and the voltage applied to the source terminal E of HF11 becomes, for example, Ov.

As a result, the switching elements 4 and 19 become forward biased and conductive, and the switching elements 3 and 20 become reverse biased and cut off. In this case, when the switching element 4 becomes conductive, the field effect transistor 2 operates and the UHF
The input signal is high-frequency amplified, and the signal obtained by amplifying the UHF input signal is sent to the high-frequency coils 14 to 16 and the capacitor 12.
, 1.7°18 through a resonant circuit consisting of
It will be sent to the HF synthesis output terminal G.

Further, due to the conduction of the switching element 19 and the interruption of the switching element 20, the short circuit of the series circuit of the high frequency coil 16 and the capacitor 17 is stopped, and the high frequency coil 1
The value of the resonant inductance of the resonant circuit consisting of the capacitor 12°17.18 and the capacitor 12°17.18 increases, thereby shifting the trap frequency of the resonant circuit to the VHF band.

Specifically, when the UHF signal is selected as described above, the switching element 19 is conductive and the switching element 20 is disconnected, so the resonant circuit is represented by the equivalent circuit shown in FIG. , this circuit is UHF (8
It will be inserted between the signal path and ground. In this equivalent circuit of FIG. 7+al, the output signal of the second field effect transistor 2 is input to the terminal T of the equivalent circuit of FIG. is VHF- through the high frequency coil 14.
It is sent to the UHF synthesis output terminal G. This V HF/UH
As shown in the equivalent circuit of FIG. 7 (δ), the F composite output terminal G is composed of a series circuit of high-frequency coils 15 and 16, a parallel resonant circuit of a capacitor 12, and a reverse bias capacitor CXI of the switching element 3. A series-parallel resonant circuit will be connected. Therefore, the frequency characteristics of the impedance of the resonant circuit in this state are as shown in Figure 7 (bl), with a resonance point at frequency r1 (430 MIIz band) and an anti-resonance point at frequency f2 (500 MHz band). become.

Therefore, as shown in FIG. 7(e), the pass characteristics at this time are such that there is a trap at the frequency f 2 ' (430Ml (z band)) and a peak at the frequency r2' (500 MHz band).

At this time, since the switching element 3 is cut off, the second
The field effect transistor 1 does not operate.

As described above, when selecting a VHF input signal, the resonant inductance value of the resonant circuit consisting of the high frequency coils 14 to 16 and the capacitors 12 and 17 is reduced (and the trap frequency is increased to move to the UHF band). When selecting a UHF input signal, high frequency coils 14 to 16 and capacitor 12.1?

By increasing the resonant inductance (direction) of the resonant circuit consisting of
It is possible to improve the characteristics of the output signal from the circuit and reduce the loss when coupled to, for example, a double-balanced mixer circuit. That is, according to this proposed example, the frequency range from 400 MHz to 450 Mllz during VHF band reception described in the conventional example
Losses due to belt traps can be reduced.

In the above-mentioned equipment, the VHF route allows broadcasting waves in the VHF band and up to the super high band in the CATV band (90
Mlz~468 Mllz), so when receiving on the VHF route, 400~450MH
If a trap in the z band is inserted into the signal transmission path, it will cause problems, but if it is a trap in the 500 MHz band outside of that band, there will be no problem.Also, when receiving on the UHF path,
It would be bad if a trap was configured in the band (470-770 Mb), but a trap in the 430 MHz band would not be a problem.

[Problem to be solved by the invention]

However, in the high frequency amplifier of this proposed example, when the UHF band is selected, the gain in the 480 MHz band becomes too large, and second-order distortion occurs in the high frequency amplifier itself and the mixer circuit in the subsequent stage, and the intermediate frequency is reduced to, for example, 960 Mb. There was a problem in that the influence was particularly large when the setting was set to .

The present invention provides a high frequency amplification device that can reduce loss when coupling to a mixer circuit and can also reduce second-order distortion when selecting a UHF input signal.

(Means for Solving the Problems) The high frequency amplification device of the present invention converts high frequency human power signals into VHF
Distributed into two systems: input signal and UHF input signal,
The HF input signal and the UHF input signal are individually amplified and output in common.

