JPH09130208A - Electronic attenuation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evade the degradation of attenuation characteristics and to lower the current consumption of a circuit. SOLUTION: A capacitor 14 passes through radio signals from an antenna 1, the capacitor 22 outputs attenuated radio signals to an output terminal 23 and Schottky diodes 12 and 13 attenuate the radio signals. A transistor 24 imparts the voltage of a power source 20 to the Schottky diode 13 as a DC bias voltage by the control of BS signals 8, the transistor 18 is turned on/off by control signals 3 and decides the value of a DC bias current set in a resistor 16 or the resistor 17 and the capacitor 15 cancels the inter-terminal capacitance of the Schottky diodes 12 and 13. The resistors 19 and 25 limit the base current of the transistor and the resistor 21 is turned to a reverse bias resistor when the transistor 24 is turned off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic attenuating circuit, and more particularly to an electronic attenuating circuit for attenuating a radio signal input from an antenna by switching a bias resistance of a Schottky diode.

[0002]

2. Description of the Related Art Conventionally, PIN diodes have been used in this kind of attenuation circuit.

As an example of an attenuator circuit using such a PIN diode, an "electronic attenuator" described in JP-A-60-112306 is known.

In this publication, three PIN diodes are inserted in a π-type circuit between a input terminal and an output terminal via a DC blocking capacitor, and attenuation control is performed by applying a bias from a drive circuit to the diodes. Has been done.

However, since the PIN diode has a high forward voltage, the PIN diode cannot be expected to be sufficiently driven by a voltage of about 1.5 V generated by one normal battery.

Therefore, in applying the forward bias, it takes 2
It may not be possible to drive them sufficiently in series, and as a result, a Schottky diode having a low forward voltage may be used as an alternative.

Here, the Schottky diode is a diode that utilizes the rectification characteristics of a potential barrier called a Schottky barrier formed at the contact interface between a metal and a semiconductor. Since the injection of carriers is extremely small, it has a feature that the rectification characteristics are not deteriorated even in a high frequency region.

FIG. 3 is a block diagram showing a conventional electronic attenuation circuit.

Referring to FIG. 3, the conventional electronic attenuating circuit includes an antenna 1, a capacitor 14 for passing a radio signal from an input terminal 11, a Schottky diode 13 connected in series for performing radio wave attenuation control, and 12
A transistor 24 for applying a DC bias voltage of the power supply 20 to the Schottky diode 13, a resistor 25 connected to the base of the transistor 24 for controlling conduction of the transistor by the BS signal 8, and a collector and a ground point of the transistor 24. A resistor 21 connected between them, a resistor 26 for setting the bias current of the Schottky diodes 13 and 12 by the control signal 3, a bypass capacitor 15, and a capacitor 22 for passing the attenuated radio signal to the output terminal 23. It consists of

Next, the operation will be described.

The radio signal received by the antenna 1 is input to the input terminal 11. The radio signal is applied to the Schottky diode 13 and the Schottky diode 12 via the capacitor 14. Schottky diode 1
3 and 12 are I depending on the applied DC bias voltage.
Receives the amount of attenuation due to F-RS.

Here, IF is the Schottky diode 1
3 represents a forward current flowing through the transistors 3 and 12, and RS is a resistance between terminals of the Schottky diodes 13 and 12 determined by the forward current IF. Since the cathode of the Schottky diode 12 is grounded at a high frequency by the bypass capacitor 15, the radio signal applied to the anode of the Schottky diode 12 is attenuated by the terminal resistance RS of the Schottky diode 12. .

The attenuated radio signal is output to the output terminal 23 through the capacitor 22.

Here, the amount of attenuation of the radio signal is controlled by the reverse bias resistor 26 connected to the cathode of the Schottky diode 12 and the voltage of the control signal 3.

That is, the attenuation amount is controlled by adding the resistor 26 having a resistance value to the high frequency grounding by the capacitor 15. Also, Schottky diode 1
The forward bias current through 3 and 12 is set by resistor 26.

In this case, since the reverse leakage current of the Schottky diodes 13 and 12 is determined only by the characteristics of the resistor 26 and the Schottky diodes 13 and 12 and the resistor 21, the value of the resistor 26 is increased to increase the leakage current. On the other hand, if it is tried to suppress, the amount of attenuation cannot be sufficiently obtained.

On the other hand, the application of the DC bias voltage to the Schottky diodes 13 and 12 is performed by the conduction cutoff operation of the transistor 24, and this operation is controlled by the BS signal 8 applied via the resistor 25.

When the voltage of the BS signal 8 is lower than the voltage of the power supply 20, the transistor 24 becomes conductive, so that the power supply 20
The voltage is applied to the Schottky diodes 13 and 12 in the forward bias voltage and attenuation control is performed. Also, B
When the voltage of the S signal 8 is higher than the voltage of the power supply 20, the transistor 24 is cut off, so that the ground potential gives a reverse bias voltage to the Schottky diodes 13 and 12 via the resistor 21. In this case, damping control is not performed.

