JP2006080697A - Ring oscillator and variable high frequency oscillator employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for stably varying a resonance frequency of a ring oscillator in a small scale and to provide a small-sized variable high frequency oscillator whose oscillated frequency range is wide and stable. <P>SOLUTION: The variable high frequency oscillator 10 of a series feedback type employing the variable ring resonator is disclosed. The high frequency oscillator 10 employing the microstrip line ring resonator 11 whose electric length of the line of which is one wavelength is configured such that an input side terminal 12 for a high frequency signal is provided onto the line, a point 14 located apart from the input side terminal 12 by a half wavelength in terms of the electric length is connected to an input transmission line of a FET, and further a stub part 17 with a prescribed characteristic impedance is provided to a point apart from the input side terminal 12 by 1/4 wavelength in terms of the electric length. The stub part is connected to ground via a variable capacitor. The resonance frequency of the ring resonator and the oscillated frequency of the high frequency oscillator are changed by varying the capacitance of the variable capacitor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ring resonator for use at a high frequency such as millimeter wave or microwave, and a variable high frequency oscillator using the ring resonator, and particularly relates to a technique capable of freely obtaining a desired resonance frequency or oscillation frequency. is there.

A ring resonator disclosed in Patent Document 1 is a conventionally known ring resonator.
According to this technique, in the stripline ring resonator, four terminals are provided which are connected to each point obtained by dividing the line length into four at equal intervals through a coupling circuit. A resonant capacitor is connected between the first point on the line and a second point located at a distance of 1/2 of the line length, and the first point is separated from the line length by 1/4. A resonant capacitor is connected between the third point at the position and the fourth point at a position separated from the third point by a line length of ½.

Thereby, orthogonal resonance modes in which the resonance frequency can be arbitrarily set can be used, and the frequency adjustment can be easily realized by the capacitance value of the resonance capacitor.
However, in this method, it is necessary to connect a resonance capacitor, and it is necessary to reduce the size and stabilize the resonance frequency by making it possible to set the resonance frequency more easily.

Patent No. 3309454

Conventionally, a series feedback oscillator using a transistor is known as a high-frequency oscillation circuit. Examples of the resonator used in the oscillator include a dielectric resonator and a YIG resonator, and the former is widely used.
For example, Patent Document 2 discloses the structure of a dielectric resonator.

JP 2003-283247 A

In a high-frequency oscillator using a dielectric resonator, as shown in FIG. 12, the dielectric resonator (42) is arranged at a certain distance from an appropriate position of the input transmission line (41) of the FET (40). The desired oscillation frequency is determined while adjusting.
In the adjustment, as shown in FIG. 13, the dielectric resonator (42) is placed at a position higher than the high-frequency circuit board (43), and the distance between the oscillator jig (44) and the dielectric resonator (42) is set to be conductive. Adjust the oscillation frequency by adjusting with screws.

  As disclosed in Patent Document 2, since the resonance frequency fluctuates depending on the temperature and pressure, such adjustment must rely on experience and intuition. The positions indicated by X, Y, h, and d in FIGS. 12 and 13 are not quantitatively determined, which causes manufacturing difficulty and cost increase.

  Furthermore, FIG. 14 shows a voltage-controlled oscillator using a dielectric resonator (50), a λ / 4 microstrip transmission line (51), and a varactor diode (52) as a technique for enabling the oscillation frequency of a high-frequency oscillator. The structure of is shown. In this technique, a transmission line (51) and a varactor diode (52) are attached to the dielectric resonator (50) and the semiconductor amplifying element (53) on the opposite side of the input transmission line (54). The oscillation frequency is configured to be variable by adjusting the voltage applied to the varactor diode (52).

  However, even in this configuration, the oscillation frequency must be adjusted by adjusting the position of the dielectric resonator (50) as described above, and in order to realize a certain oscillation frequency range, it is necessary to rely on experience and intuition. There is no problem. Further, the oscillation frequency range could not be made sufficiently wide.

  The present invention has been created in view of the above-described problems of the prior art, and is a technique for changing the resonance frequency of a ring resonator in a small and stable manner, and has a wide oscillation frequency range, a small and stable structure. It is an object of the present invention to provide a variable high frequency oscillator.

In order to solve the above-described problems, the present invention provides the following ring resonator configuration.
That is, the invention according to claim 1 is a microstrip line ring resonator in which the electrical length of the line is one wavelength, and an input terminal for a high-frequency signal is provided on the microstrip line, and from the input terminal A point at a half wavelength position in electrical length is connected to the input transmission line of the semiconductor amplifying element, and a stub portion having a predetermined characteristic impedance is provided at a point at a quarter wavelength in electrical length from the input terminal. The stub portion is grounded via a variable capacitor.
Thus, the resonance frequency can be changed by changing the capacitance of the variable capacitor.