For this purpose, one end of the first amplifying transistor for the VHF input signal is connected to the first power supply via the first switching element and the first choke coil in this order, and
One end of the second amplifying transistor for human input signals is connected to the second power source via a second switching element, a series circuit of the first high-frequency coil, and a second choke coil in this order.

Further, one end of a series circuit of a second high-frequency coil and a third switching element is connected to a connection point of the first switching element and the first choke coil, and a series circuit of the second high-frequency coil and the third switching element is connected. One end of the parallel circuit of the fourth switching element and the capacitor is connected to the other end of the circuit, and the second choke coil and the second
The other end of the fourth switching element and the parallel circuit of the capacitor is connected to the connection point between the switching element and the series circuit of the first high-frequency coil.

Furthermore, U
An HF/VHF composite output terminal is provided.

[For production]

In the configuration of the present invention, when the V HF input signal is selected, the first and third switching elements are made conductive, and the second and fourth switching elements are cut off. In this case, when the first switching element becomes conductive, the first amplification transistor operates and the V IIF input signal is high-frequency amplified. Furthermore, due to the conduction of the third switching element and the interruption of the fourth switching element, a resonance circuit consisting of the second high-frequency coil and stray capacitance provides a pass characteristic with peaking in the frequency band of 350 MHz to 450 MHz.

On the other hand, when selecting a UHF manual signal, the second and fourth switching elements are made conductive, and the first and third switching elements are cut off.

In this case, the second switching element becomes conductive, so that
The second amplification transistor operates to high-frequency amplify the UHF input signal. Furthermore, due to the conduction of the fourth switching element and the interruption of the third switching element, no resonant circuit is formed, and the pass characteristic becomes flat.

〔Example〕

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

FIG. 1 shows a circuit diagram of a high frequency amplifier according to an embodiment of the present invention.

The high frequency amplifier shown in Fig. 1 has a VHF signal from the signal input terminal C.
The drain D of the first field effect transistor 1 for high frequency amplification of dual gate type whose input signal is supplied to the gate Gl is connected to the VHFHF power supply terminal via the first switching element 3 and the first choke coil 10 in this order. It continues. In this case, the switching diode constituting the switching element 3 has its cathode connected to the drain D of the field effect transistor l, and its anode connected to the choke coil 10.

Further, the UHF input signal from the signal input terminal B is input to the gate G,
The drain of the dual-gate type second field effect transistor 2 for high frequency amplification supplied to through υ
Connected to HF power supply terminal F. In this case, the switching diode constituting the switching element 4 has a cathode connected to the drain of the field effect transistor 2 and an anode connected to the high frequency coil 14.

Further, one end of a series circuit of the second high frequency coil 15 and the third switching element 2G is connected to the connection point between the switching element 3 and the choke coil IO. In this case, one end of the high frequency coil 15 is connected to the connection point between the switching element 3 and the choke coil IO, and the other end of the high frequency coil 15 is connected to the anode of the switching diode constituting the switching element 20.

Then, the high frequency coil 15 and the switching element 20
Connect a resistor 13 between the other end of the series circuit and ground,
The other end of the series circuit of the high frequency coil 15 and the switching element 20 and the choke coil 11 and the high frequency coil 14
A parallel circuit of a fourth switching element 19 and a capacitor 18 is connected between the connection point and the connection point. In this case, the switching diode constituting the switching element 19 is an acx2 whose anode is connected to the connection point of the choke coil 11 and the high-frequency coil 14, and whose cathode is connected to the other end of the series circuit of the high-frequency coil 15 and the switching element 20. is the stray capacitance.

Further, a UHF/VHFHF composite output terminal is provided at the connection point between the choke coil 11 and the high frequency coil 14.

and V) the switching element 3.2 when selecting the IF signal.
0 is made conductive and the switching element 4.19 is cut off, and when the UHF signal is selected, the switching element 4.19 is turned on.
The switching element 3.20 is made conductive and the switching element 3.20 is cut off.

