JPH1093348A - Voltage controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the circuit configuration with ease of MMIC and to provide linearity between a DC bias voltage and an oscillation frequency. SOLUTION: The voltage controlled oscillator 11 is provided with a negative resistance circuit 12 consisting of an HEMT 14 and of a feedback circuit applying positive feedback to the HEMT 14 and with a resonance circuit 13 connecting to the negative resistance circuit 12, and the oscillation frequency is variably controlled by varying a DC bias voltage fed to the HEMT 14. In this case, a feedback amount of the feedback circuit is shifted from a point where an absolute resistance of the negative resistor is maximized when viewing the HEMT 14 from an output terminal of the HEMT 14 thereby reducing the negative resistance. Through the constitution above, the DC bias voltage and the oscillation frequency have a linearity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator used when radio waves such as microwaves and millimeter waves are used.

[0002]

2. Description of the Related Art When using radio waves in a frequency band such as a microwave and a millimeter wave, an oscillator for generating a high-frequency signal in the above-mentioned frequency band is required. On the other hand, when frequency modulation (FM) of a high-frequency signal is performed, a voltage-controlled oscillator (VCO) that variably controls the oscillation frequency with an applied voltage is used as an oscillator that can variably control the oscillation frequency. Here, the basic configuration of the oscillator is shown in FIG. FIG. 13 (a)
Is a band-pass type oscillator, and FIG. 13B is a band rejection type oscillator.

As shown in FIGS. 13 (a) and 13 (b),
The oscillator 1 includes a negative resistance circuit 2 having an action of amplifying a signal and a resonance circuit 3 for determining an oscillation frequency. As the negative resistance circuit 2, a feedback circuit in which positive feedback is applied to an active element such as a transistor, or an element having a negative resistance (for example, a Gunn diode) is used. The resonance circuit 3 includes a cavity resonator, a dielectric resonator, a planar resonator, and the like. Further, the band-pass type oscillator 1 (FIG. 13A) is an oscillator that extracts a signal from the resonance circuit 3 side, and is a band rejection type oscillator 1.
(FIG. 13B) is an oscillator that extracts a signal from the negative resistance circuit 2 side.

In the case of the oscillator having the above configuration, in the initial stage of the oscillation, a signal flows between the negative resistance circuit and the resonance circuit, and is strengthened by the negative resistance circuit and the frequency is selected by the resonance circuit. As a result, a state is reached in which steady oscillation occurs at the set frequency. The output power during steady oscillation depends on the amplifying ability of the negative resistance circuit, that is, the strength of the negative resistance.
Generally, the strength of the negative resistance is evaluated by the resistance component of the impedance when the transistor side is viewed from the side closer to the output terminal of the transistor in the feedback circuit of the negative resistance circuit. In the oscillator, the higher the output power is, the more advantageous it is usually. Therefore, the feedback circuit is designed so that the negative resistance is maximized.

In the oscillator having the above configuration, the oscillation frequency can be variably controlled by changing the frequency characteristic of either the negative resistance circuit or the resonance circuit. Here, an example of the voltage controlled oscillator (band rejection type voltage controlled oscillator) is shown in FIG. In the voltage controlled oscillator 1 shown in FIG. 14, a variable capacitance diode (hereinafter referred to as a varactor) 4 is provided in the resonance circuit 3 and the capacitance of the varactor 4 is varied by a voltage applied to the frequency control voltage terminal 5. The resonance frequency of the resonance circuit 2 is varied, so that the oscillation frequency of the voltage controlled oscillator 1 is varied.

Voltage controlled oscillator 1 using varactor 4
In, the frequency range can be set relatively freely by selecting an appropriate varactor 4 according to the frequency range to be controlled. However, when the entire voltage controlled oscillator 1 is configured by one integrated circuit to reduce the circuit size, that is, when the integrated circuit is configured by a monolithic microwave integrated circuit (hereinafter, referred to as MMIC), the varactor 4 and the transistor ( Or a Gunn diode), it is very difficult to convert the entire voltage controlled oscillator 1 into an MMIC.

On the other hand, a configuration in which a voltage controlled oscillator without using a varactor is formed into an MMIC is disclosed in Japanese Patent Laid-Open No. 62-207.
No. 006. FIG. 15 shows this MMIC-based voltage controlled oscillator. The configuration of FIG. 15 is a band-pass type voltage-controlled oscillator 1 in which a transistor, for example, a field-effect transistor (hereinafter referred to as FET) 6 is provided in a resonance circuit 2, and the above-mentioned F
By varying the gate-source capacitance of the FET 6 by the gate bias voltage applied to the ET 6, the resonance frequency of the resonance circuit 3 is varied, and thus the voltage controlled oscillator 1
Is configured to be variable.

In the above configuration, since the transistors (FETs) using the same semiconductor film structure are used for both the negative resistance circuit 2 and the resonance circuit 3, the entire voltage controlled oscillator 1 is mounted on one semiconductor substrate. Can be integrated,
It is easy to convert to MMIC.