  According to a second aspect of the present invention, there is provided a ring resonator in which the variable capacitor is a varactor diode and the resonance frequency can be changed by adjusting a voltage applied to the varactor diode. .

The present invention can also provide a variable high frequency oscillator. That is, the invention according to claim 3 uses a microstrip line ring resonator in which the oscillation frequency is variable and the electrical length of the line is one wavelength in a series feedback type high frequency oscillator using a semiconductor amplifying element. A high-frequency signal input terminal is provided on the microstrip line, and a point at an electrical length and a half-wavelength from the input terminal is connected to the input transmission line of the semiconductor amplifying element, and further from the input terminal A stub portion having a predetermined characteristic impedance is provided at a long and 1/4 wavelength position, and the stub portion is grounded via a variable capacitor.
Thus, the oscillation frequency can be changed by changing the capacitance of the variable capacitor.

  According to the invention of claim 4, the variable capacitor is a varactor diode, and the oscillation frequency can be changed by adjusting the voltage applied to the varactor diode. The variable high frequency oscillator configured as described above can be provided as a voltage controlled oscillator.

  According to the fifth aspect of the present invention, in the variable high-frequency oscillator, the semiconductor amplifying element is an FET, the ring resonator is connected to the gate circuit, an oscillation signal is output from the source circuit, and the drain circuit is supplied. Can provide a variable high frequency oscillator with an open stub.

  According to the configuration of the first or second aspect of the present invention, the resonance frequency can be quantitatively set by setting each characteristic impedance of the ring resonator, and in particular, the size can be reduced by a simple configuration for changing the capacitance of the variable capacitor. In addition, a stable resonator can be provided. In particular, in the configuration of claim 2, the resonance frequency can be freely changed by voltage control.

  According to the third or fifth aspect of the present invention, the above-described ring resonator is applied to a high-frequency oscillator, thereby contributing to the realization of a small and stable variable high-frequency oscillator.

Hereinafter, embodiments of the present invention will be described based on examples shown in the drawings. The embodiment is not limited to the following.
First, the structure of a ring resonator having a variable resonance frequency according to the present invention will be described. As a first embodiment of the ring resonator, a ring resonator (1) realized by a microstrip line as shown in FIG. 1 can be mentioned.

  In the ring resonator (1), the ring is a microstrip line having an electrical length of one wavelength (λ) at a passing frequency, and on the line, an input side end (2) and an output side end (3) of the resonator. Are provided at positions separated by λ / 2 in electrical length. Further, a stub portion (5) having an electrical length of λ / 4 is connected to a position (4) that is separated from the input side end (2) by an electrical length of λ / 4 on the ring circumference. In the following description, in the description of the line length, all are described as meaning the electrical length.

  In the present invention, one end of a varactor diode (9) is connected to the stub portion (5) as a variable capacitor whose capacity can be changed by an applied voltage, and the other end is grounded. As will be described later with this configuration, the resonance frequency can be changed by voltage, but a known device other than the varactor diode (9) can be used as the variable capacitor.

According to this configuration, the one-sided circuit at the bisection point can be cut off at the passband, and a transmission line having a length of λ / 2 can be formed between the transmission lines at the passing frequency.
In Figure 1, Z ₁ the characteristic impedance of the upper ring portion of the ring resonator (1), characteristic impedance Z ₂ of the lower ring portion, the characteristic impedance of the open stub (5) When Z _3, the attenuation pole frequency f is obtained by the following equation (1).

(Equation 1) tan ² θ _p = 2 (1 + Z ₁ / Z ₂ ) × Z ₃ / Z ₂
f = θ _p ° / 90 ° x f ₀ (GHz) (f ₀ is the center frequency)

For example, the ring resonator (1) is formed on a high-frequency circuit board having a relative dielectric constant of 3.5, a substrate thickness of 1.67 mm, a conductor thickness of 35 μm, and a dielectric loss of 0.025. The effective radius of the ring is 15 mm and the length of the open stub is about 20 mm. Each characteristic impedance at this time was measured for frequency characteristics when Z ₁ = 50Ω, Z ₂ = 131.8Ω, and Z ₃ = 24.6Ω.

The high frequency characteristics of the ring resonator at this time are as shown in FIG. In the figure, the upper side shows the pass characteristic and the lower side shows the group delay characteristic. The passage loss in the 2 GHz band is about 0.28 dB, and the attenuation pole frequencies are about 800 MHz and about 3200 MHz, which are found to be in good agreement with the theoretical values (792 MHz, 3208 MHz) obtained by the above equation 2. Further, the specific bandwidth exceeds 100%, and the group delay characteristic is about 1 ns (constant) at 2 GHz ± 0.4 GHz, which is almost the value of the transmission line.
As described above, the ring resonator has a steep attenuation characteristic, and is also characterized by a flat group delay characteristic and a flat and low loss frequency characteristic of the passband, which is superior to a conventional dielectric resonator. Has characteristics.