In this case, conduction/cutoff of the switching elements 3, 4, 20.19 is controlled by changing the power supply voltage applied to the VHFHF power supply terminal and the UHF power supply terminal F. Specifically, by setting the voltage applied on the VHFHF power supply terminal to, for example, +12V and setting the voltage applied to the UHF power supply terminal F to, for example, QV, the switching element 3.20 is made conductive, and the switching elements 4 and 1 are made conductive.
9 is cut off. Further, by setting the voltage applied on the VHFHF power supply terminal to, for example, Ov and setting the voltage applied to the UHF power supply terminal F to, for example, +12V, the switching elements 3 and 20 are cut off, and the switching elements 4 and 1
9 becomes conductive. In the above, the power supply voltages applied to the VHFHF power supply terminal and the UHFi source terminal F are set so that when the voltage applied to either one is, for example, +12V, the voltage to the other is always QV.

The configuration other than the above is the same as the conventional example shown in FIG.

The operation of the high frequency amplification device configured as described above will be explained below.

First, a VHF input signal is applied to signal input terminal C, and U
An HF input signal is applied to signal input terminal B.

First, when the VHF signal is selected, the voltage applied to the V)IF power supply terminal becomes, for example, +12V, and the voltage applied to the UHF power supply terminal F becomes, for example, 0.

As a result, the switching elements 3 and 20 become forward biased and conductive, and the switching element 4.19 becomes forward biased and cut off. In this case, when the switching element 3 becomes conductive, the field effect transistor l operates and the VHF
The input signal is high-frequency amplified, and the signal obtained by amplifying the VHF input signal is sent to the high-frequency coil 14, 15 and the capacitor 18.
The signal is sent to the LIHF-VHF composite output terminal G via a circuit consisting of the following.

Also, due to the conduction of the switching element 20 and the interruption of the switching element 19, the high frequency coil 15 and the stray capacitance IC
x□ constitutes a series resonant circuit, and its resonant frequency is 35
Since it is in the 0 to 450 MHz band, the transmission characteristic is 350 MHz.
Peaking occurs in the llz to 450 MHz band, and no trap occurs in the 450 MHz band as in the conventional example.

At this time, since the switching element 4 is cut off, the second
The field effect transistor 2 does not operate.

On the other hand, when the UHF signal is selected, the voltage applied to the UHF power supply terminal F becomes, for example, +12V, and the voltage applied to the VHFit source terminal E becomes, for example, OV.

As a result, the switching elements 4 and 19 become li[biased and conductive, and the switching elements 3 and 20 become reverse biased and cut off. In this case, when the switching element 4 becomes conductive, the field effect transistor 2 operates and the U
The HF input signal is high-frequency amplified, and the signal obtained by amplifying the UHF input signal is sent to the UHF/VHF composite output terminal G via a circuit consisting of high-frequency coils 14, 15 and capacitor 18.

Furthermore, due to the conduction of the switching element 19 and the interruption of the switching element 20, the series capacitance of the reverse bias capacitance of the switching element 2o and the stray capacitance Cx□ is connected between the VHF-U HF composite output terminal G and the ground. As a result, the passage characteristics become flat without traps as shown in FIG.

At this time, since the switching element 3 is cut off, the second
The field effect transistor 1 does not operate.

As mentioned above, when selecting a VHF input signal, the resonance between the high frequency coil 15 and the stray capacitance causes the pass characteristic to be 350 MHz.
The characteristic peaks in the frequency band of 450 MHz to 450 MHz, and there is no trap in the 450 MHz band as in the conventional example, and when a UHF input signal is selected, no resonant circuit is formed, resulting in a flat pass characteristic. Therefore, both when selecting a VHF input signal and when selecting a UHF human input signal, it is possible to improve the characteristics of the output signal from the VHF/UHF combined output terminal and reduce loss when coupled to, for example, a double-balanced mixer circuit. That is,
According to this embodiment, it is possible to reduce the loss due to traps in the 400 MHz to 450 MHz band during VHF band reception.