[0009]

When a voltage controlled oscillator is used in a frequency modulation circuit, the linearity (proportional relationship) between the control voltage applied to the voltage controlled oscillator and the oscillation frequency is increased.
Is desirably held. On the other hand, when frequency modulation is performed using a voltage controlled oscillator, conventionally, the frequency modulation width (swing width) is about several MHz. As long as this level of frequency modulation is performed, there is no practical problem with the above-described voltage-controlled oscillator having the conventional configuration (an oscillator using the varactor 4 or an MMIC oscillator).

On the other hand, the present inventor has set the center frequency of the oscillation frequency of the voltage controlled oscillator to 30 GHz or 60 GHz.
It was considered to set the frequency to about GHz and to set the swing width to several tens of MHz or more. At the same time, the present inventor has considered making a voltage controlled oscillator that oscillates in the above-mentioned frequency band into an MMIC. In order to fulfill these demands, the present inventor has prototyped a voltage controlled oscillator 11 having an electric circuit configuration shown in FIG. Hereinafter, this voltage controlled oscillator 11
Will be described in detail. (Note that FIG. 1 is an electric circuit diagram showing the first embodiment of the present invention, but since the electric circuit diagram of the prototyped voltage controlled oscillator 11 is the same as FIG. This will be described with reference to Fig. 1. The prototyped voltage controlled oscillator 11 is not publicly known at the time of filing the present invention.) The voltage controlled oscillator 11 has a negative resistance circuit 12 as shown in Fig. 1. And a resonance circuit 13. The negative resistance circuit 12 includes, for example, a high electron mobility transistor (hereinafter, referred to as HEMT) 14 as a transistor,
It comprises a transmission line 15 for applying series feedback to the source of the HEMT 14, a matching circuit 16, and a DC element capacitor 17. In this case, one end of the transmission line 15 is connected to the source of the HEMT 14, and the other end is grounded. The matching circuit 16 includes a transmission line 18 and a stub 19
And a high-frequency grounding capacitor 20 connected in series.

One end of the transmission line 18 (the terminal opposite to the terminal connected to the stub 19) is connected to the drain of the HEMT 14. A connection point between the stub 19 and the high-frequency grounding capacitor 20 is a voltage terminal 21 for supplying a drain bias. The other end of the high-frequency grounding capacitor 20 is grounded. Further, one end of the DC element capacitor 17 is connected to a connection point between the transmission line 18 and the stub 19.
The other end of 7 is an output terminal 22.

On the other hand, the resonance circuit 13 is composed of a planar resonator in which a transmission line 23 and a capacitor 24 are connected in series. One end of the transmission line 23 (the capacitor 24
Are connected to the gate of the HEMT 14. Transmission line 23 and capacitor 2
4 is connected to a voltage terminal 2 for supplying a gate bias.
It is 5. This gate bias is also a control voltage (that is, a DC bias voltage) for controlling the oscillation frequency of the voltage controlled oscillator 11. The other end of the capacitor 24 is grounded.

The circuit elements (ie, the HEMT 14 and the transmission line 1) constituting the voltage-controlled oscillator 11 are
5, 18, 23, stub 19, capacitors 17, 20,
24) is formed, for example, integrally on an InP substrate, whereby the voltage controlled oscillator 11 is manufactured as an MMIC. This fabricated (prototype) voltage controlled oscillator 11
Is an oscillator that oscillates and outputs a high-frequency signal in, for example, a 30 GHz band.
MIC.

The HE formed on the InP substrate is
The MT 14 is a HEMT using an InAlAs / strained InGaAs heterostructure, and has a gate length of 0.5 μm, a unit gate width of 13 μm, and four fingers. When manufacturing the above MMIC,
As the transmission line and the stub, a coplanar line 26 having the configuration shown in FIG. 2 was used. This coplanar line 26 is
A signal line 28 provided on a P substrate 27 and the signal line 2
8 and ground electrodes 29, 29 arranged on both sides. Here, the signal line 28 and the ground electrode 29 were formed of, for example, gold. Then, the width Ws of the signal line 28 is set to 5
The distance Wg between the signal line 28 and the ground electrode 29 was 43 μm. In this case, the wavelength of the high frequency signal of 30 GHz in the coplanar line 26 was calculated to be about 3900 μm.

Further, the present inventor has proposed that the above-mentioned voltage controlled oscillator 1
When fabricating a prototype 1 (MMIC), the feedback circuit was designed such that the strength of the negative resistance of the negative resistance circuit 12 (that is, the strength of the feedback) was maximized. The reason for this design is to maximize the output power of the high-frequency signal oscillated from the voltage controlled oscillator 11 and to stabilize the output.

Here, the strength of the negative resistance is HEMT.
14, the capacitor 20, and the S-parameter of the transmission line 15 were obtained by calculating based on the measurement results.
Specifically, by changing the length Lb of the transmission line 15 shown in FIG. 1 and calculating the impedance Za when the HEMT 14 is viewed from the drain electrode, which is the output terminal of the HEMT 14, the absolute value of the negative resistance component is calculated. (| Re (Za)
|, Where Re (Za) <0) was determined.

