JPH1056327A - Microwave band voltage-controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to suppress the forward current of the gate electrode of a field-effect transistor small and easily set the optimum position of a dielectric resonator. SOLUTION: This voltage-controlled oscillator is equipped with the dielectric resonator 20 and a field-effect transistor(FE) 10, and one microstrip line 21 is electromagnetically coupled with the dielectric resonator 20; and a varactor diode 24 is connected to this microstrip line 21 and this varactor diode 24 is supplied with a varactor bias voltage from a supply terminal 27. To this varactor diode 24, the gate terminal 10A of the FET 10 is connected through a DC blocking capacitor 28, and a choke coil 29 and a current limiter resistor 30 are connected between the gate terminal 10A and ground. This resistor 30 suppresses the forward current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave voltage controlled oscillator, and more particularly to a voltage controlled oscillator used as a highly stable and high purity signal source in a microwave band communication device or radar device.

[0002]

2. Description of the Related Art Conventionally, a microwave band voltage controlled oscillator using a dielectric resonator is well known. As this kind of voltage controlled oscillator, the dielectric resonator is electromagnetically coupled by a microstrip line. There is a configuration in which a varactor diode (variable capacitance diode) is connected to this microstrip line, and an example is shown in FIG.

In FIG. 4, microstrip lines 2A and 2B are formed so as to be electromagnetically coupled to a dielectric resonator 1, and a varactor diode 3 is connected between the microstrip lines 2A and 2B. The connection point between the anode side of the varactor diode 3 and the microstrip line 2A is grounded via the choke coil 4, and the connection point between the cathode side of the varactor diode 3 and the other microstrip line 2B is connected to the choke coil 5A.
Is connected to the varactor bias voltage supply terminal 6 via

A microstrip line 7 is electromagnetically coupled to the dielectric resonator 1. One end of the microstrip line 7 is connected to a terminating resistor 8, and the other end is a field effect transistor (hereinafter referred to as FET). ) 10 is connected to the gate end 10A. This FET 10 is composed of GaAs
s MES (Gallium Arsenide Metal Semiconductor) FE
The capacitor 12 is connected between the source (S) of the FET 10 and the ground, and a bias resistor 14 is connected via a choke coil 13. On the other hand, a DC voltage supply terminal 16 is connected to the drain (D) side of the FET 10 via the choke coil 15, and an oscillation output terminal 18 is connected via a DC (DC) cut capacitor 17.

According to the configuration of the voltage controlled oscillator described above, the capacitance value of the capacitor 12 is selected by selecting the capacitance value of the capacitor 12 under the operating conditions of the FET 10 determined by the DC voltage applied from the DC voltage supply terminal 16 and the bias resistor 14. 1
The reflection coefficient of the FET 10 from 0A is 1 at the target frequency.
Can be exceeded. When the reflection coefficient exceeds 1, it means that the real component of the impedance becomes negative.

On the other hand, the impedance when the dielectric resonator 1 is viewed from the gate end 10A of the FET 10 has a positive real number component because it is a passive circuit. And FE
Real component of impedance on T10 side and dielectric resonator 1
When the sum of the real components of the impedance on the side is negative and the sum of the respective imaginary components becomes 0, the circuit starts to oscillate at the frequency at that time.

The oscillation frequency can be changed by the voltage supplied from the varactor bias supply terminal 6. That is, when the voltage from the varactor bias supply terminal 6 is changed, the capacitance value of the varactor diode 3 changes.
Electromagnetically transmitted to the dielectric resonator 10 via A and 2B, and as a result, the resonance frequency of the dielectric resonator 10 changes. Therefore, the impedance when the dielectric resonator 1 side is viewed from the gate terminal 10A of the FET 10 also changes, and the oscillation frequency output from the oscillation output terminal 18 changes.

[0008]

Since the conventional microwave band voltage controlled oscillator performs a large-amplitude operation after the start of oscillation, the gate-source voltage VGS of the FET 10 extends to a positive region. This is called a positive transfer to the gate electrode. When the voltage VGS becomes positive,
For example, there is a problem that a forward current flows from the gate electrode into the FET 10 and this current shortens the life of the FET 10.

