JPH04116441U - switching circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a switching circuit with low circuit loss that performs switching with a weak high-frequency signal. [Structure] A common bias resistor is provided to apply a bias to the bases of the switching diode and the high-frequency transistor, and a drive circuit is provided to control the application of bias to the bias resistor.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention relates to a switching circuit that switches high-frequency signals, and is particularly applicable to televisions. The signal switching circuit of the high frequency amplification stage in the tuner of a John receiver, or the satellite broadcasting circuit. A switch used in the signal switching circuit of the high frequency amplification stage and intermediate frequency amplification stage of the tuner. This relates to switching circuits.

0002

[Conventional technology]

Receivers that receive weak radio waves at high frequencies, such as satellite broadcasting receivers in recent years. The development of communication devices is actively underway. Figure 3 shows the high frequency amplification stage of such equipment. This is a conventional switching circuit used in an inter-frequency amplification stage.

0003 In FIG. 3, D1 to D8 are switching diodes consisting of Pin diodes. , C1-C3 and C6-C8 are DC cut capacitors, C4-C5, C9-C 10 and C13 are bypass capacitors, C12 is the emitter of the transistor amplifier This is a grounding capacitor. These capacitors have sufficiently low input voltage for high frequency signals. impedance.

0004 Also, R1 to R6 are bias resistors for switching diodes D1 to D8, and Q1 is a transistor for high frequency signal amplification, and R7 to R9 are vias of the above transistor Q1. The input matching circuit and the output matching circuit of the transistor Q1 are shown in the dotted line frame, respectively. Power matching circuit, , is the signal input terminal for input signals A and B, and the dotted line frame is the switching Drive circuit for diodes D1 to D8, is the signal input control terminal, is the signal output terminal child is the current terminal.

[0005] Now, if we set the signal input control terminal to GND potential and select the circuit on the input signal B side, , transistor Q3 of the drive circuit turns off, transistor Q2 turns on, and the drive circuit turns off. Switching diodes D1, D2, D7, D8 are off, switching diodes D3, D4, D5, and D6 are turned on. Therefore, the input signal A input from the signal input terminal is a switching diode. It is cut off by D1 and D2, DC cut capacitor C2, and switching diode. G via D3, DC cut capacitor C3, and switching diode D4. Since it is connected to ND, the input signal A is greatly attenuated.

[0006] On the other hand, the input signal B input from the signal input terminal is connected to the switching diode D5. ～Amplified by transistor Q1 and output to the signal terminal without being attenuated by D8 Powered.

[0007] Next, set the signal input control terminal to Vc potential and select the input signal A side circuit. Transistor Q3 of the live circuit is on, transistor Q2 is off, and the switch Switching diodes D1, D2, D7, D8 are on, switching diode D 3, D4, D5, and D6 are turned off. Therefore, the input signal A input from the signal input terminal is a switching diode. The signal is amplified by transistor Q1 and output without being attenuated by D1 to D4. output to the power terminal.

[0008] On the other hand, the input signal B input from the signal input terminal is connected to the switching diode D5. , D6, DC cut capacitor C7, switching diode D7 and GND via DC cut capacitor C8 and switching diode D8. It is greatly attenuated because it is connected to the Input signal switching is performed in the manner described above.

[0009]

[Problem that the idea aims to solve]

In the conventional circuit described above, sufficient isolation between input terminals is required. Since it is necessary to increase the number of switching diode elements to The disadvantage is that the signal loss increases when conduction occurs. Therefore, the input of a tuner that handles very weak signals, such as a tuner for receiving satellite broadcasting, To be used in a power switching circuit, the loss when on is large and the NF of the entire tuner is poor. There is a problem that it causes Also, if the number of switching diode elements is large, the bias circuit becomes complicated and expensive. There is also the problem of

0010

[Means to solve the problem]

The switching circuit according to the present invention has an emitter connection with a current feedback bias circuit. A switch is installed on the base side of a transistor high frequency amplifier consisting of ground high frequency transistors. A switching diode is provided as a bleeder for the base bias of the above high frequency transistor. The resistor and the bias resistor of the above switching diode are shared, and the above bleeder resistor is used. A drive circuit is provided to control the power supply of the resistor, and the drive circuit controls the above-mentioned switch. The base bias of the high frequency transistor and the high frequency transistor are controlled simultaneously. to be accomplished.

[0011] In addition, the power supply for the bleeder resistor is controlled in the drive circuit, and the high frequency By adding a function to simultaneously control the collector bias of wave transistors, The bias of the switching diode and the base bias and core of the high frequency transistor mentioned above. Create a configuration that controls the rectifier bias at the same time.

0012

[Effect]

According to the above configuration, the control voltage that turns on the switching circuit from the drive circuit When this occurs, the switching diode and high frequency transistor are connected via the bleeder resistor. A bias is applied that simultaneously turns on the input signal, and It leads to a high frequency transistor through a switching diode, and the transistor Amplify it and derive it from the output terminal.