As a result of this calculation, it was found that when Lb = 112 μm, the negative resistance was the strongest, that is, the absolute value of the negative resistance was the largest. The value of the negative resistance in this case was Re (Za) =-104Ω. Therefore, the inventor sets the length Lb of the transmission line 15 of the negative resistance circuit 12 to 1121 μm, and sets the length of the transmission line 23 of the resonance circuit 13 and the length of the transmission line 18 and the stub 19 of the matching circuit 16. Each of the lengths is set so that a high frequency signal in a 30 GHz band is oscillated.
(MMIC) prototype was produced.

The inventor measured the voltage (gate bias) -oscillation frequency characteristics of the voltage controlled oscillator 11 manufactured as described above. In this case, the drain bias applied to the voltage terminal 21 was set to 2.5V. Then, the gate bias applied to the voltage terminal 25 is changed from 0.20 V to -0.0.
The oscillation frequency and output power were measured while finely changing the voltage up to 30V. At this time, the gate bias is 0.00
For the voltage range from V to -0.20 V, the measurement is performed by changing the gate bias particularly finely in steps of, for example, 0.01 V. For the remaining voltage range, for example, 0.0
The measurement was performed by changing the gate bias at intervals of 5V.

FIG. 3 is a graph of the above measurement results. In FIG. 3, “diamond (square) points” indicate frequency characteristics, and “circular points” indicate output power characteristics. From FIG. 3 described above, the present inventor has discovered that the above-produced voltage controlled oscillator 11 has a characteristic that the oscillation frequency changes stepwise (stepwise) in response to a change in gate bias. It can be seen that the output power is about 1-2 dBm, and that the output is sufficiently large (that is, the output is maximum).

However, the characteristic that the oscillation frequency changes stepwise indicates that the linearity of the change in the oscillation frequency with respect to the control voltage (gate bias) is not maintained. Therefore, the prototype voltage controlled oscillator 11 cannot be used for a frequency modulation circuit.

Therefore, the present inventor cannot manufacture the voltage-controlled oscillator 11 which is realized as the MMIC by manufacturing as described above so that the DC bias voltage (gate bias) and the oscillation frequency have linearity. I thought. Here, the inventor paid attention to the feedback strength of the feedback circuit in the negative resistance circuit 12 of the voltage controlled oscillator 11. When the feedback strength of the feedback circuit is the maximum, the stability of the oscillation is highest (the Q value is the largest), so that the oscillation frequency is hard to change. In other words, the oscillation frequency is variable. I think it will be difficult to control
The inventor has thought. Further, if this idea is advanced and the stability of the oscillation is reduced so that the oscillation frequency is likely to change, the control voltage (gate bias) and the oscillation frequency may become linear. The inventor has made the hypothesis that there is not.

To confirm the above hypothesis, the present inventor
An experiment was conducted to produce a voltage controlled oscillator 11 (MMIC) in which the feedback strength of the feedback circuit was smaller than the maximum. Then, when the voltage (gate bias) -oscillation frequency characteristic of the manufactured voltage controlled oscillator 11 was measured, it was actually confirmed that the linearity of the change of the oscillation frequency with respect to the gate bias was sufficiently maintained. The specific configuration and measurement results of the voltage controlled oscillator 11 (MMIC) in which the linearity is sufficiently maintained will be described in detail in the section of the embodiment of the invention.

An object of the present invention is to provide a voltage controlled oscillator which has a circuit configuration which can be easily formed into an MMIC and has a configuration in which a DC bias voltage and an oscillation frequency have linearity.

[0024]

According to the first aspect of the present invention, the amount of feedback of the feedback circuit is shifted from the point at which the absolute value of the negative resistance when the transistor side is viewed from the output terminal of the transistor becomes maximum. The negative resistance is configured to be small. As a result, it was possible to sufficiently maintain the linearity of the change in the oscillation frequency with respect to the DC bias voltage. The voltage-controlled oscillator according to the first aspect has an MMI
It is also a circuit configuration that can be easily converted to C.

According to the second or third aspect of the present invention, the direct current bias voltage and the oscillation frequency are set by setting the feedback strength of the feedback circuit to be smaller than the maximum and setting the oscillation output to be smaller than the maximum. Are configured to have linearity, the same operation and effect as the first aspect of the invention can be obtained. Further, even if the feedback circuit is configured such that the DC bias voltage and the oscillation frequency have linearity as in the invention of the fourth aspect, the same operation and effect as the invention of the first aspect can be obtained.

Further, in the invention according to claim 5, the feedback circuit is constituted by a series feedback system in which a transmission line is provided between the transistor and the ground electrode, and the length of the transmission line is reduced.
The length shortened by the length corresponding to several% of the wavelength in the transmission line from the length under the condition where the absolute value of the negative resistance when the transistor side is viewed from the output terminal of the transistor is maximized, Alternatively, the length is set to be shorter than the shortened length. In this case, since the feedback circuit is a series feedback system, the strength of the feedback can be easily adjusted only by adjusting the length of the transmission line, so that the design workability when manufacturing the MMIC is improved. Can be.

