JP2006080698A - Frequency conversion method and frequency converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for simultaneously realizing the generation of a local oscillation signal and frequency conversion by a high-frequency oscillation circuit using an annular resonator, and hence to simplify the structure of a frequency converter and to reduce costs. <P>SOLUTION: A serial-feedback high-frequency oscillation circuit is provided using a semiconductor amplification element, and the input terminal of a high-frequency signal and an intermediate frequency band signal is provided on a microstrip line 12. A point existing at a position of a half wavelength from an input terminal in terms of electric length, is connected to the input transmission line of the semiconductor amplification element, and a stub of prescribed characteristic impedance is provided at a point existing at a position of a 1/4 wavelength from the input terminal in terms of electric length. A carrier component is composed from the output terminal of the semiconductor amplification element with the oscillation frequency of the high-frequency oscillation circuit as the local oscillation signal and a signal frequency-converted with the intermediate frequency band signal as the sideband component is output. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a frequency conversion method and apparatus for use at high frequencies such as millimeter waves or microwaves, and more particularly to a technique for realizing frequency conversion by a simple method by setting a desired high-frequency oscillation frequency.

Conventionally, when converting an intermediate frequency band signal to a radio frequency band signal, the local oscillation signal from the local oscillator is simultaneously input to the frequency converter, and the carrier signal component in the radio frequency band and its sideband component An output signal consisting of The output signal is transmitted through an amplifier.
As is well known, this configuration is complicated because it requires a local oscillator, and there is a problem that it is difficult to realize a stable local oscillator at a high frequency such as a millimeter wave band.

Conventionally, a series feedback oscillator using a transistor is known as a high-frequency oscillation circuit used in a local oscillator or the like. 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 1 discloses the structure of a dielectric resonator.

JP 2003-283247 A

In a high-frequency oscillator using a dielectric resonator, as shown in FIG. 16, 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. 17, 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 1, 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. 16 and 17 are not quantitatively determined, causing manufacturing difficulty and cost increase.

  Further, FIG. 18 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 the 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.
As described above, a local oscillator particularly used for frequency conversion is required to be stable in frequency, so that it is expensive and has a complicated structure.

  The present invention was created in view of the above-described problems of the prior art, and provides a technique for simultaneously generating a local oscillation signal and frequency conversion by a high frequency oscillation circuit using a ring resonator. Thus, the structure of the frequency converter is simplified and the cost is reduced.

In order to solve the above-described problems, the present invention provides the following ring resonator configuration.
That is, the invention described in claim 1 provides a frequency conversion method using a series feedback type high frequency oscillation circuit using a semiconductor amplifying element.
In this method, a microstrip line ring resonator whose line has an electrical length of one wavelength is used, and a high frequency signal and an intermediate frequency band signal are input together from an input terminal on the microstrip line.
A point at a half wavelength position in electrical length from the input terminal is connected to the input transmission line of the semiconductor amplifying element, and a predetermined characteristic impedance is set at a point at a quarter wavelength in electrical length from the input terminal. A stub part is provided.
According to this configuration, a carrier wave component is configured from the output terminal of the semiconductor amplifying element using the oscillation frequency of the high-frequency transmission circuit as a local oscillation signal, and the frequency conversion is performed using the intermediate frequency band signal as its sideband component. .

  According to the second aspect of the present invention, it is possible to provide a frequency conversion method in which the frequency conversion amount can be changed by grounding the stub portion via a variable capacitor and changing the capacitance of the variable capacitor. .

The present invention can also be provided as a frequency converter. That is, a frequency converter including a series feedback type high-frequency oscillation circuit using a semiconductor amplifying element, wherein input terminals for a high-frequency signal and an intermediate frequency band signal are provided on the microstrip line, while the input terminal The point at the half-wavelength in electrical length is connected to the input transmission line of the semiconductor amplifying element.
Further, a stub portion having a predetermined characteristic impedance is provided at a point that is 1/4 wavelength in electrical length from the input terminal, and the oscillation frequency of the high-frequency oscillation circuit is used as a local oscillation signal from the output terminal of the semiconductor amplifying element. And a frequency-converted signal is output using the intermediate frequency band signal as its sideband component.