[0013] When a control voltage is generated from the above drive circuit to turn off the switching circuit, The switching diode and high frequency transistor are turned off simultaneously through the A bias is applied to keep the circuit in the cutoff state.

[0014]

【Example】

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the same figure, C21 and C22 are capacitors for the input matching circuit, L21 and L2 2 is the inductance for the input matching circuit, and D21 and D22 are from the Pin diode. The switching diodes, Q21 and Q22 are high frequency transistors for high frequency amplification. The stars, R21 and R23 are for biasing the switching diodes D21 and D22. Resistors, R22 and R24 are for base bias of high frequency transistors Q21 and Q22. R25 and R26 are the emitter resistances of high frequency transistors Q21 and Q22, C25 and C26 are capacitors for grounding the emitters of high frequency transistors Q21 and Q22. C23, C24, C27, C28 are bypass capacitors, C29, C30 is a capacitor for output matching, and L23 and L24 are inductances for output matching. 10 consists of transistors Q23, Q24 and resistors R27, R28, R29. This is a drive circuit for switching elements.

[0015] When the voltage Vcc is applied to the control terminal SW of the drive circuit 10, the input A side is selected. Since the transistor Q23 is turned on by applying the voltage Vcc, Transistor Q24 turns off, switching diode D22 on the input B side and The base bias of the high-frequency transistor Q22 is turned off and the high-frequency transistor Q22 enters a cutoff state. Also, the bias of the switching diode D21 and the high frequency transistor Q21 A voltage Vcc is applied to the base bias from the control terminal SW of the drive circuit 10. Then, the switching diode D21 is turned on. Also, high frequency transistor Q2 1 operates as a high frequency amplification element.

[0016] Therefore, the signal from the input A side is transferred to the switching diode with almost no attenuation. It passes through the code D21, is amplified by the high frequency transistor Q21, and is output from the output terminal. derived. Conversely, the signal from the input B side is the switching diode D22, high frequency It is greatly attenuated by transistor Q22.

[0017] Next, when the control terminal SW of the drive circuit 10 is connected to GND, the input B side is selected. selected. When control terminal SW is connected to GND, switching diode D21 and The base bias of the high-frequency transistor Q21 is turned off, and the signal from the input A side is is greatly attenuated. Conversely, the signal on the input B side passes through the switching diode D2 with almost no attenuation. 2, is amplified by the high frequency transistor Q22, and is led out to the output terminal. Ru.

[0018] FIG. 2 is a circuit diagram of another embodiment of the present invention, and parts corresponding to FIG. 1 are designated by the same reference numerals. The attached explanation will be omitted. The difference between the switching circuit in Figure 2 and the circuit in Figure 1 is that the base bias Connect the power supply side of resistors R22, R24 and inductances L23, L24 for output matching. They are commonly connected to the control terminal SW of the drive circuit 10 and the transistor Q24. Connected to the emitter, bias of switching diodes D21 and D22 and high frequency While simultaneously controlling the base bias of transistors Q21 and Q22, The collector bias of transistors Q21 and Q22 is also controlled at the same time. Is Rukoto. Since the operation is substantially the same as that of the embodiment shown in FIG. 1, the explanation thereof will be omitted. .

[0019]

[Effect of the idea]

Since the present invention has the above configuration, the number of elements in the switching circuit can be significantly reduced. A switch with low passing loss when weak signals pass through the circuit. To provide an input switching circuit with less deterioration of NF of the circuit since a switching circuit can be realized. be able to. In addition, the bias circuit can be simplified, resulting in a stable and inexpensive switch. A switching circuit can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of another embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional example.

[Explanation of symbols]

Q21, Q22 High frequency transistor D21, D22 switching diode R22, R24 Base bias resistor 10 Drive circuit

Claims (2)

[Scope of utility model registration request] Claim 1: A switching diode is provided on the base side of a transistor high frequency amplifier composed of a common emitter high frequency transistor having a current feedback bias circuit,
A drive circuit is provided which shares the base bias bleeder resistor of the high frequency transistor and the bias resistor of the switching diode and controls the power supply of the bleeder resistor, and the drive circuit simultaneously controls the base bias of the switching diode and the high frequency transistor. A switching circuit characterized in that: 2. A switching diode is provided on the base side of a transistor high frequency amplifier composed of a common emitter high frequency transistor having a current feedback bias circuit,
A drive circuit is provided that shares a base bias bleeder resistor of the high frequency transistor and a bias resistor of the switching diode, controls the power supply of the bleeder resistor, and simultaneously controls the collector bias of the high frequency transistor, and the drive circuit A switching circuit characterized in that the bias of the switching diode and the base bias and collector bias of the high frequency transistor are controlled simultaneously.