In addition, if the forward current is large, the change over time in the oscillation characteristics becomes remarkable. Therefore, reducing this forward current is an important issue in oscillator design.
For this reason, conventionally, a countermeasure to suppress the above positive transfer by increasing the gate bias is taken, but in this case, there is a disadvantage that the oscillation output becomes low.

In the above-mentioned microwave band voltage controlled oscillator, two microstrip lines (2A, 2B, 7) are provided as shown in FIG. Therefore, there is a problem that it is difficult to determine the optimum position where the dielectric resonator 1 is arranged.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to reduce the forward current at the gate electrode of a field effect transistor and to optimize the position of a dielectric resonator. Is to provide a microwave band voltage controlled oscillator that can easily set the voltage.

[0012]

According to a first aspect of the present invention, there is provided a microwave controlled voltage oscillator comprising a dielectric resonator and a field effect transistor. A microstrip line is electromagnetically coupled to a varactor, a varactor diode is connected to the microstrip line, and a varactor bias voltage is supplied to the varactor diode. The gate of the field-effect transistor is connected via a gate, and a choke coil and a current limiting resistor are connected between the gate of the field-effect transistor and the ground. The invention according to a second aspect is characterized in that a capacitor and a choke coil are connected between the microstrip line and the varactor diode for DC cut.

According to the above configuration, the gate current, that is, the forward current, can be suppressed low by the current limiting resistor connected to the gate of the field effect transistor via the choke coil. Also, by connecting the varactor diode connected to the microstrip line to the field effect transistor via the DC cut capacitor,
The number of microstrip lines that are electromagnetically coupled to the dielectric resonator can be reduced to one.

[0014]

FIG. 1 shows the configuration of a microwave band voltage controlled oscillator according to a first embodiment of the present invention. As shown in FIG. 1, one microstrip line 21 is formed so as to be electromagnetically coupled to the dielectric resonator 20, and this microstrip line 21 is formed.
Is connected to a terminal resistor 22. A varactor diode 24 (anode side) is connected to the other end of the microstrip line 21 via a DC cut capacitor 23. , A choke coil 25 are arranged.

A varactor bias voltage supply terminal 27 is connected to the cathode side of the varactor diode 24 via a choke coil 26. Therefore, this voltage supply terminal 27
Determines the capacitance value of the varactor diode 24. If this voltage is changed, the capacitance value also changes.

A gate end 10A of a field effect transistor (hereinafter referred to as an FET) 10 is connected to the cathode side of the varactor diode 24 via a DC cut capacitor 28.
It is composed of As MESFET and the like.

In order to satisfy the oscillation condition by each of the above components, the impedance of the dielectric resonator 20 including the capacitance value of the varactor diode 24 and the FET
In the sum of the impedances on the 10 side, the position of the dielectric resonator 20 is selected so that the real component is 0 or negative and the imaginary component is 0 for the target frequency.
In this case, since the dielectric resonator 20 may be positioned with respect to one microstrip line 21, the determination of the optimum position is easier than in the conventional case.

A current limiting resistor 30 is connected between the gate of the FET 10 and the ground via a choke coil 29.
Are connected, and the inductance value is selected so that the choke coil 29 is open in the microwave band. on the other hand,
The current limiting resistor 30 is set to a larger value than the terminating resistor 22 connected to one end of the microstrip line 21, whereby the gate forward current during oscillation can be suppressed.

Further, a capacitor 12 is connected between the source (S) of the FET 10 and the ground, and a bias resistor 14 is connected via a choke coil 13. On the other hand, a DC voltage supply terminal 16 is connected to the drain (D) side of the FET 10 via a choke coil 15, and an oscillation output terminal 18 is connected via a DC cut capacitor 17. Here, under the operating conditions of the FET 10 determined by the DC voltage applied from the DC voltage supply terminal 16 and the bias resistor 14, the real component of the impedance when the FET 10 is viewed from the gate terminal 10A of the FET 10 is a target frequency region. Will select a negative capacitance value.

