JP2000031744A - Modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the modulation index of a modulator that is easily made into an integrated circuit. SOLUTION: A modulation wave S2 is applied to a drain of a field effect transistor(FET) 12 via a modulation wave input means 13 and fed to a drain of a FET 22 via a modulator wave input means 23. A carrier S1 is fed to a gate of the FET 12 via a carrier input means 11. The FET 12 amplifies the carrier S1 and outputs it to its drain. In the case that a voltage of the modulation wave S2 is low, the component of the carrier S1 in the amplified signal is sufficiently lowered. The result of amplification is linearly amplifier by the FET 22 and the amplified output of the FET 22 is outputted to the drain of the FET 22 as a modulated wave Vout and it is outputted via a modulated wave output terminal Out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is at the core of an expressway traffic system (hereinafter referred to as "ITS") related to intelligence between a road and a traffic tool such as a car which is attracting attention as a new industrial field. In a non-stop automatic toll collection system (hereinafter referred to as "ETC"), an MMIC (Monolithic Microwave Integrated Circ)
uit).

[0002]

2. Description of the Related Art Conventionally, techniques in such a field include:
For example, there is one described in the following literature. Reference: Transistor Technology Editor "Practical Electronic Circuit Handbook" (1997) CQ Publishing Company, p. 228 FIG. 2 is a schematic circuit diagram showing a conventional modulator described in the above-mentioned reference. The modulator includes a carrier input section 1 composed of a split transformer for inputting a carrier S1, a bipolar transistor 2 for amplification, and a modulated wave input section 3 formed of a split transformer for inputting a modulated wave S2. And a modulated wave output section 4 comprising a separate type transformer for outputting the modulated wave Vout. In the modulator having such a configuration, the carrier wave S1 is input from the carrier wave input unit 1 and is provided to the base of the bipolar transistor 2 to be amplified by the bipolar transistor 2. On the other hand, the modulated wave S2 is input from the modulated wave input unit 3, and is output from the bipolar transistor 2
The level of the carrier wave S1 amplified by the bipolar transistor 2 is controlled by the modulated wave S2. As a result, the carrier wave S1 is modulated by the modulation wave S2, and a modulated wave Vout is generated. The generated modulated wave Vout is output from the modulated wave output unit 4.

[0003]

However, the conventional modulator shown in FIG. 2 has the following problems. In the modulator of FIG. 2, a carrier input unit 1 composed of a separate type transformer is used.
And a separated bipolar transistor 2, a modulated wave input unit 3 formed of a separated transformer, and a modulated wave output unit 4 formed of a separated transformer.
Therefore, there is a problem that not only the size of the circuit is increased but also the production cost is increased. In order to overcome such a problem, for example, a carrier wave S1 is directly input to a gate, the carrier wave S1 is amplified, and a field effect transistor (hereinafter referred to as an FET) is output from a drain. A modulator that generates and outputs a modulated wave Vout by directly applying the voltage to the drain to control the drain voltage of the FET may be considered.

In the modulator having such a configuration, the FET amplifies the carrier wave S1 and outputs the amplified signal from the drain, which is modulated by the modulated wave S2 and output to the load as the modulated wave Vout. Here, when the modulation wave S1 is at the maximum, the FET is saturated due to the settings of the load and the bias. When the modulated wave S1 becomes small, the operating point approaches the origin, and the FET drain Id
s and the drain-source voltage Vds decrease. Therefore, the modulated wave Vout modulated in the saturated state with an output proportional to the magnitude of the modulated wave S2 is obtained. Regarding the relationship between the magnitude of the modulated wave Vout and the modulated wave S2, a linear characteristic is obtained in a large range and a large signal. And the modulator which can be easily made into MMIC can be realized. However, the modulator which can be easily converted to the MMIC still has the following problems to be solved.

FIG. 3 is a diagram showing simulation data of a modulation characteristic and a modulation index in a conventional modulator which can be easily converted to an MMIC. The horizontal axis represents the voltage of the modulated wave S2, and the vertical axis represents the modulated wave Vout. 2 shows an envelope voltage. MMI
In the conventional modulator which can be easily converted to C, when the modulated wave S2 is small or zero, the amplitude of the modulated wave Vout becomes small, but still remains to some extent. Therefore, the ratio between the maximum amplitude and the minimum amplitude of the modulated wave Vout becomes 825/45 = 18 times, for example, as shown in FIG. In this case, the modulation index K defined by (maximum amplitude−minimum amplitude) / (maximum amplitude + minimum amplitude) is 0.896.
And the actual measured value required by the ETC system etc. is 0.9
The above modulation index K may not be obtained. The present invention
It is an object of the present invention to solve the above-mentioned problems of the related art and to provide a modulator that can sufficiently obtain a modulation index K and is suitable for MMIC.