Further, according to the invention of claim 6, the transistor is constituted by a field effect transistor, the transmission line of the feedback circuit is provided between the source electrode and the ground electrode of the field effect transistor, and the DC bias voltage is adjusted. Since the configuration is such that the gate bias is used, the voltage-controlled oscillator having the above-described excellent effects can be easily realized with a simple configuration.

Further, according to the invention of claim 7, there is provided an amplifier circuit for amplifying the oscillation output, the amplifier circuit comprising one or a plurality of transistors and a matching circuit for matching these transistors. Therefore, even if the output power of the oscillation output output from the voltage controlled oscillator is reduced, the oscillation output can be amplified to a required level. Also, since the transistor used in this amplifier circuit can be the same type of transistor used in the negative resistance circuit of the voltage controlled oscillator,
The amplifier circuit and the voltage controlled oscillator can be configured as one MMIC chip.

On the other hand, also in the inventions of claims 8 to 10, since the DC bias voltage and the oscillation frequency can be configured to have linearity, it is possible to obtain substantially the same operation and effect as in the invention of claim 1. it can.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. The first
The circuit configuration of the voltage controlled oscillator according to the embodiment is basically the same as the circuit configuration of the voltage controlled oscillator 11 prototyped by the inventor described in the section of “Problems to be Solved by the Invention”.
The difference is that the strength of the negative resistance of the negative resistance circuit 12 (that is,
(The absolute value of the negative resistance component) is made smaller than the maximum. Hereinafter, the voltage controlled oscillator 11 according to the first embodiment will be described in detail with reference to FIG.

First, the circuit configuration of the voltage controlled oscillator 11 will be briefly described. That is, the voltage controlled oscillator 11 includes a negative resistance circuit 12 and a resonance circuit 13, and the negative resistance circuit 12 includes the HEMT 14, the transmission line 15, and the matching circuit 1
6 and a DC element capacitor 17.
The matching circuit 16 includes a transmission line 18, a stub 19, and a high-frequency grounding capacitor 20. A connection point between the stub 19 and the high-frequency grounding capacitor 20 is a voltage terminal 21 for supplying a drain bias. One end of a DC element capacitor 17 is connected to a connection point between the transmission line 18 and the stub 19, and the other end of the DC element capacitor 17 is an output terminal 22.

The resonance circuit 13 is composed of a planar resonator having a transmission line 23 and a capacitor 24. One end of the transmission line 23 is a HEMT of the negative resistance circuit 12.
14 gates. A connection point between the transmission line 23 and the capacitor 24 is a voltage terminal 25 for supplying a gate bias. This gate bias is a control voltage for controlling the oscillation frequency of the voltage controlled oscillator 11, that is,
It is also a DC bias voltage.

Now, in the circuit configuration of the voltage controlled oscillator 11 described above, the strength of the negative resistance of the negative resistance circuit 12 is made smaller than the maximum. Specifically, the length Lb of the transmission line 15 was set to 1048 μm. This length Lb = 104
8 μm is the transmission line length L of the prototyped voltage controlled oscillator.
The length is about 70 μm shorter than b = 1121 μm (the condition of the maximum negative resistance). This shortened length (about 7
0 μm) is a length corresponding to about 2% of the wavelength in the transmission line 15. The wavelength in the transmission line 15 can be obtained by calculation. In the case of the present embodiment, since the transmission line 15 is constituted by the coplanar line 26 shown in FIG. 2, the width dimension Ws of the signal line 28 of the coplanar line 26 and
It was calculated from the distance Wg between the signal line 28 and the ground electrode 29 and the dielectric constant of the InP substrate 27 by a known calculation method. According to this calculation, the wavelength in the transmission line 15 is about 3900 μm.
m.

Then, as described above, the negative resistance circuit 12
When the length Lb of the transmission line 15 was set to 1048 μm, the value of the negative resistance was Re (Za) = − 96Ω. As a result, it can be seen that the strength of the negative resistance of the negative resistance circuit 12 is smaller than the maximum (Re (Za) = − 104Ω). In other words, it can be seen that the feedback strength of the feedback circuit of the negative resistance circuit 12 is set smaller than the maximum.

When the length Lb of the transmission line 15 of the negative resistance circuit 12 is changed, the conditions of the resonance circuit 13 and the matching circuit 16 also change. The lengths of the transmission line 18 and the stub 19 are adjusted so that a high-frequency signal in a 30 GHz band is oscillated. Further, the voltage controlled oscillator 11 having such a configuration
(HEMT 14, transmission lines 15, 18, 23, stub 1
9, capacitors 17, 20, and 24) are integrally formed on an InP substrate, and thus constitute an MMIC. FIG. 5 shows an actual circuit pattern of the MMIC. The components indicated by the reference numerals and the lead lines in FIG. 5 are the same as the configurations indicated by the reference numerals and the lead lines in FIG. In FIG. 5, a hatched area indicates a capacitor.