The voltage-controlled oscillator of the first example has the above configuration. In this oscillator, the sum of the real component is negative and the sum of the imaginary component is 0 in the impedance of the FET 10 and the impedance of the dielectric resonator 1. The frequency at which
Start oscillation. When the voltage supplied from the varactor bias supply terminal 6 is changed, the capacitance value of the varactor diode 24 changes, and the dielectric resonator 10
Will change.

In such an oscillating operation, a positive transfer occurs due to a large amplitude operation after the start of the oscillating operation.
Although a large forward current tends to flow in the ten gate electrodes, in the oscillator of this example, since the current limiting resistor 30 is arranged via the choke coil 29, it is possible to suppress the forward current to a small value. it can.

FIG. 2 shows the configuration of a second example of the embodiment. This second example is another example of manufacturing a voltage controlled oscillator having a different oscillation frequency. As shown in FIG. 2, this second example is a DC cut capacitor (23) of FIG.
And a choke coil (25), and a terminating resistor 32 is arranged at one end of the microstrip line 21 electromagnetically coupled to the dielectric resonator 20. Then, the other varactor diode 24, FET 10, D
The configuration of the C-cut capacitor 28, the choke coil 29, the current limiting resistor 30, and the like are the same as in the first example.

That is, in FIG. 1, in the case of the first example, DC
With the cut capacitor 23 and the choke coil 25,
There is an advantage that the direct current can be cut before the microstrip line 21. Further, in the first example, even when, for example, an open stub (open end pattern) is provided instead of the terminating resistor 22 of the microstrip line 21, the varactor diode 2 in the oscillator is provided.
4 and the like can be satisfactorily secured. However, it is also possible to select a method of grounding via the terminating resistor 32 without using the DC cut capacitor 23 and the like as in the second example.

FIG. 4 shows that the gate width of the FET 10 is 4
A graph is shown in which the oscillation frequencies obtained in the first example circuit and the second example circuit are calculated assuming 00 μm. As shown in the figure, in the case of the first example, the frequency changes in the range of 11.16 to 11.1 GHz with the change of the capacitance of about 0.7 to 3 pF, and in the case of the second example, the same capacitance is used. With change, 1
The frequency changes in the range of 0.95 to 10.9 GHz.

[0025]

As described above, according to the present invention,
Since a choke coil and a current limiting resistor are connected between the gate of the field effect transistor and the ground, the forward current at the gate electrode is suppressed to a small value, the aging characteristics of the oscillation characteristics are small, and a reliable long life is achieved. A voltage controlled oscillator can be obtained. In addition, since one microstrip line is electromagnetically coupled to the dielectric resonator, it is easy to determine the optimum positions of these members, and there is an advantage that the development time is shortened.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram showing a configuration of a microwave band voltage controlled oscillator according to a first example of an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram illustrating a configuration of a microwave band voltage controlled oscillator according to a second example of the embodiment.

FIG. 3 is a graph showing oscillation frequencies obtained in a first example and a second example.

FIG. 4 is an equivalent circuit diagram showing a configuration of a conventional microwave band voltage controlled oscillator.

[Explanation of symbols]

1, 20: Dielectric resonator, 2A, 2B, 7, 21: Microstrip line, 3, 24: Varactor diode, 8, 22, 32: Terminating resistor, 10: FET, 10A: Gate end, 12, 23, 28: DC cut capacitor, 13, 15, 25, 26, 29: choke coil, 30: current limiting resistor.

Claims (2)

[Claims] 1. A microwave band voltage controlled oscillator comprising a dielectric resonator and a field effect transistor, wherein one microstrip line is electromagnetically coupled to the dielectric resonator, and a varactor is connected to the microstrip line. A diode is connected, and a varactor bias voltage is supplied to the varactor diode. The gate of the field effect transistor is connected to the varactor diode via a DC cut capacitor, and the gate of the field effect transistor is grounded. Between
A microwave band voltage controlled oscillator characterized by connecting a choke coil and a current limiting resistor. 2. A microwave band voltage controlled oscillator according to claim 1, wherein a capacitor and a choke coil are connected between said microstrip line and said varactor diode for DC cutoff.