[0006]

Means for Solving the Problems In order to solve the above problems, a first invention of the present invention has the following configuration in a modulator. That is, a first modulation circuit that modulates a carrier with a modulation wave, and a second modulation circuit that further modulates the carrier modulated by the first modulation circuit with the modulation wave to generate a modulated wave. Make up. By employing such a configuration, the modulated wave modulates the carrier wave in two stages to generate the modulated wave, so that the amplitude of the modulated wave when the level of the modulated wave is low is sufficiently small.

In a second aspect, the first aspect of the first aspect is provided.
And the second modulation circuit are configured as follows. That is, the first modulation circuit includes a carrier input unit that transmits the carrier input from the first input terminal without altering the carrier, a first conductive electrode, a second conductive electrode, and the carrier input. A first transistor connected to control a conduction state between the first and second conduction electrodes, and a first transistor for amplifying the carrier wave and outputting the amplified carrier wave to the first conduction electrode; And transmitting the modulated wave input from the second input terminal to the first conductive electrode of the first transistor without alteration, and modulating the carrier wave amplified by the first transistor with the modulated wave. And one modulated wave input means. The second modulation circuit is connected to a third conductive electrode, a fourth conductive electrode, and a first conductive electrode of the first transistor, and controls a conductive state between the third and fourth conductive electrodes. A second transistor having a second control electrode for amplifying the modulated carrier and outputting the amplified carrier to the third conductive electrode; and modulating the modulated wave input from the second input terminal. A second modulated wave input means for generating the modulated wave by further modulating the carrier wave modulated by the modulated wave by applying the modulated wave to the third conductive electrode of the second transistor without generating the modulated wave. And modulated wave output means for transmitting the modulated wave to an output terminal without altering the modulated wave. By adopting such a configuration, the carrier wave and the modulated wave are directly transmitted to the first control electrode of the first transistor and the first control electrode without using a transformer that is not suitable for MMIC such as a separation type transformer. A conductive electrode, and a third conductive electrode of the second transistor. The first and second transistors allow the carrier wave to be 2
A modulated wave is generated by being modulated in stages, and the amplitude of the modulated wave when the level of the modulated wave is low becomes sufficiently small.

According to a third aspect, in the modulator according to the second aspect, the following configuration is provided. That is, the first and second transistors are composed of GaAs FETs formed on a common GaAs (gallium arsenide) substrate, and the carrier wave input means, the first modulation wave input means, and the second modulation wave input means The means and the modulated wave output means are constituted by passive elements formed on the common gallium arsenide substrate. By employing such a configuration, the first modulation circuit and the second modulation circuit are formed on a GaAs substrate having excellent common high-frequency characteristics, and are formed into MMICs. According to a fourth aspect, in the modulator according to the second or third aspect, the following third transistor is provided. The third transistor is connected to a fifth conductive electrode connected to a power supply, a sixth conductive electrode connected to the first and second modulated wave input means, and to the second input terminal. A third control electrode for controlling a conductive state between the fifth and sixth conductive electrodes, wherein the modulated wave is supplied to the third control electrode from the second input terminal, Is supplied to the first and second modulated wave input means. By adopting such a configuration, the first and second modulated wave inputs are applied to the first conductive electrode of the first transistor and the third conductive electrode of the second transistor instead of the modulated wave. Through the means, a signal obtained by driving the modulated wave with the power supply by the third transistor is provided.