The Schottky diode has a large leak current in the reverse direction as a general characteristic, so that the current consumption of the circuit becomes large. If the attenuation control is not performed, the value of the resistor 26 is increased in order to suppress this leak current.
Since it also doubles as the setting of the forward bias current of 2, the increase of the resistance value suppresses the forward bias current of about 1 mA at which the desired attenuation can be obtained.

Therefore, if the resistance value is excessively increased to suppress the leak current, the attenuation amount is lowered and the attenuation characteristic is deteriorated.

As another method of suppressing the leak current, it is possible to select and use a Schottky diode having a small leak current, but in addition to the problem of workability, generally, satisfactory characteristics are rarely obtained.

[0022]

The conventional electronic attenuation circuit described above has a large reverse leakage current as a general characteristic of a Schottky diode, so that the current consumption of the circuit in the state where the attenuation operation is not performed is large. Has the drawback of being large.

Further, if the value of the reverse bias resistance is increased in order to suppress the reverse leakage current, there is a drawback that the attenuation characteristic is deteriorated.

An object of the present invention is to provide an electronic attenuating circuit that consumes a small amount of current in a state where the attenuating operation is not performed and does not deteriorate the attenuating characteristic.

[0025]

The electronic attenuating circuit of the present invention comprises a line for passing a radio signal from an antenna input terminal to an output terminal; and a series connection point of first and second diodes connected to the line. A diode array; the first
A bias means for applying a DC bias to the other end of the diode; and a resistor connected to the other end of the second diode; in the electronic attenuation circuit, the resistor is constituted by resistance switching means. I am trying.

Also, a first capacitor that allows the wireless signal from the antenna input terminal to pass therethrough; and a second capacitor that is connected in series with this and outputs the wireless signal to the output terminal;
A first Schottky diode having a cathode connected to the connection point of the first and second capacitors; a second Schottky diode having an anode connected to the connection point; an anode of the first Schottky diode A direct current bias circuit for providing a direct current bias current by a first control signal; a third capacitor connected between the cathode of the second Schottky diode and a ground point; and a cathode of the second Schottky diode A resistance switching means for switching the first resistance by the second control signal, in an electronic attenuation circuit comprising: a first resistance connected to and setting the value of the DC bias current by a second control signal. It is characterized by being configured with.

The resistance switching means includes a transistor;
A second resistor connected to the base of the transistor; a third resistor connected to the other end of the second resistor and the emitter of the transistor and connected to the cathode of the second Schottky diode; And a fourth resistor connected between the collector and the ground point.

Further, the resistance switching means is constituted by a voltage variable resistance element.

[0029]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the electronic attenuation circuit of the present invention.

The present embodiment shown in FIG. 1 has an antenna 1
A capacitor 14 for passing a radio signal from the input terminal 11, Schottky diodes 13 and 12 connected in series for controlling attenuation of the radio signal, and a transistor for applying a DC bias voltage of the power supply 20 to the Schottky diode 13. 24, a resistor 25 connected to the base of the transistor 24 to control conduction of the transistor by the BS signal 8, a resistor 21 connected to the collector of the transistor 24 and the ground point, and a Schottky diode 13.
And resistance switching circuit 1 for setting bias conditions of 12
0, a bypass capacitor 15, and a capacitor 22 that passes the attenuated radio signal to the output terminal 23.

The resistance switching circuit 10 includes a resistance 17 for forward bias, a resistance 16 for reverse bias, and a transistor 18 for switching these resistances by a control signal 3.
And a resistor 19 for limiting current.

In FIG. 1, components corresponding to those shown in FIG. 3 are designated by the same reference numerals or symbols, and their description will be omitted.

Next, the operation of this embodiment will be described in more detail with reference to FIG.

The bias currents of the Schottky diodes 13 and 12 are determined by the resistance 16 for reverse bias and the resistance 17 for forward bias.

Switching between the reverse biasing resistor 16 and the forward biasing resistor 17 is performed by the conduction / interruption operation of the transistor 18, and this operation is performed by the transistor biasing resistor 19 and the control signal 3.

On the other hand, application of the DC bias voltage to the Schottky diode 13 is performed by cutting off the conduction of the transistor 24, and is controlled by the BS signal 8 applied via the resistor 25.

When the voltage of the BS signal 8 is lower than the voltage of the power supply 20, the transistor 24 becomes conductive, so that the power supply 20
Applies a forward bias voltage to Schottky diodes 13 and 12. Further, when the voltage of the BS signal 8 is higher than the voltage of the power supply 20, the transistor 24 is cut off, so that the ground potential gives the reverse bias voltage to the Schottky diodes 13 and 12 via the resistor 21.

When the voltage of the control signal 3 is smaller than the emitter voltage of the transistor 18 while the transistor 24 is conductive, the emitter-collector of the transistor 18 is conductive and the Schottky diodes 13 and 12 are in the order determined by the resistor 17. Since the directional bias current flows, the radio signal is attenuated.

