JPS58124307A - High frequency switching device - Google Patents

Abstract

PURPOSE:To eliminate oscillation when an amplifier is not in use and to save electric power by performing switching between a function for deciding on whether a signal passes through or by-passes an amplifying circuit and a bias for operating the amplifying circuit through the operation of the same switch. CONSTITUTION:For a signal having a low level, terminals 1-3 and 1'-3' are connected together through the switching of the changeover switch SW4 to interpose resistances 5 and 6 in series between a power source VCC and a ground point through the terminal of the SW4, and then an amplifying transistor TR3 is applied with a prescirbed bias to start amlifying the input signal from the terminal 1, thereby outputting the resulting signal from a terminal 2. For a signal having a high level, terminals 1-2 and 2'-1' are connected through the switch SW4 and then the input signal by-passes the amplifying circuit and is outputted from the output terminal. In this case, the amplifying circuit is placed in a cut-off state by disconnecting the resistance 5 to eliminate oscillation, thereby saving electric power.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency switching device including a high frequency amplifier circuit inserted into a path for supplying high frequency signals such as television signals.

Among the devices having the above-mentioned high-frequency amplification circuit, there is a structure in which a switch is used to select between a circuit for amplifying the signal and a circuit for detouring the signal without passing through the amplification circuit. This is to amplify the signal when the signal is weak to enable good reception, and when the signal is strong to prevent cross-modulation and intermodulation occurring from the amplifier circuit. Good reception can be achieved regardless of the strength of the signal. An example of a conventional circuit in this case is shown in FIG. In the figure, 1 is a signal input terminal, 2 is an output terminal, 3 is a high-frequency amplification transistor, and 4 is a changeover switch. When the input signal is strong, the changeover switch 4 is connected to the terminals ■-■, ■'-
(2) is switched to connect (2); at this time, a signal enters from input terminal 1, passes through the path of terminals (2)-(2)-(2)-(2), is output to output terminal 2, and bypasses amplifying transistor 3. Therefore, since no signal enters the amplifier circuit, no intermodulation or cross modulation occurs.

On the other hand, when the signal is weak, selector switch 4 is connected to terminal ■-■
, ■'-■' are switched to connect. At this time, the signal enters from the input terminal 1 and becomes a path from the terminals ■-■-transistor 3 to the terminals ■'-■'-output terminal 2, and is amplified by the transistor 3. Here, the transistor 3 is given a predetermined bias by resistors 5, 6.7, 3 and an inductance 8. Further, since the input signal is weak, cross-modulation and intermodulation occurring in the transistor 3 are extremely small and do not cause any trouble.

As described above, although the configuration shown in FIG. 1 allows good reception regardless of the strength of the signal by operating the selector switch 4, it has the following drawbacks. In other words, when the signal is strong, changeover switch 4 is set to terminal ■
If you switch to connect −■, ■′−■′, no signal will enter the amplifier circuit, but the amplifier transistor 3
is activated by a resistance 6°6.7 and an inductance 8. Here, terminals ■ and ■′ are terminals ■.

It exhibits high impedance because it is not connected to
Depending on the arrangement and position of the resistors 5, 6, 7, inductance 8, and capacitor 9 that make up the amplifier circuit, as well as the coupling between components, there is a very high possibility that the amplifier circuit will go into an oscillating state. However, it is necessary to take into account the arrangement and shape of each component that makes up the amplifier circuit, and it also has the disadvantage that there is loss because power is supplied to circuits that are not in use.

The present invention eliminates the above-mentioned drawbacks of the conventional technology, and at the same time switches the selector switch so that the signal enters the high-frequency amplifier circuit, the high-frequency amplifier circuit is set to the operating state, and the signal bypasses the amplifier circuit and is supplied to the output terminal. When this happens, the amplifier circuit is set to a cut-off state.

An embodiment of the present invention will be described below with reference to FIG. In the figure, elements that perform the same functions as those in FIG. 1 are given the same numbers.

The difference between FIG. 2 and FIG. 1 is that the bias resistor 5 inserted between the base of the amplification transistor 3 and the power supply (Vcc) terminal in FIG. The other end of this resistor 6 is connected to the terminal (3) of the changeover switch 4. A power terminal Vcc is connected to the connection point between the resistor 5 and the inductance 8.

In the above configuration, when the signal is weak, selector switch 4
Switch to connect terminals ■−■ and ■′−■′.

At this time, resistors 6 and 6 are connected in series between the power supply terminal Vcc and the ground through terminals ■-■ of the changeover switch 4, and the amplifying transistor 3 is given a predetermined bias and is in an operating state. The output signal is amplified and supplied to output terminal 2.

On the other hand, when the signal is strong, selector switch 4 is connected to terminal ■-■
, ■'-■' are switched to connect.

At this time, the signal is at the terminal of selector switch 4 ■−■−■′−■
' and is sent to the output terminal 2, bypassing the amplifier circuit. Then, since the resistor 5 is disconnected, the amplifier circuit does not operate and enters a cut-off state.

As described above, according to the present invention, the amplifier circuit can be used by operating the function of switching between passing through the amplifier circuit or bypassing the amplifier circuit and the switching of the bias for operating the amplifier circuit with the same switch. There is no need for any means to eliminate the oscillation state when the device is not in use, and power is not wasted.

[Brief explanation of the drawing]

6 〆＼ Figure 1 is a circuit diagram of a conventional high frequency switching device, Figure 2 is a circuit diagram of a conventional high frequency switching device.
The figure is a circuit diagram of a high frequency switching device in one embodiment of the present invention. 1...Input terminal, 2...Output terminal, 3
...Transistor for high frequency amplification, 4...
・Choice switch.

Claims (1)

[Claims] A changeover switch is provided to select a high-frequency amplification circuit that amplifies a high-frequency signal and a circuit that bypasses this high-frequency amplification circuit, and when the high-frequency signal passes through the high-frequency amplification circuit with this changeover switch, this high-frequency amplification circuit is in the operating state. and a high frequency switching device, wherein a bias is set so that the high frequency amplification circuit is in a non-operating state when the high frequency amplification circuit is detoured.