JPS62120106A - High frequency amplifier device - Google Patents

Abstract

PURPOSE:To reduce the deterioration in the gain at the reception of a high frequency band signal by coupling cross points both frequency choke coils and switching diodes by a choke coil at a high frequency band and a peaking circuit at a low frequency band. CONSTITUTION:Cross points between both high/low frequency choke coils 105, 106 and switch diodes 103, 104 are coupled by a serial/parallel circuit comprising a coil 110 and a capacitor 107 whose constants are selected acting like a choke coil at a high frequency band and acting like a peaking circuit by the series resonance at a low frequency band. A VHF band setting signal is fed from a terminal 1A and fed to the next stage from a terminal 1E via the capacitor 107, the resistor 111 and the coil 110. A UHF band signal is subjected to the effect of a stray capacitance 109, but since the inductance of the coil 110 is sufficiently larger to the UHF band signal, a stray capacitance 108 is shut from the signal path.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high frequency amplification device used in television receivers and the like.

BACKGROUND OF THE INVENTION In recent years, with the development of the CATU band, an increasing number of high-frequency amplification devices are used in two or more frequency bands.

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

FIG. 2 shows a conventional high frequency amplification device.

In FIG. 2, 2A and 2B are input terminals for different bands. High frequency amplifiers 201 and 202 amplify signals in different bands (here, VHF band and UHF band). 203 and 204 are switching diodes, which are connected in series to the drains (or collectors) of FET (or bipolar) transistors in the high-frequency amplifiers 201 and 202, and supply each high-frequency amplified signal to the subsequent stage. is turned on/off.

Reference numerals 206 and 206 denote choke coils, which are connected to the drains (or collectors) of FET (or bipolar) transistors of the high-frequency amplifiers 201 and 202 via switching diodes 203 and 204f, 1, respectively. 2C and 2D are the respective power supply terminals; for example, when receiving VHF, terminal 2C is at high level and terminal 2D is at low level, and when receiving UHF, terminal 2D is at high level and terminal 2C is at low level. become the level.

2o is a coupling capacitance, and the signals of different bands as mentioned above are supplied to the next stage from one of the selected signal 1 output terminals 2E. 208 and 209 indicate stray capacitances existing in the circuit.

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

First, when receiving the first band (here, VHF band), the terminal 2C is set to a high level and the terminal 2D is set to a circle level power supply voltage, so the high frequency amplifier 2o1, switching diode 203, choke coil 206 The signal path supplied from terminal 2A is turned on, and the signal path supplied from terminal 2B is turned off. As a result, only the VHF band signal is amplified and supplied to the next stage via the coupling capacitor 7 from the terminal 2E. At this time, the switching diode 204 becomes reverse biased to prevent the VHF band signal from attenuating.

When receiving the second band (here, the UHF band), contrary to the above case, terminal 2D is set to a high 17 bell level, terminal 2C is set to a low level power supply voltage, and the The signal on the line is amplified and supplied to the next stage from terminal 2E. (For example, see Japanese Patent Application Laid-Open No. 69-36431.) Problems to be Solved by the Invention However, in the above configuration, the stray capacitance 208
．． When 209 is 0.5 to 1 pF 8 degrees, there is a problem that the stray capacitance is twice as much as that of a single amplifier, and the gain in the high frequency UHF band is degraded by 3 to 4 dB. .

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a device that can switch signals in two bands and combine them into a single path without causing gain deterioration in high frequency bands. It is.

Means for Solving the Problems In order to solve the above problems, the high frequency amplification device of the present invention has a drain (or collector) of a FET (or bipolar) transistor used in two high frequency amplifiers that amplify different bands. is connected to a choke coil connected to each power supply circuit via a switching diode, and the intersection between the two choke coils and the switch diode acts as a choke coil for high frequency bands, and the frequency For the round band, coupling is performed by a series-parallel circuit consisting of a coil with a constant set to act as a peaking circuit due to series resonance, a capacitance, and a resistor connected in parallel to the coil.

Effect of the Invention With the above-described configuration, the present invention eliminates the influence of stray capacitance generated in the low frequency band thread or choke coil, which conventionally causes gain deterioration, when attempting to receive a high frequency band. can be reduced by the coupling coil, and deterioration in gain when receiving signals in a high frequency band can be reduced.

