JPS614308A - Switching device of high frequency circuit - 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 the Invention The present invention relates to a switching device for a high frequency amplifier circuit used for switching between VHF and UHF in a tuner.

Conventional configuration and its problems Recently, high frequency amplifiers using field effect transistors (hereinafter abbreviated as FET) are often used, but when used as an RF amplifier for a tuner, VHF and U
It is necessary to switch the HF output according to each reception time.

FIG. 1 shows a conventional example of a switching device. In FIG. 1, 1 is an amplifying transistor for UHF, 5 is an amplifying transistor for VHF, 2 and 6 are respective switch diodes, 3,
7 is each load choke, 4 is VHF output and UHF
This is a coupling capacitor that connects the output. UH from the terminal person
When receiving F, a power supply voltage is supplied, and when receiving VHF, it is grounded through a resistor of several Ω to turn off diode 2. Terminal B is a power supply terminal during VHF reception and operates in the same way as the terminal terminal. Terminal C is a common RF output terminal and is coupled to the next stage mixer, etc. Generally, diodes 1 and 2 and transistors 5 and 6 are contained within an integrated circuit, and choke 3
, 7 and the coupling capacitor 4 are configured externally.

In the amplifier configured as above, VHF and UH
This is possible only when F is a broadband amplification and a choke load.

However, the gain is low in the case of wideband, especially in UHF.
In this case, it is difficult to obtain a gain like a tuned amplifier.

Therefore, as shown in FIG. 2, there are cases where it is desired to configure the load circuits 3 and 8 so as to have a slight tuning characteristic near the center of the UHF band. In that case, in the position of diode 2 in Fig. 1, the influence of the tuning circuit consisting of coil 3 and capacitor 8 during VHF reception is reduced to f3'''', o'r, j (Ida
E 2 '@ 't' Icy: Lftc l-”7
-"A switch circuit consisting of 2 and a resistor 9 can be considered.

In this case, coupling between UHF and UHF can be avoided, but a switch current is required, and in particular, in order to reduce loss during conduction, a current comparable to that flowing through the transistor is required. Also, if the output impedance of the transistor is high,
Due to the distributed capacitance caused by leads and foils caused by inserting a switch circuit, there is a drawback that loss occurs in the UHF band.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems, and aims to provide a switching device that is not affected by each other even when a tuned load is applied and that has less loss.

Structure of the Invention The switching device according to the present invention is such that one switch diode is inserted between a load choke and a coil constituting a tuning circuit inserted at the output terminal of at least one transistor of two high-frequency amplifier circuits. Therefore, each signal can be extracted without being influenced by each other.

Description of examples Examples of the present invention will be described below.

Figure 3 shows a circuit diagram of a high frequency amplifier switching device according to an embodiment of the present invention.
, FIT for F amplification, 18 is FET for VHF amplification, 12 and 19 are respective switching diodes, 14 is a tuning coil, 15 is a tuning capacitor, 16 is a DC cut capacitor, 13 is for U HF -7-= s-kucoil,
20 is a choke coil for VH1r, and 17 is a coupling capacitor.

The operation of the switching device configured as described above will be explained below. In FIG. 3, circuits 14 and 16 and a choke 13 are connected to the output side load of the UHF amplifier section to provide a tuning characteristic near the center of the UHF band.
One switch diode 12 is connected between the middle tap point of the tuning coil 14 and the choke 13. Therefore, during UHF reception, the switch diode 12 becomes conductive, and the characteristics of the tuned circuit consisting of the coil 14 and capacitor 15 appear at the output terminal C via the coupling capacitor 17.

At this time, since the switch diode 19 is off, it is not affected by the transistor 18.

Further, when receiving VHF, the diode 12 is turned off, the tuning circuit is disconnected, and only the choke 13, which has no effect on the characteristics, is connected as a load, so that there is no influence of the UHF circuit even when receiving VHF.

Furthermore, since the load coil 14 is tapped down and connected to the switch diode, the impedance after the switch diode is low, and losses due to routing are significantly reduced.

In this embodiment, only the UHF section is provided with a tuning circuit, but even if the UHF section is also provided with a tuning circuit, it can be configured with the same circuit as the UHF section.

FIG. 4 is a configuration diagram when this circuit is integrated, and the inside of the diagonal frame is the built-in part. Figure 4 is the embodiment of Figure 3,
A shows the case where a tuning circuit is also provided in the UHF section.

Effects of the Invention According to the present invention, when the outputs of two high-frequency amplifiers are made common and taken out as one output, by inserting a switch diode between the tuning circuit and the load choke, according to the present invention, two The outputs of the two amplifier circuits can be taken out without affecting each other.

In addition, since the amplification transistor's voltage current and swing current are shared, the current of the ode can be saved.

Furthermore, the tap-down load allows a switching circuit to be realized with low impedance, reducing loss, and since the impedance of the tuning circuit increases, for example, a variable tuning circuit can be constructed by using capacitor C in the tuning circuit as a varicap. High Q tuning characteristics can be obtained.

Note that by incorporating the transistor and switch diode of the above circuit into an IC, it is possible to reduce the cost, minimize the mounting distance, and further reduce loss. Further, by separately providing the output terminal of the transistor and the cathode terminal of the switch diode, the tuning circuit can be arbitrarily selected.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional switching device that switches between two high-frequency amplifiers, Fig. 2 is a circuit diagram of a conventional switching device when the output of the high-frequency amplifier is a tuned load, and Fig. 3 is a circuit diagram of a conventional switching device for switching between two high-frequency amplifiers. Circuit diagram of high frequency circuit switching device in one embodiment, No. 4
Figures a and b are diagrams showing the configuration when the same device is integrated into an integrated circuit. 11.18...Transistor for high frequency amplification, 1
2゜19...Switch diode, 14...
...Tuning coil, 13.20...Load choke coil. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 4

Claims (2)

[Claims] (1) Connect one end of the coil to the output of at least one transistor of the two high-frequency amplifiers, connect the other end of the coil to AC ground, and connect any tap position of the coil to the cathode of the switch diode, A first terminal is connected between the anode of the diode and the power supply terminal of the transistor.
A high frequency circuit switching device comprising: a choke coil connected to the second choke coil; and an anode of the diode connected to the intersection of the anode of a switch diode connected to the other transistor via a coupling capacitor and a second choke coil. (2) A high-frequency amplification transistor and a switch diode are built into an integrated circuit, and the output terminal of at least one transistor and the cathode terminal of the switch diode are separately drawn out to the outside. High frequency circuit switching device.