According to a fifth aspect of the present invention, in the modulator according to the fourth aspect, the third transistor is connected to the common GaAs.
It is composed of a GaAs FET formed on a substrate. By adopting such a configuration, the third transistor is also formed on the GaAs substrate and formed into an MMIC. Also,
Instead of providing the modulated wave to the first and third conductive electrodes of the first and second transistors, a signal for driving the modulated wave is provided.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a schematic circuit diagram of a modulator showing a first embodiment of the present invention. This modulator includes a first modulation circuit 10 in a first stage and a second modulation circuit 20 in a subsequent stage formed on a common GaAs substrate, and is MMIC. The modulation circuit 10 has a first input terminal In1 for inputting the carrier S1.
, An MES-type GaAs FET 12 for inputting a carrier S1 via the carrier input 11 to a gate serving as a first control electrode, and a modulated wave S
2, a modulated wave input means 13 connected to a second input terminal In2 for inputting the second GaAs FET 12 and the GaAsF 12 connected between a source, which is a second conductive electrode of the GaAs FET 12, and ground.
And a self-biasing circuit 14 for the ET 12. The carrier input means 11 is a means for transmitting the carrier S1,
A capacitor 1 having one electrode connected to the input terminal In1 and the other electrode connected to the gate of the GaAs FET 12
1a and a resistor 11b connected between the gate of the GaAs FET 12 and the connection point of the capacitor 11a and the ground. The modulating wave input means 13 is a means for transmitting the modulating wave S2 and constitutes a load of the GaAs FET 12. The modulating wave input means 13 has a resistor 13a having one end connected to the input terminal In2, the other end of the resistor 13a and the GaAs FET
And an inductor 13b connected between the drain of the twelfth first conductive electrode. Self bias circuit 14
Has a resistor 14a for connecting the source of the GaAs FET 12 to the ground in a DC manner, and a capacitor 14b for connecting the source of the GaAs FET 12 to the ground in an AC manner.

On the other hand, the modulation circuit 20 includes the GaAsFE
An input circuit 21 for inputting a signal supplied from the drain of T12, a GaAs FET 22 having a gate connected to the input circuit 21, and an input terminal I
A second modulated wave input means 23 connected to n2, a self-bias circuit 24, and a modulated wave output means 25 are provided. The input circuit 21 is composed of GaAs in the first modulation circuit 10.
A capacitor 21a having one electrode connected to the drain of the FET 12 and the other electrode connected to the gate, which is the second control electrode of the GaAs FET 22, and a connection point between the other electrode of the capacitor 21a and the gate of the GaAs FET 22; And a resistor 21b connected between the two. The modulation wave input means 23 is a means for transmitting the modulation wave S2 to the GaAs FET 22, and has one end connected to the input terminal In2 and a capacitor 23a having one electrode connected to the input terminal In2 and the other electrode grounded. ,
The other end has an inductor 23 b connected to the drain, which is the third conductive electrode of the GaAs FET 22. The self-bias circuit 24 includes a resistor 24 for connecting the source, which is the fourth conductive electrode of the GaAs FET 22, to the ground in a DC manner.
a, and a capacitor 24b for connecting the source of the GaAs FET 22 to the ground in an AC manner. The zero-harmonic output means 25 has a capacitor 25a connected between the drain of the GaAs FET 22 and the output terminal Out.

Next, the operation of the modulator shown in FIG. 1 will be described. The modulated wave S2 is supplied to the GaAsFE through the modulated wave input means 13.
The voltage is applied to the drain of T12 and to the drain of the GaAs FET 22 via the modulated wave input means 23. The carrier S1 is GaAs via the carrier input means 11.
Applied to the gate of sFET12. GaAs FET1
2 amplifies the carrier wave S1 based on the applied modulated wave S1 and outputs it to the drain. FIG. 4 shows the GaAs in FIG.
FIG. 4 is a characteristic diagram showing a DC characteristic and a load line of the FET 12. FIG. 4 is a simulation result using MDS (Microwave Design System), in which the carrier S1 is 5.8 KHz. When the level of the modulated wave S2 is low, even if the carrier wave S1 is the same, the load line also moves to the origin side as shown in FIG. 4 because the drain voltage moves as the level of the modulated wave S2 decreases. , The component of the carrier wave S1 in the amplification result of the GaAs FET 12 is also reduced. That is, in the modulation circuit 10, a modulated wave having a considerably small amplitude can be obtained from the small signal modulated wave S2. Modulation circuit 1
The amplification result output from 0 is applied to the gate of the GaAs FET 22 in the modulation circuit 20 via the input circuit 21. The GaAs FET 22 is brought into a saturated state by the setting of the load and bias of the inductor 23b and the capacitor 25a, and the modulation circuit 10 provided through the input circuit 21
Is amplified over a large range to generate a modulated wave Vout and output it to the drain. In the amplification here, the modulated wave S
2 and becomes a modulated wave Vo that is linearly modulated.
ut is obtained.