Next, the analysis of the attenuation pole frequency related to each characteristic impedance of the ring resonator will be described. FIG. 5 is a diagram for explaining the S matrix in the ring resonator (1). When the ports # 1 to # 3 are defined as shown in the figure, the S matrix at this time is expressed by the following equation (2).

Then, as shown in FIG. 6, when the resonance circuit is treated as a two-port device between the input side end and the output side end, and the reflection coefficient of the stub portion is Γ, the S matrix at this time is expressed by Equation 3. The

The resonance condition S _21R = 0 is Γ = Γ _L , and the output side matching Γ _L is expressed by Equation 4.

Here, each characteristic impedance was Z ₁ = 62.3Ω, Z ₂ = 90Ω, Z ₃ = 50Ω, and the passing characteristics when the center frequency was 6.5 GHz were measured. The result is shown in FIG.
In FIG. 7, the reflection characteristic S ₁₁ and the transmission characteristic S ₂₁ are shown, and the attenuation pole frequencies are 3.9 GHz and 9.1 GHz.

FIG. 8 shows the frequency / phase characteristics of Γ and Γ _L. As can be seen from FIG. 8, the value of the attenuation pole frequency is the frequency at the intersection (Γ = Γ _L ) of Γ and Γ _L in FIG. 8, and is determined by Γ.
Utilizing such characteristics, in the present invention, a varactor diode (9) is disposed in the stub portion (5) to change the characteristic of Γ.

That is, when the capacitance C of the variable capacitor is 0 pF, the characteristics of the graph (30) are shown as described above, and the attenuation pole frequencies are 3.9 GHz and 9.1 GHz, but by changing the capacitance C, The graph moves and the intersection of Γ and Γ _L changes.
For example, when C = 0.2 pF, the frequency changes to 3.3 GHz and 8.3 GHz, and when C = 0.5 pF, the frequency changes to 2.9 GHz and 7.6 GHz.
Thus, according to the present invention, the attenuation pole frequency is changed by changing the voltage applied to the varactor diode (9).

Next, the Q value of this ring resonator will be considered.
In general, since the dielectric resonator has a high Q value, the output waveform from an oscillator stabilized by the dielectric resonator is characterized by high signal purity. Therefore, the phase noise characteristic which is one of the indicators of signal purity is excellent. For this reason, the dielectric resonator stabilization voltage control oscillator may be used for an apparatus for generating a reference signal.

The Q value of the ring resonator according to the present invention can be expressed by Equation 5. As shown in Equation 5, the Q value is determined by each characteristic impedance, and simulations and demonstration experiments based on this formula show that the Q value of the ring resonator is sufficiently high.

With the above configuration, the characteristics of the ring resonator change, and if this is used as a band filter, it is possible to provide a filter whose stop band or pass band changes by voltage control, for example.
In addition, the ring resonator according to the present invention can be applied to any device. Hereinafter, the case of using as a variable high frequency oscillator will be described.

  That is, FIG. 2 shows a variable high-frequency oscillator (10) according to the present invention, which uses a ring resonator (11) having a microstrip line length of one wavelength. The input side end (12) of the ring resonator (11) is terminated with 50Ω (13), and the output side end (14) is connected to the gate circuit (16) of the FET (15) as a semiconductor amplifying element.

As shown in FIG. 1, the ring resonator is provided with a stub (17) having an electrical length of ¼ wavelength. As described above, the resonance frequency can be changed by the varactor diode (18). An applied voltage is input to the varactor diode (18) by a DC power source (not shown).
An oscillation signal is output (20) from the source circuit (19) of the FET (15), and an open stub (22) is provided in the drain circuit (21).

As described above, the high-frequency oscillator of the present invention solves the problem that the design using a conventional dielectric resonator has to rely on experience and intuition to determine the position, which is difficult and unstable in design. In addition, it has become possible to formally design by defining each characteristic impedance.
FIG. 3 is a measurement result showing the oscillation frequency characteristics of the high-frequency oscillator (10) shown in FIG. 2. The design value is a frequency range of 9.24 GHz to 9.37 GHz, and the actual measurement value is 9.26 GHz to 9.35 GHz. High frequency oscillation was obtained.
The present invention can provide a variable high-frequency oscillator capable of stable high-frequency oscillation in such a sufficient frequency range. In addition, the structure is simply provided with a varactor diode, which contributes to miniaturization and cost reduction.