The control voltage (gate bias) -oscillation frequency characteristic of the voltage controlled oscillator 11 configured as described above was measured. In this case, the drain bias applied to the voltage terminal 21 was set to 2.5V. Then, the gate bias applied to the voltage terminal 25 is changed from 0.20 V to -0.0.
The oscillation frequency and output power were measured while finely changing the voltage up to 30V. Specifically, the gate bias is set to 0.0
The measurement was carried out while changing minutely at 1 V intervals.

FIG. 4 is a graph of the above measurement results. In FIG. 4, “diamond (square) points” indicate frequency characteristics, and “circular points” indicate output power characteristics. As can be seen from FIG. 4, the voltage controlled oscillator 11 of the first embodiment is
In (2), it was clearly confirmed that the oscillation frequency changes linearly with the change of the gate bias, that is, that the gate bias (DC bias voltage) and the oscillation frequency have extremely good linearity. In the first embodiment, the negative resistance of the negative resistance circuit 12 is reduced.
Accordingly, it can be seen that the output power is in the range of about −7 dB to −5 dB, that is, the output power is reduced.

In the above embodiment, the negative resistance circuit 12
Is set to 1048 μm by shortening the length Lb of the transmission line 15 by a length corresponding to about 2% of the wavelength in the transmission line 15, but the present invention is not limited to this. The length Lb of the 12 transmission lines 15 is
It may be set shorter than 8 μm. Specifically, the inventor manufactured a voltage controlled oscillator (MMIC) 11 in which the length Lb of the transmission line 15 was shortened by a length corresponding to about 6% of the wavelength in the transmission line 15 and set to 891 μm. did.
And, in this manufactured voltage controlled oscillator 11,
It was confirmed by measurement that the gate bias (DC bias voltage) and the oscillation frequency had extremely good linearity.

Table 1 below summarizes the experimental results of the voltage controlled oscillators of the above two products and the prototype.

[0040]

[Table 1]

As is clear from this table, the transmission line 15
If the length Lb of the feedback circuit is reduced to reduce the feedback amount of the feedback circuit, that is, if the absolute value of the negative resistance of the feedback circuit is reduced, the linearity between the gate bias (DC bias voltage) and the oscillation frequency is improved. It can be seen that it has. According to the above table, when the length Lb of the transmission line 15 is reduced, the linearity is not lost, but the output power (oscillation output) is gradually reduced.

According to the above table, the maximum value of the length Lb of the transmission line 15 in the case of linearity is the length (Lb = Lb = Lb) of the transmission line 15 under the condition that the strength of the negative resistance is the maximum. 112
1 μm), which is shorter by a length corresponding to about 2% of the wavelength in the transmission line 15. In this case, the output power is the largest, so that the oscillator is most easily used. However, the present inventor has set the length Lb of the transmission line 15 to be approximately one wavelength less than that of the condition in which the strength of the negative resistance is the maximum.
% Or about 1.5%, the voltage-controlled oscillator 11 was shortened by a length equivalent to about 1.5% or the like. However, such a voltage-controlled oscillator 11 having the transmission line 15 of each length was manufactured. It is preferable to confirm whether each has linearity. In other words, since there is no theoretical support at present, the linearity of the voltage-controlled oscillator 11 under various conditions can be determined only by actually manufacturing the voltage-controlled oscillator 11 and confirming whether or not the manufactured device has linearity. There is no way to determine the boundary conditions between those with and without.

In this case, if it is found that the oscillator has linearity, the larger the output power is, the more preferable the oscillator is.
Among the ICs, it is preferable to use the one having the longest length Lb of the transmission line 15, that is, the one having the largest feedback strength of the feedback circuit.

In the above embodiment, the voltage controlled oscillator 1
Although the center value of the oscillation frequency of 1 was set to 30 GHz, the invention is not limited to this.
GHz or more (for example, 60 GHz),
The frequency may be set to 30 GHz or less.

Further, in the above embodiment, the InP substrate is used, but a GaAs substrate may be used instead. Further, in the above embodiment, the transmission line is constituted by a coplanar line, but may be constituted by a microstrip line. Furthermore, in the above embodiment, the transistor of the negative resistance circuit 12 is constituted by the HEMT 14, but
However, the present invention is not limited to this, and may be constituted by another FET (field effect transistor), or may be constituted by a bipolar transistor (for example, a hetero bipolar transistor).

On the other hand, in the above embodiment, the negative resistance circuit 12
The length of the transmission line 15 is shortened so that the strength of the feedback of the feedback circuit is shifted from the maximum to be reduced. However, the present invention is not limited to this.
The length of 5 is the case where the strength of the negative resistance is the maximum, and the length of the other transmission lines and stubs and the capacitance of the capacitors are adjusted to reduce the oscillation output, thereby improving the linearity. You may comprise so that it may have. Further, in the above embodiment, the resonance circuit 13 is configured by a planar resonator, but may be configured by a dielectric resonator, a diode resonator, a cavity resonator, or the like instead.