As described above, in the first embodiment,
It has the following advantages. (1) Carrier wave input means 11, modulated wave input means 13, 2
3. The modulated wave output means 25 is GaAs
Since the carrier wave S1 and the modulated wave S2 are directly applied to the FETs 12 and 22, a transformer or the like is not required, and the MMI is not required.
C conversion is facilitated and cost can be reduced. (2) GaAs FET with modulation formed on GaAs substrate
Since modulation is performed in steps 12 and 22, modulation suitable for high frequencies can be performed. (3) FIG. 5 is a diagram showing the modulation characteristics and the modulation index of FIG. The carrier wave S1 is modulated by the modulation wave S2 in two stages of the modulation circuit 10 and the modulation circuit 20, and the modulation circuit 10 generates a modulated wave having a small amplitude of the component of the carrier wave S1. , It is modulated in a large range in a saturated state, so that not only a linear modulation characteristic in a large range and a large signal can be obtained, but also the modulated wave Vout
The ratio of the maximum amplitude to the minimum amplitude is, for example, as shown in FIG.
The modulation index K defined by (maximum amplitude−minimum amplitude) / (maximum amplitude + minimum amplitude) becomes 0.975,
A modulation index K of 0.9 or more can be sufficiently obtained by an actual measurement value required by an ETC system or the like.

Second Embodiment FIG. 6 is a schematic circuit diagram of a modulator according to a second embodiment of the present invention. The elements common to the elements in FIG. 1 according to the first embodiment are shown in FIG. Common symbols are assigned. In the first embodiment, the modulated wave S2 input from the input terminal In2 is transmitted through the modulated wave input means 13 and 23 to the GaAs FET 12,
In the second embodiment, the modulated wave S2 is supplied to the drains of the GaAs FETs 12 and 22.
, A driving signal S3 corresponding to the modulated wave S2 is generated, and the driving signal S3 is
ET12 and ET22, the input circuit 30 connected to the input terminal In2 and the third
GaAs FET 31 is provided.

The input circuit 30 has a resistor 30a connected between the input terminal In2 and the ground.
The modulation wave S2 is input to the gate as the third control electrode through the input circuit 30. GaAs
The drain, which is the fifth conductive electrode of the sFET 31, is connected to the power supply 32, and the source, which is the sixth conductive electrode of the GaAs FET 31, is connected via the inductor 33 to the resistor 13a of the modulated wave input means S13 in the first embodiment. Is connected to one end. The connection point between the resistor 13a and the inductor 33 is grounded via the capacitor 34. GaAs
The source of the sFET 31 is connected to the capacitor 23a and the inductor 23b of the modulation wave input means 23 in the modulation circuit 20.
Is connected to the connection point. Other configurations of the modulation circuits 10 and 20 are the same as those in FIG. 1 of the first embodiment.

In the modulator shown in FIG. 6, a modulated wave S2 is input to the gate of the GaAs FET 31 via the input circuit 30. The GaAs FET 31 generates a drive signal S3 corresponding to the modulated wave S2 by the power supply 32 and outputs the drive signal S3 to the source. This drive signal S3 is input to the modulated wave input means 13 and 23 instead of the modulated wave S2. The modulation circuits 10 and 20 in which the drive signal S3 is input to the modulation wave input means 13 and 23 instead of the modulation wave S2 operate in the same manner as in the first embodiment, and the modulated wave Vout is output from the output terminal Out. Is done. As described above, in the second embodiment, the GaAs
An sFET 31 is provided to generate a drive signal S3, and the drive signal S3 is replaced with the modulated wave input means 13, 2 instead of the modulated wave S2.
3, the modulated wave S2 can have a small current value, and a stable MMIC-based modulator can be realized.

Note that the present invention is not limited to the above embodiment, and various modifications are possible. For example, there are the following modifications. (I) Although the FETs 12, 22, and 31 are MES-type FETs, other HMET or MOS-type FETs can be used, and bipolar transistors can also be used. (Ii) Modulated wave input means 13 and 23, carrier wave input means 1
1. The modulated wave output means 25 and the like have a simple configuration using a capacitor, but may have a configuration in which an inductor and a capacitor are combined and connected in a complicated manner or a distributed transmission line.