In addition to the ring resonator used above, a ring resonator as shown in FIGS. 9 and 10 can also be used. FIG. 9 shows a ring resonator using a rectangular ring instead of the circular ring shown in FIG.
The present invention may be configured in any manner as long as the electrical length and impedance are the same regardless of the shape of such a ring.
Note that the microstrip lines 6 and 7 connected to the input terminal and the output terminal are provided to suppress signal reflection, and the characteristic impedance Z ₀ is attenuated as can be seen from Equation 1. It does not affect the pole frequency.

FIG. 10 is a schematic view showing another embodiment of the ring resonator. The difference from the configuration of FIG. 1 is that the length of the stub portion (5) connected to the position (4) away from the input side end (2) by λ / 4 is λ / 2, and the tip is grounded. It is that.
The ring resonator with an open stub in FIG. 1 can widen the frequency interval between the attenuation poles, but attenuation does not occur when the frequency is zero, whereas the ring resonator with a shorted stub has a frequency interval between the attenuation poles. Although not as wide as in the case of an open stap, when the frequency is zero (and a frequency twice the center of the vortex center), there is a feature that the signal is not passed.

FIG. 11 is a characteristic diagram when Z ₁ = 50Ω, Z ₂ = 131.8Ω, and Z ₃ = 70.7Ω in the ring filter of FIG. 10 (the upper side is a pass characteristic and the lower side is a reflection characteristic). When the passing center frequency is 2 GHz, the reduced tail frequencies are about 1.4 GHz and 2.6 GHz, and the interval is narrower than in the case of the open stub (800 MHz and 3.2 GHz), but when the frequency is zero and 4 GHz (passing center) It can be seen that the frequency is also attenuated at the frequency (frequency multiplied by the frequency).

It is a schematic diagram of one Example of the ring resonator which concerns on this invention. It is a block diagram of the variable high frequency oscillator of this invention. It is a frequency characteristic figure by the variable high frequency oscillator of the present invention. It is a high frequency characteristic figure of a ring resonator. It is a figure for demonstrating S matrix of a ring resonator. It is a figure for demonstrating S matrix of a ring resonator. It is a figure which shows the passage characteristic of a ring resonator. It is a figure which shows the frequency and phase characteristic of (GAMMA) and (GAMMA) _L. It is a schematic diagram of another embodiment 1 of the ring resonator according to the present invention. It is a schematic diagram of another embodiment 2 of the ring resonator according to the present invention. It is a frequency characteristic figure by another Example 2 of the ring resonator which concerns on this invention. It is a figure explaining the structure of the conventional dielectric resonator. It is a figure explaining the structure of the conventional dielectric resonator. It is a figure explaining the structure of the conventional dielectric resonator which can control voltage.

Explanation of symbols

10 High Frequency Oscillator 11 Ring Resonator 12 Input Side End 13 50Ω Termination 14 Output Side End 15 FET
16 Gate circuit 17 Stub section 18 Varactor diode 19 Source circuit 20 Oscillation output 21 Drain circuit 22 Open stub

Claims (5)

A microstrip line ring resonator in which the electrical length of the line is one wavelength,
While providing a high frequency signal input terminal on the microstrip line,
A point located at a half wavelength position in electrical length from the input terminal is connected to the input transmission line of the semiconductor amplifying element,
Furthermore, a stub portion having a predetermined characteristic impedance is provided at a point at a quarter wavelength in electrical length from the input terminal, and the stub portion is grounded via a variable capacitor,
A ring resonator, wherein the resonance frequency can be changed by changing the capacitance of the variable capacitor. The variable capacitor is a varactor diode,
The ring resonator according to claim 1, wherein the resonance frequency can be changed by adjusting a voltage applied to the varactor diode. In the series feedback type high-frequency oscillator using a semiconductor amplifying element, the oscillation frequency is variable,
Using a microstrip line ring resonator whose electrical length is one wavelength,
While providing a high frequency signal input terminal on the microstrip line,
A point located at a half wavelength position in electrical length from the input terminal is connected to the input transmission line of the semiconductor amplifying element,
Furthermore, a stub portion having a predetermined characteristic impedance is provided at a point at a quarter wavelength in electrical length from the input terminal, and the stub portion is grounded via a variable capacitor,
A variable high-frequency oscillator characterized in that the oscillation frequency can be changed by changing the capacitance of the variable capacitor. The variable capacitor is a varactor diode,
The variable high-frequency oscillator according to claim 3, wherein the oscillation frequency can be changed by adjusting a voltage applied to the varactor diode. In the variable high-frequency oscillator, the semiconductor amplifying element is an FET,
The variable high-frequency oscillator according to claim 3, wherein the ring resonator is connected to a gate circuit, an oscillation signal is output from a source circuit, and an open stub is provided in a drain circuit.

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