Embodiment Hereinafter, a high frequency amplification device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit of a high frequency amplification device according to an embodiment of the present invention. In Figure 1, 101°102 is F
A high frequency amplifier using ET (or bipolar) transistors, 103 and 104 are switching diodes connected to their respective drains (or collectors),
105 and 106 are respective switching diodes 1
03, 104 and a choke coil connected between the power supply terminal, 107 is a coupling capacitance, 108 and 109 are stray capacitances existing in the circuit, 110 is a coupling inductance, 111
is the damping resistance. 1A is an input terminal for a signal in a low frequency first band (here, VHF band), 1B is an input terminal for a signal in a high frequency second band (here, UHF band), and 1C is a reception terminal for VHF band. The power supply (VHF
1D is a power supply (UHF power) terminal which becomes low level when receiving the UHF band and becomes high level when receiving the VHF band, and 1E is a signal output terminal.

V) (The signal in the F band is amplified through a thread in which the high frequency amplifier 101, the switching diode 1o3, and the choke coil 106 are connected in series. The signal in the UHF band is amplified through the high frequency amplifier 102, the switching diode 104, and the choke coil 106. The coil 106 is amplified through the threads connected in series.The switch diodes 103 and 104 of the two threads and the choke coils 10S and 10S
The intersection points are coupled by a series-parallel circuit consisting of a coupling capacitor 107, a coupling coil 110, and a resistor 111 in parallel with the coupling coil 110. 108 and 109 are stray capacitances existing in the circuits of each yarn path.

Regarding the high frequency amplification device configured as above, the first
The operation will be explained using diagrams.

First, a VHF band signal is supplied to the high frequency amplifier 101 from the terminal 1A. The high frequency amplifier 101 is normally F
The ET is constructed using a bipolar transistor, and its drain (or collector) is connected to a choke coil 106 via a switching diode 103. When the power supply terminal 1C becomes a high level, a current of 1liIi flows through this thread, and the current Vl (F signal is amplified, and VH is applied to the intersection of the switch diode 103 and the choke coil 105.
F signal is output. This signal is supplied to the next stage from the output terminal 1E via the coupling capacitor 107, the resistor 111, and the coupling coil 110. At this time, the resonant frequency J to H of the series resonant circuit consisting of the coupling capacitor 107 and the coupling coil 110
By selecting the signal in the F band, the signal in the VHF band can be supplied to the next stage from the terminal 1E without being attenuated.

At this time, since the terminal 1D is at a low level, the switch diode 104 is reversed); the signal attenuation at the output terminal 1E is due to the parallel capacitance of the stray capacitances 108 and 109, but the capacitance value is small and V
Since the frequency is low in the HF band, the amount of attenuation due to the parallel capacitance is not a problem.

On the other hand, when receiving a signal in the UI (F band), the power supply terminal 1D is at a high level and the terminal 1C is at a low level.
A current flows through the choke coil 106, and the UHF band signal is amplified and output to the intersection of the switching diode 104 and the choke coil 106. in this case,
UHF band signals are affected by stray capacitance 109,
Since the inductance of the coupling coil 110 is sufficiently large for UHF band signals, this reduces the stray capacitance 10
The current is cut off from the signal path, and the influence of stray capacitance 1j (108 can be extremely reduced). A capacitor of 221 F as the coupling capacitance 107, a coil with a diameter of 3 mm and 7 turns as the coupling coil 10, and a resistor 11.
By using Ω for 2.2 as 1, UH
The gain in the F band (470 to 706 degrees) could be improved by 3 to 4 dB.The improvement effect was particularly large when coupling by high impedance.

Although the above embodiments have been described for the VHF/UHF band, the present invention can also be implemented for amplifier circuits for two or more bands with a large difference in frequency.

As described above, according to the present invention, low frequency (VHF)
For high frequency bands (such as UHF bands), a series resonant circuit is formed, and for high frequency bands (such as UHF bands), a series circuit with an inductance and a capacitance is set to act as a choke coil. By doing so, it is possible to simultaneously improve the gain in the high frequency band without impairing the gain in the low frequency band.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a high frequency amplification device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional high frequency amplification device. 101.102...High frequency amplifier, 103゜1
04...Switching diode, 106°1
06...Choke coil, 1o7...
Coupling capacity, 110...Coupling Koinope 111...
...Coupling resistance.

Claims (1)

[Claims] The drains (or collectors) of each FET (or bipolar) transistor that amplifies two systems of signals with different frequency bands are connected to a power supply terminal via a switching diode and a choke coil, respectively. The points of intersection with the choke coils are coupled by a series resonant circuit using an inductance that resonates in a low frequency band and has high impedance in a high frequency band, and a damping resistor is inserted in parallel to the coupling inductance. A high-frequency amplification device characterized by connecting to lower the Q of series resonance and widening the band.