JPH0250645B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 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 using this as an RF amplifier for a tuner, VHF and UHF outputs are It is necessary to switch depending on the time of reception.

FIG. 1 shows a conventional example of a switching device. In Figure 1, 1 is a UHF amplification transistor, 5 is a VHF amplification transistor, 2 and 6 are respective switch diodes, 3 and 7 are respective load chains,
4 is a coupling capacitor that connects the VHF output and UHF output. Power supply voltage is supplied from terminal A when receiving UHF, and when receiving VHF it is grounded through a resistor of several kilohms to turn off diode 2. Terminal B is
This is the power supply terminal when receiving VHF and performs the same operation as terminal A. Terminal C is a common RF output terminal and is coupled to the next stage mixer, etc. Generally, the diodes 1 and 2 and the transistors 5 and 6 are contained within the integrated circuit, while the diodes 3, 7 and the coupling capacitor 4 are constructed externally.

In the amplifier configured as above, VHF
and UHF is only possible with wideband amplification and high load. However, in the case of a wide band, the gain is low, and in the case of UHF in particular, 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,
Since the position of diode 2 in FIG. 1 is affected by the tuning circuit consisting of coil 3 and capacitor 8 during VHF reception, a switch circuit consisting of diode 2 and resistor 9 shown in FIG. 2, for example, can be considered.

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

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 during a tuned load and has less loss.

Structure of the Invention A switching device according to the present invention is such that one switch diode is inserted between a load chain 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.

FIG. 3 shows a circuit diagram of a high frequency amplifier switching device in an embodiment of the present invention.

In the figure, 11 is a UHF amplification FET, and 18 is
VHF amplification FET, 12 and 19 are respective switching diodes, 14 is a tuning coil, 15 is a tuning capacitor, 16 is a DC cut capacitor,
Reference numeral 13 designates a UHF chiyoke coil, 20 a VHF chiyoke coil, and 17 a coupling capacitor.

The operation of the switching device configured as described above will be explained below. In FIG. 3, circuits 14 and 15 and a chain 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 switch yokes 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, the switch diode 19 is off, so the transistor 18 is not affected.

Also, when receiving VHF, diode 12 is turned off,
The tuning circuit is disconnected and only the chain 13, which has no effect on the characteristics, is connected as a load, so VHF
This means that the signal will not be affected by the UHF circuit during reception.

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 greatly reduced.

In this embodiment, only the UHF section is provided with a tuning circuit, but the VHF section may also be provided with a tuning circuit and 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 4b is the third
In the illustrated embodiment, a shows a case in which a tuning circuit is also provided in the VHF section.

Effects of the Invention As described above, according to the present invention, when the outputs of two high-frequency amplifiers are shared and taken out as one output, by inserting a switch diode between the tuning circuit and the load chain, the two amplification The outputs of each circuit can be taken out without affecting each other.

Furthermore, since the power supply current of the amplifying transistor and the switch current are shared, the current of the switch diode can be saved.

Furthermore, the tap-down load allows a switching circuit to be realized with low impedance, reducing loss, and conversely increasing the impedance of the tuning circuit. High tuning characteristics can be obtained.

Note that by incorporating the transistors and switch diodes in the above circuit into the IC, it is possible to reduce the cost, minimize the mounting distance, and further reduce loss. Furthermore, 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. FIGS. 4a and 4b, which are circuit diagrams of a high-frequency circuit switching device according to an embodiment, are diagrams showing the configuration when the same device is integrated into an integrated circuit. 11, 18...High frequency amplification transistor, 1
2, 19... Switch diode, 14... Tuning coil, 13, 20... Load chain coil.

Claims (1)

[Claims] 1. One end of the coil is connected to the output of at least one transistor of two high-frequency amplifiers, the other end of the coil is grounded in an alternating current manner, and any tap position of the coil and the cathode of the switch diode are connected. A first switch coil is connected between the anode of the diode and the power supply terminal of the transistor, and the anode of the switch diode and the second switch coil are connected to each other, and the anode of the diode is connected to the other transistor via a coupling capacitor. A high frequency circuit switching device connected to the intersection of 2. The high frequency amplifier according to claim 1, wherein a high frequency amplifying transistor and a switch diode are built into an integrated circuit, and the output terminal of at least one of the transistors and the cathode terminal of the switch diode are separately drawn out. Circuit switching device.