FIGS. 6 to 8 show a second embodiment of the present invention. Differences from the first embodiment will be described. The same parts as those in the first embodiment are denoted by the same reference numerals. In the second embodiment, an amplifier circuit 30 for amplifying the oscillation output of the voltage controlled oscillator 11 of the first embodiment is provided, and the amplifier circuit 30 and the voltage controlled oscillator 11 are connected to each other by one.
And one MMIC.

As shown in FIG. 6, the amplifying circuit 30
It comprises an input matching circuit 31, a HEMT 32, an output matching circuit 33, and a capacitor. The input matching circuit 31 includes a transmission line 35, a stub 36, and a capacitor 3.
7 are connected in series. In this case, the connection point between the transmission line 35 and the stub 36 is connected to the output terminal of the voltage controlled oscillator 11 (the other end of the DC blocking capacitor 17). In addition, one end of the transmission line 35 (the terminal opposite to the terminal connected to the stub 36) is connected to the gate of the HEMT 32. One end of the capacitor 37 (terminal opposite to the terminal connected to the stub 36) is grounded. Furthermore,
The connection point between the stub 36 and the capacitor 37 is
A voltage terminal 38 for supplying a gate bias of 32 is used.

The output matching circuit 33 is connected to the transmission line 3
9, a stub 40 and a capacitor 41 are connected in series. In this case, the connection point between the transmission line 39 and the stub 40 is connected to one end of the capacitor 34. In addition, one end of the transmission line 39 (terminal opposite to the terminal connected to the stub 40) is connected to the drain of the HEMT 32. One end of the capacitor 41 (terminal opposite to the terminal connected to the stub 40) is grounded. Further, a connection point between the stub 40 and the capacitor 41 is a voltage terminal 42 for supplying a drain bias of the HEMT 32.

The source of the HEMT 32 is grounded. This HEMT 32 is a HEMT of the negative resistance circuit 12.
It has the same semiconductor film structure as T14. The HEMT 32 has a gate length of 0.5 μm, a unit gate width of 25 μm, and two fingers. The other end of the capacitor 34 (the transmission line 39)
(Terminal on the opposite side to the terminal connected to the connection point of the stub 40)
Are the output terminals 43 of the amplifier circuit 30. The output terminal 43 takes out the amplified oscillation output.

Further, the input matching circuit 31 and the output matching circuit 33 are configured so that the gain in the 30 GHz band is maximized, and so-called gain matching is achieved. Also,
The transmission lines 35 and 39 and the stubs 36 and 4 of the amplifier circuit 30
Numeral 0 is constituted by a coplanar line 26 in the same manner as the transmission line and the stub of the voltage controlled oscillator 11 (the negative resistance circuit 12 and the resonator 13).

The amplifying circuit 30 and the voltage controlled oscillator 11 having such a configuration are integrally formed on an InP substrate, thereby forming one MMIC.
FIG. 7 shows an actual circuit pattern of this MMIC. The components indicated by the reference numerals and the lead lines in FIG. 7 are the same as the configurations indicated by the reference numerals and the lead lines in FIG. In FIG. 7, a hatched area indicates a capacitor.

The MMIC constructed as described above
A control voltage (gate bias) -oscillation frequency characteristic of the (voltage controlled oscillator 11 and the amplifier circuit 30) was measured. In this case, the drain bias of the HEMT 14 of the voltage controlled oscillator 11 (the voltage applied to the voltage terminal 21) was set to 2.5V. Further, the gate bias of the HEMT 32 (voltage applied to the voltage terminal 38) of the amplifier circuit 30 was set to 0V. Further, the drain bias (voltage applied to the voltage terminal 42) of the HEMT 32 was set to 2.5V. Then, the gate bias (DC bias voltage) applied to the voltage terminal 25 is finely changed from 0.00 V to about −0.40 V, specifically, while changing the voltage at a step of 0.01 V,
The oscillation frequency and output power were measured.

FIG. 8 is a graph of the above measurement results. In FIG. 8, “diamond (square) points” indicate frequency characteristics, and “circular points” indicate output power characteristics. As shown in FIG. 8, also in the second embodiment, the oscillation frequency changes linearly with the change in the gate bias, that is, the gate bias (DC bias voltage) and the oscillation frequency have extremely good linearity. Was clearly confirmed. Further, in the second embodiment, it can be seen that the output power was in the range of about 1 dB to 2 dB, that is, high output power was obtained.

In the second embodiment, the voltage-controlled oscillator 11 and the amplifier circuit 30 are configured as one MMIC. However, the present invention is not limited to this. For example, a mixer, a frequency multiplier, a power amplifier, or the like may be used. Circuit is voltage controlled oscillator 1
1 (or a combination of the voltage controlled oscillator 11 and the amplifier circuit 30) to form one MMIC.

