JPH05291920A - High frequency diode switch circuit - Google Patents

Abstract

PURPOSE:To enhance an isolation with a simple circuit and to eliminate a need for a negative power supply by providing a switching means turning on/off a power supply to a buffer amplifier and giving a forward bias to a diode to the switch circuit. CONSTITUTION:A voltage equal to a power supply voltage is applied to an anode of a diode 9 attended with the turning on of a switching transistor(TR) 7. Moreover, when a control voltage fed to a base of the TR 7 is high, since the TR7 is turned on, a buffer amplifier 1 is turned off and an anode potential of the diode is lost, then a reverse bias is applied to diodes 9,10, which are turned off. As a result, a high frequency signal inputted to the amplifier 1 is interrupted by the amplifier 1 and the diode and no output appears at an output terminal 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency diode switch circuit, and more particularly to a circuit used in a high frequency signal output circuit of communication equipment or the like and having improved isolation during ON-OFF.

[0002]

2. Description of the Related Art Conventionally, a switch circuit using a diode is sometimes used in a high frequency output stage of a radio transmitter or the like, for example, a coupling circuit between a transmission output amplifier and an antenna device. In this case, an expensive PIN diode is used to increase isolation (one-way) when the switch is turned on, that is, non-conductivity when the switch is turned off, and to reduce switch insertion loss when the switch is turned on. In order to increase the power consumption, it is necessary to connect a plurality of PIN diodes in series, which inevitably becomes expensive.

Further, since it is necessary to apply a reverse bias voltage to the diode when the switch is turned off, a negative power source must be provided, and there is a drawback that a plurality of device circuits are required.

[0004]

An object of the present invention is to eliminate the drawbacks of the conventional high frequency diode switch, and the isolation is improved by a simple circuit, and the circuit is simplified by eliminating the negative power supply. An object is to provide a high frequency diode switch circuit.

[0005]

[Outline] To achieve the above object, the present invention turns on a buffer amplifier having a high input impedance, a diode connected to an output terminal thereof, and a power supply supplied to the buffer amplifier.
And a switching means that is turned off and applies a forward bias to the diode.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, 1 is a buffer amplifier using a transistor, and a high frequency signal to be controlled is applied to the base of the transistor 2 via a capacitor 3, and the base bias resistors 4 and 5 and the emitter output resistor 6 are provided. And are connected. Further, 7 is a PNP transistor, a power supply voltage is applied to its emitter, and a collector is connected to the base bias resistor 4 of the buffer amplifier 1 and the collector of the transistor 1 as a power supply output.

Further, two diodes 9 and 10 are connected in series to the output terminal of the buffer amplifier, that is, the emitter of the transistor 2 in this example, via a DC blocking capacitor 8, and the anode of the diode 9 has a resistor 11 connected thereto. Connected to the collector of the switching transistor 7 via
The cathode of the second diode 10 is connected to the power source via the resistor 12, and is further connected to the ground via the resistor 13, and the output terminal thereof is connected to the output terminal 15 via the DC blocking capacitor 14. A limiting signal is applied to the base of the switching transistor 7, and switch control of the circuit is performed by changing the control signal to a high potential or a low potential. The circuit constants in the above circuit are as shown in the figure.

The circuit configured as described above operates as follows. First, when the voltage applied to the base of the switching transistor 7 has a low potential, an emitter current flows, so that the transistor is turned on, and a high potential is applied to the buffer amplifier and the anode of the diode 9 via the collector thereof. Although the operation of the buffer amplifier is the same as that of the conventional amplifier, the description thereof is omitted. However, since the amplifier is an emitter follower type, the input impedance seen from the base is extremely high, and the emitter has a moderate amplification degree. No, but the output of the amplifier appears.

Further, the O of the switching transistor 7 is
Along with N, a voltage substantially equal to the power supply voltage (strictly speaking, a voltage drop between the emitter and collector of the switching transistor is included, but ignored here) is applied.

On the other hand, the power supply voltage is applied to the cathode of the second diode 10 after being divided by the resistors 12 and 13, but since the voltage of this portion is lower than the voltage of the anode, the diode is normally forwarded. A bias is applied in the direction and it becomes conductive. Therefore, the output of the buffer amplifier is the output terminal 15
Is supplied to the next-stage circuit or device (not shown).

When the control voltage applied to the base of the switching transistor 7 has a high potential, the transistor 7 is turned off, so that the buffer amplifier is turned off.
At the same time, the potential on the anode side of the diode disappears, so that a reverse bias is applied to the diodes 9 and 10 to turn them off. As a result, the high frequency signal input to the buffer amplifier 1 is blocked by both the buffer amplifier and the diode, and no output appears at the output terminal 15.

As described above, according to the second circuit, both the buffer amplifier and the diode are turned off in the OFF state of the switch operation, and a reverse bias voltage is applied to the diode, so that the capacitance between the terminals of the diode itself. Is extremely small, so that larger isolation can be obtained in addition to the isolation of the buffer amplifier.

The resistor 12 inserted between the cathode of the diode and the power supply is for applying a reverse bias voltage when the diode is OFF.
It can be put to practical use if not so much isolation is required. Further, the circuit of each part is not limited to the above-mentioned embodiment, and various modifications can be made. It should be noted that if a PIN diode is used as the diode as in the conventional case, higher performance can be achieved, but the number of used diodes is smaller than in the conventional case, which is economical.

[0014]

Since the present invention is constructed and operates as described above, it is possible to realize a switch circuit having a large isolation with a simple circuit, and a negative power supply is not required. It is also effective in realizing simplification of the circuit.

[Brief description of drawings]

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

[Explanation of symbols]

1 ... Buffer amplifier, 2 ... Transistor, 3, 8,
14 ... Capacitors 4, 5, 6, 11, 12, 13 ... Resistors, 7 ... Switching transistors, 9, 10 ... Diodes, 15 ... Output terminals

Claims (1)

[Claims] 1. A buffer amplifier having a high input impedance, a diode connected to an output end of the buffer amplifier, and a switching means for turning on / off a power supply to the buffer amplifier and applying a forward bias to the diode. Characteristic high frequency diode switch circuit.