Further, when the voltage of the control signal 3 is higher than the emitter voltage of the transistor 18 in the state where the transistor 24 is cut off, the emitter-collector of the transistor 18 is cut off so that no current flows through the resistor 17 and the resistor 21.
And Schottky diodes 13 and 12 have a resistor 16
A reverse bias current will flow through. In this case, the radio signal is not attenuated.

Since the resistor 16 is used for the purpose of applying a reverse bias voltage to the Schottky diodes 13 and 12, it is not necessary to pass a large current, and therefore the resistance value is set high.

As described above, when the radio signal is attenuated, the forward bias current of the Schottky diodes 13 and 12 is caused by the resistor 17, and when the radio signal is not attenuated, the Schottky diode 13 and the Schottky diode 13 are caused by the resistor 16. Twelve reverse bias currents are set independently.

In place of the resistance switching circuit 10 for the resistors 16 and 17 formed by the transistor 18, for example, a voltage variable element using a field effect transistor in which the resistance value between the drain and the source changes depending on the voltage value of the control signal 3 is used. It is also possible to do so.

FIG. 2 is a block diagram showing an example in which the electronic attenuation circuit of FIG. 1 is incorporated in a device.

Referring to FIG. 2, the radio signal received by the antenna 1 is input to the attenuation circuit 2. The input radio signal is selected to be attenuated or not attenuated by the control signal 3 output from the decoder 6.

The radio signal output from the attenuation circuit 2 is input to the reception circuit 4 and is amplified and demodulated. The demodulated signal is
It is input to the waveform shaping circuit 5 and converted into a digital signal that can be read by the decoder 6.

The decoder 6 compares the data signal 9 output from the waveform shaping circuit 5 with its own selective calling signal 26 previously recorded in the programmable read only memory (PROM) 7, and attenuates when they match. The circuit 2 does not attenuate the radio signal, and if they do not match, the attenuation circuit 2 outputs the control signal 3 that attenuates the radio signal.

Further, the decoder 6 outputs a BS signal 8 for operating the receiving circuit 4 intermittently for the purpose of low current consumption. The BS signal 8 is input to the receiving circuit 4 and the BS signal 8
The ON / OFF control of the power supply of the receiving circuit 4 is performed in this state. That is, the transistor 24 of FIG. 1 is turned off.

[0049]

As described above, in the electronic attenuating circuit of the present invention, the resistors that determine the forward bias current and the reverse bias current of the Schottky diode are independent, so that the reverse bias current of the Schottky diode is reduced. A high resistance that can limit the leakage current is used, and the resistance value of the forward bias current, which causes the problem of attenuation, can be reduced, so there is no performance deterioration due to the reverse current, the range of selectable Schottky diodes is widened, and the This has the effect of ensuring the amount of attenuation.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing an example in which the electronic attenuation circuit of FIG. 1 is incorporated in a device.

FIG. 3 is a block diagram showing a conventional electronic attenuation circuit.

[Explanation of symbols]

 1 Antenna 2 Attenuation Circuit 3 Control Signal 4 Reception Circuit 5 Waveform Shaping Circuit 6 Decoder 7 Programmable Read Only Memory 8 BS Signal 9 Data Signal 10 Resistance Switching Circuit 11 Input Terminal 12, 13 Schottky Diode 14, 15 Capacitor 16, 17 Resistance 18 Transistor 19 Resistor 20 Power supply 21 Resistor 22 Capacitor 23 Output terminal 24 Transistor 25 Resistor 26 Selective call signal

Claims (4)

[Claims] 1. A line for passing a radio signal from an antenna input terminal to an output terminal; a diode string in which a series connection point of first and second diodes is connected to the line; and another line of the first diode. An electronic attenuating circuit comprising: biasing means for applying a DC bias to one end; and a resistor connected to the other end of the second diode, wherein the resistor is constituted by a resistance switching means. . 2. A first capacitor that allows a radio signal from an antenna input terminal to pass therethrough; a second capacitor that is connected in series with the radio signal and outputs the radio signal to an output terminal; the first and second capacitors A first Schottky diode having a cathode connected to a connection point; a second Schottky diode having an anode connected to the connection point; and a first direct current bias current control to the anode of the first Schottky diode. A DC bias circuit provided by a signal; a third capacitor connected between the cathode of the second Schottky diode and a ground point; the second
Which is connected to the cathode of the Schottky diode, and sets the value of the DC bias current by the second control signal.
An electronic attenuating circuit comprising: a resistance switching means for switching the first resistance according to the second control signal. 3. The resistance switching means includes: a transistor; a second resistor connected to the base of the transistor; another end of the second resistor and the emitter of the transistor, and the second Schottky. 3. An electron according to claim 1 or 2, comprising a third resistor connected to the cathode of the diode; and a fourth resistor connected between the collector of the transistor and the ground point. Attenuation circuit. 4. The resistance switching means is composed of a voltage variable resistance element.
Electronic damping circuit as described.