FIG. 9 shows a third embodiment of the present invention, and the points different from the first embodiment will be described. The same parts as those in the first embodiment are denoted by the same reference numerals. In the third embodiment, the transmission line 15 of the first embodiment is not provided, that is, the source of the HEMT 14 is configured to be directly grounded, and between the gate and the drain of the HEMT 14, Transmission line 44 and capacitor 45
Were connected in series. Thus, the negative resistance circuit 12 is configured to apply feedback in a parallel feedback system.

In the case of the above configuration, by changing the length of the transmission line 44 and changing the capacitance of the capacitor 45, the feedback strength of the feedback circuit can be adjusted so as to be weaker than the maximum. That is, by adjusting the length of the transmission line 44 and the capacitance of the capacitor 45, it is possible to configure so that the gate bias (DC bias voltage) and the oscillation frequency have linearity. It should be noted that, compared to the configuration in which feedback is performed by the parallel feedback system as in the third embodiment, the configuration in which feedback is performed in the series feedback system as in the first or second embodiment is more effective. The adjustment of the strength is easy, and the design is easy.

FIG. 10 shows a fourth embodiment of the present invention, and different points from the first embodiment will be described. still,
The same parts as those in the first embodiment are denoted by the same reference numerals.
In the fourth embodiment, the HEMT 4
6 is provided, and the oscillation frequency is varied by changing the gate capacitance by a bias voltage applied to the gate of the HEMT 46.

Specifically, the drain and the source of the HEMT 46 are grounded, and the gate of the HEMT 46 is connected to the transmission line 47.
And the capacitor 48 are grounded through a series circuit.
The connection point between the transmission line 47 and the capacitor 48 is a voltage terminal 49 for applying a gate bias (control voltage or DC bias voltage). The gate of the HEMT 46 is connected to a connection point between the transmission line 23 and the capacitor 24 via a capacitor 50.

The bias supply circuit 51 is connected to the gate of the HEMT 14 of the negative resistance circuit 12. This bias supply circuit 51 is configured by connecting a transmission line 52 and a capacitor 53 in series. One end of the transmission line 52 (the terminal opposite to the terminal connected to the capacitor 53) is connected to the gate of the HEMT 14 and the transmission line 23 of the resonance circuit 13. One end of the capacitor 53 (terminal opposite to the terminal connected to the transmission line 52) is grounded. A connection point between the transmission line 52 and the capacitor 53 is a voltage terminal 54 for supplying a bias.

The configuration of the fourth embodiment other than that described above is the same as the configuration of the first embodiment. Therefore, in the fourth embodiment, substantially the same operation and effect as in the first embodiment can be obtained.

In the resonance circuit 13 of the fourth embodiment, a variable capacitance diode (varactor) 55 having the configuration shown in FIG. 11 may be used instead of the HEMT 46. Also in the case of the fifth embodiment, the oscillation frequency can be varied by changing the capacitance of the varactor 55 by the control voltage, and the same operation and effect as in the fourth embodiment can be obtained.

FIG. 12 shows a sixth embodiment of the present invention, and the differences from the fourth embodiment will be described. still,
The same parts as those in the fourth embodiment are denoted by the same reference numerals.
In the sixth embodiment, the negative resistance circuit 1 of the fourth embodiment is used.
Second, the negative resistance circuit of the third embodiment, that is, the parallel feedback negative resistance circuit is used. Otherwise, the configuration of the sixth embodiment is the same as the configuration of the fourth embodiment. Therefore, also in the sixth embodiment, the same operation and effect as in the fourth embodiment can be obtained.

In the resonance circuit 13 of the sixth embodiment, a variable capacitance diode (varactor) 55 having the configuration shown in FIG. 11 may be used instead of the HEMT 46. Also in the case of this configuration, the oscillation frequency can be varied by changing the capacitance of the varactor 55 by the control voltage, and the same operation and effect as in the sixth embodiment can be obtained.

In each of the third to seventh embodiments, the amplifier circuit for amplifying the oscillation output, for example, the amplifier circuit 30 of the second embodiment may be integrally provided as one MMIC. good. In each of the third to seventh embodiments, circuits such as a mixer, a frequency multiplier, and a power amplifier are combined with the voltage-controlled oscillator 11 (or a combination of the voltage-controlled oscillator 11 and the amplifier circuit 30). 1
It may be configured as one MMIC.

[Brief description of the drawings]

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

FIG. 2 is a partial perspective view of a coplanar line.

FIG. 3 is a characteristic diagram of a prototype.

FIG. 4 is a characteristic diagram of the first embodiment.

FIG. 5 is an enlarged view showing a circuit pattern of the MMIC;

FIG. 6 is a view corresponding to FIG. 1, showing a second embodiment of the present invention;

FIG. 7 is a diagram corresponding to FIG. 5;

FIG. 8 is a diagram corresponding to FIG. 4;

FIG. 9 is a view corresponding to FIG. 1, showing a third embodiment of the present invention.

FIG. 10 is a view corresponding to FIG. 1, showing a fourth embodiment of the present invention;

FIG. 11 is a partial electric circuit diagram showing a fifth embodiment of the present invention.