[0018]

As described above in detail, according to the first aspect, the modulator is composed of the two stages of the first modulation circuit and the second modulation circuit, so that the level of the modulated wave is low. The amplitude of the modulated wave at that time can be made sufficiently small, and the modulation index can be improved. According to the second and third aspects, the carrier wave input means for transmitting the carrier wave without alteration, the first and second modulated wave input means for transmitting the modulated wave without alteration,
And the second transistor, and the modulated wave output means for transmitting the modulated wave to the output terminal without altering the modulator, so that the modulator of the first invention can be realized. The cost can be reduced. According to the fourth and fifth aspects, in the modulator according to the second or third aspect, the third transistor is provided, and the first conduction electrode of the first transistor and the third conduction state of the second transistor are provided. The electrode is supplied with a signal obtained by driving the modulated wave by the power supply by the third transistor via the first and second modulated wave input means. For example, the current of the modulated wave input from the outside is supplied to the electrode. The size can be reduced, and a stable modulator can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of a modulator showing a first embodiment of the present invention.

FIG. 2 is a schematic circuit diagram showing a conventional modulator.

FIG. 3 is a diagram showing simulation data of a modulation characteristic and a modulation index in a conventional modulator that can be easily converted to an MMIC.

FIG. 4 is a characteristic diagram showing a DC characteristic and a load line of the GaAsFET 12 in FIG.

FIG. 5 is a diagram showing a modulation characteristic and a modulation index of FIG. 1;

FIG. 6 is a schematic circuit diagram of a modulator according to a second embodiment of the present invention.

[Explanation of symbols]

 10, 20 Modulation circuit 11 Carrier input means 12, 22, 31 GaAs FET 13, 23 Modulation wave input means 14, 24 Self-bias circuit 25 Modulated wave output means S1 Carrier S2 Modulated wave Vout Modulated wave

Claims (5)

[Claims] A first modulation circuit for modulating a carrier with a modulation wave; and a second modulation for generating a modulated wave by further modulating the carrier modulated by the first modulation circuit with the modulation wave. A modulator comprising: a circuit. 2. The first modulation circuit comprises: a carrier input means for transmitting the carrier input from a first input terminal without altering the carrier; a first conductive electrode, a second conductive electrode, and the carrier. A first control electrode connected to input means for controlling a conduction state between the first and second conduction electrodes, and a first transistor for amplifying the carrier wave and outputting the amplified carrier wave to the first conduction electrode Transmitting the modulated wave input from the second input terminal to the first conductive electrode of the first transistor without alteration, and converting the carrier wave amplified by the first transistor with the modulated wave. The second modulation circuit is connected to a third conduction electrode, a fourth conduction electrode, and a first conduction electrode of the first transistor. The third controlling the conductive state between the third and fourth conductive electrodes And a control electrode,
A second transistor that amplifies the modulated carrier wave and outputs the amplified carrier wave to the third conductive electrode; and a third transistor of the second transistor without modifying the modulated wave input from the second input terminal. The second modulated wave input means for generating the modulated wave by further modulating the carrier wave modulated by the modulated wave by applying the carrier wave modulated by the modulated wave, without modifying the modulated wave 2. A modulated wave output means for transmitting the modulated wave to an output terminal.
A modulator as described. 3. The first and second transistors are GaAs field-effect transistors formed on a common GaAs substrate, wherein the carrier input means, the first modulation wave input means, and the second modulation 3. The modulator according to claim 2, wherein the wave input means and the modulated wave output means are constituted by passive elements formed on the common GaAs substrate. 4. A fifth conductive electrode connected to a power supply, a sixth conductive electrode connected to the first and second modulated wave input means, and a fifth conductive electrode connected to the second input terminal. And a third control electrode for controlling a conductive state between the fifth and sixth conductive electrodes, wherein the modulated wave is supplied from the second input terminal to the third control electrode, and the modulated wave is driven. 4. The modulator according to claim 2, further comprising a third transistor for supplying the converted signal to the first and second modulated wave input means. 5. The modulator according to claim 4, wherein said third transistor comprises a GaAs field effect transistor formed on said common GaAs substrate.