〔Effect of the invention〕

According to the high frequency amplification VtI of the present invention, one end of the series circuit of the second high frequency coil and the third switching element is connected to the connection point of the first switching element and the first choke coil, and the second high frequency coil and the other end of the series circuit of the third switching element is connected to one end of the parallel circuit of the fourth switching element and the capacitor, and the series circuit of the second switching element and the first high-frequency coil and the second choke coil The other end of the parallel circuit of the fourth switching element and the capacitor is connected to the connection point with U, and the other end of the parallel circuit of the fourth switching element and the capacitor is connected to the connection point of the second choke coil with the series circuit of the second switching element and the first high-frequency coil.
An HF/VHF combined output terminal is provided, and when a VHF signal is selected, the third switching element is made conductive and the fourth switching element is cut off, and when a UHF signal is selected, the third switching element is made conductive.
Since the second switching element is cut off and the fourth switching element is made conductive, when selecting a VHF input signal, the resonance between the second high frequency coil and the stray capacitance causes the pass characteristic to change in the frequency band of 350M11z to 450MHz, for example. It has a peaking characteristic, and there is no trap in the 450M1lz band like in the conventional example, and when a UHF input signal is selected, a resonant circuit is not formed.
It has a flat passing characteristic. Therefore, both when VHF input signal is selected and when UHF input signal is selected, VHF-LJ
It is possible to improve the characteristics of the output signal from the HF synthesis output terminal and reduce the loss when coupled to the mixer circuit.

In addition, since the passing characteristic when selecting a UHF input signal is flat, when selecting a UHF human input signal, for example, 4
The gain in the 80 MHz band does not become too large,
A high frequency amplification device with excellent second-order distortion characteristics can be obtained. Therefore, there is no problem in setting the intermediate frequency to 960 MHz.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a high frequency amplification device according to an embodiment of the present invention, and FIG. 2 is a UHF circuit diagram of the high frequency amplification device of FIG.
Figure 3 is a circuit diagram of a conventional high frequency amplification device; Figure 4 is a diagram of passage characteristics of a resonant circuit in the conventional example shown in Figure 3; Figure 5 is a diagram of a high frequency amplification device. Figure 6 (Jl) is an equivalent circuit diagram of the resonant circuit when selecting the VHF band of the high frequency amplifier shown in Figure 1, and Figure 6 (bl is the resonance circuit diagram of Figure 6 (a)) Figure 6 (C) is a frequency characteristic diagram of the impedance of the circuit, Figure 6 (C) is a passage characteristic diagram of the resonant circuit in the figure (al), and Figure 7 (a) is the frequency characteristic diagram of the resonant circuit of the high frequency amplifier shown in Figure 1 when the UHF band is selected. Equivalent circuit diagram, Figure 7 (
bl is an impedance frequency characteristic diagram of the resonant circuit shown in tal in the same figure, and FIG. 2 field effect transistor, 3... first switching element, 4... second switching element, lO... first
Chirakcoil, 11...Second Thousand En-kucoil,
13...Resistor, 14...First high frequency coil, 15
...Second high frequency coil, 18...Capacitor, 1
9... Fourth switching element, 20... Third switching element, E... VHF power supply terminal, F...U
HFtHF power supply terminal...UHF-VHF combined output terminal Fig. 2B Fig. Rock diagram

Claims (1)

[Claims] One end of the first amplification transistor for the VHF input signal is connected to the first power supply via the first switching element and the first choke coil in this order, and the second amplification transistor for the UHF input signal is connected to the first power supply through the first switching element and the first choke coil in this order. One end is connected to a second power source via a series circuit of a second switching element and a first high-frequency coil, and a second choke coil in this order, and the first switching element and the first choke coil One end of the series circuit of the second high frequency coil and the third switching element is connected to the connection point of the fourth switching element and the other end of the series circuit of the second high frequency coil and the third switching element. One end of the parallel circuit of the capacitor is connected, and a parallel circuit of the fourth switching element and the capacitor is connected to the connection point between the series circuit of the second switching element and the first high-frequency coil and the second choke coil. The other end is connected to the UH
An F/VHF synthesis output terminal is provided, and when a VHF signal is selected, the first and third switching elements are made conductive, and the second and fourth switching elements are cut off, and when a UHF signal is selected, the second and fourth switching elements are made conductive. A high frequency amplifying device characterized in that a switching element is made conductive and the first and third switching elements are cut off.