FIG. 12 is a view corresponding to FIG. 1, showing a sixth embodiment of the present invention;

FIG. 13 is a block diagram of an oscillator showing a conventional configuration.

FIG. 14 is a diagram corresponding to FIG. 1 showing a different conventional configuration.

FIG. 15 is a diagram corresponding to FIG. 1 showing a further different conventional configuration.

[Explanation of symbols]

11 is a voltage controlled oscillator, 12 is a negative resistance circuit, 13 is a resonance circuit, 14 is a high electron mobility transistor (HEM).
T), 15 is a transmission line, 16 is a matching circuit, 21 is a voltage terminal, 22 is an output terminal, 23 is a transmission line, 24 is a capacitor, 25 is a voltage terminal, 26 is a voltage terminal, 26 is a coplanar line, 30 is an amplifier circuit, and 32 is a high Electron mobility transistor (HEM
T) and 44 are transmission lines, 45 is a capacitor, 46 is a high electron mobility transistor (HEMT), and 55 is a variable capacitance diode.

Claims (10)

[Claims] A resonant circuit comprising a transistor, a feedback circuit for applying a positive feedback to the transistor, and a resonance circuit, wherein the oscillation frequency is variably controlled by varying a DC bias voltage applied to the transistor. In the configured voltage controlled oscillator, the amount of feedback of the feedback circuit is shifted from a point where the absolute value of the negative resistance when the transistor side is viewed from the output terminal of the transistor becomes maximum, thereby reducing the negative resistance. A voltage controlled oscillator characterized by having such a configuration. 2. A semiconductor device comprising: a transistor; a negative resistance circuit including a feedback circuit for applying a positive feedback to the transistor; and a resonance circuit, wherein the oscillation frequency is variably controlled by varying a DC bias voltage applied to the transistor. In the configured voltage controlled oscillator, a voltage is characterized in that the DC bias voltage and the oscillation frequency are configured to have linearity by setting a feedback strength of the feedback circuit to be smaller than a maximum. Controlled oscillator. And a resonance circuit comprising a transistor, a feedback circuit for applying a positive feedback to the transistor, and a resonance circuit, wherein the oscillation frequency is variably controlled by varying a DC bias voltage applied to the transistor. In the voltage controlled oscillator having the above configuration, the DC bias voltage and the oscillation frequency have linearity by setting an oscillation output smaller than a maximum. 4. A semiconductor device comprising: a transistor; a negative resistance circuit including a feedback circuit for applying a positive feedback to the transistor; and a resonance circuit, wherein the oscillation frequency is variably controlled by varying a DC bias voltage applied to the transistor. In the voltage controlled oscillator configured, the feedback circuit is configured such that the DC bias voltage and the oscillation frequency have linearity. 5. The feedback circuit according to claim 1, wherein the feedback circuit is configured in a series feedback system in which a transmission line is provided between the transistor and a ground electrode, and the length of the transmission line is determined by looking at a transistor side from an output terminal of the transistor. A few% of the wavelength in the transmission line, compared to the length under the condition that the absolute value of the negative resistance is maximized.
2. The voltage-controlled oscillator according to claim 1, wherein the length is set to be shorter than the length corresponding to the length, or not more than the shortened length. 6. The transistor comprises a field effect transistor, a transmission line of the feedback circuit is provided between a source electrode and a ground electrode of the field effect transistor, and the DC bias voltage is a gate bias. The voltage controlled oscillator according to claim 5, wherein 7. An amplifier circuit for amplifying the oscillation output, wherein the amplifier circuit includes one or more transistors,
7. The voltage controlled oscillator according to claim 1, wherein said voltage controlled oscillator comprises a matching circuit for matching with said transistors. 8. A negative resistance circuit comprising a transistor and a feedback circuit for applying a positive feedback to the transistor; and a resonance circuit having a capacitor whose capacity can be variably controlled by a voltage. In the voltage controlled oscillator configured to variably control the oscillation frequency by changing, the feedback amount of the feedback circuit is such that the absolute value of the negative resistance when the transistor side is viewed from the output terminal of the transistor is maximized. A voltage-controlled oscillator configured to reduce the negative resistance by shifting the negative resistance. 9. A negative resistance circuit comprising a transistor and a feedback circuit for applying a positive feedback to the transistor; and a resonance circuit having a capacitor whose capacity can be variably controlled by a voltage. In the voltage controlled oscillator configured to variably control the oscillation frequency by changing, the direct current bias voltage and the oscillation frequency are linearized by setting the feedback strength of the feedback circuit to be smaller than the maximum. A voltage-controlled oscillator characterized by having: 10. The feedback circuit is configured by a parallel feedback system in which a transmission line and a capacitor are provided between an input terminal and an output terminal of the transistor, and the length of the transmission line and the capacitance of the capacitor are: By shifting from the condition that the absolute value of the negative resistance when the transistor side is viewed from the output terminal of the transistor is maximized,
9. The voltage controlled oscillator according to claim 1, wherein the negative resistance is reduced.