  The invention according to claim 4 provides a frequency converter in which the stub portion is grounded via a variable capacitor, and the frequency conversion amount can be changed by changing the capacitance of the variable capacitor. You can also.

  The invention according to claim 5 provides a configuration in which the variable capacitor is a varactor diode, and a frequency conversion amount can be changed by adjusting a voltage applied to the varactor diode.

  According to a sixth aspect of the present invention, in the frequency converter, the semiconductor amplifying element is an FET, the ring resonator is connected to a gate circuit, a signal after frequency conversion is output from a source circuit, and a drain circuit Is provided with an open stub.

  According to the present invention, by using the ring resonator according to the present invention, the amount of frequency conversion can be designed analytically and quantitatively, and can contribute to high-accuracy frequency conversion by stable high-frequency oscillation. . In particular, downsizing and stabilization can be achieved with a simple configuration that does not use a local 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, this configuration can change the resonance frequency by a 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 castle, and a transmission line having a length of λ / 2 can be formed between the transmission lines at the passing frequency.
In FIG. 1, when the characteristic impedance of the upper ring portion of the ring resonator (1) is Z ₁ , the characteristic impedance of the lower ring portion is Z ₂ , and the characteristic impedance of the stub portion (5) is 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. 8 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. 9, 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. 10, 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. 11 shows the frequency / phase characteristics of Γ and Γ _L. As can be seen from FIG. 11, the value of the attenuation pole frequency is the frequency at the intersection (Γ = Γ _L ) of Γ and Γ _L in FIG. 11, 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.

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.

The configuration of the ring resonator according to the present invention is as described above. In the present invention, a high frequency oscillation circuit is configured using the ring resonator, and a frequency converter using the high frequency oscillation circuit is provided.
FIG. 2 shows a frequency converter (10) according to the present invention, which uses a ring resonator (11) having a microstrip line length of one wavelength. The intermediate frequency band signal (IF) is input (13) together with the high frequency signal (RF) from the input side end (12) of the ring resonator (11).
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 output signal subjected to frequency conversion is output (20) from the source circuit (19) of the FET (15), and an open stub (22) is provided in the drain circuit (21).

According to the above configuration, high-frequency signal oscillation is realized by a high-frequency oscillation circuit using a ring resonator, and by inputting an intermediate frequency band signal (IF) to the input, the high-frequency signal is converted into a carrier component and an intermediate frequency. The band signal is frequency-converted to obtain an output signal that becomes a sideband component.
That is, according to the above-described high-frequency oscillation circuit, when the capacitance of the variable capacitor is 0, the oscillation frequency characteristic as shown in FIG. 3 can be obtained. A steep oscillation characteristic is shown in the vicinity of 9.3 GHz, and the characteristics of a stable and steep oscillation circuit using the ring resonator of the present invention have been demonstrated.

And the output characteristic when the intermediate frequency band signal of 25 MHz is input at this time is the spectrum shown in FIG. As shown in the figure, sideband components are formed on both sides of the 9.3 GHz carrier component with a separation of 25 MHz.
FIG. 5 shows output characteristics when an intermediate frequency band signal of 100 MHz is input. Here, sideband components are also formed 100 MHz apart.
Thus, in the present invention, unlike the conventional configuration in which a local oscillator is separately provided and converted by the frequency converter, the frequency is converted by inputting a signal different from the oscillation frequency to the ring resonator, as shown in the figure. Spectrum can be obtained.

  As described above, the frequency converter of the present invention has a problem in that it is difficult and unstable to design because the position determination has to rely on experience and intuition in the configuration using the conventional dielectric resonator. The frequency conversion amount can be designed in a formal manner by eliminating each characteristic impedance.

Further, when a variable capacitor is provided like the ring resonator shown in FIG. 1, the oscillation frequency characteristics of the high-frequency oscillation circuit change as shown in FIG. The frequency range was 9.24 GHz to 9.37 GHz as a design value, and high frequency oscillation of 9.26 GHz to 9.35 GHz was obtained as an actual measurement value.
By providing the variable frequency oscillation circuit of the present invention with a variable high-frequency oscillation circuit capable of stably performing high-frequency oscillation in such a sufficient frequency range, the frequency conversion amount can be freely changed.

In the present invention, a ring resonator using a variable capacitor is not necessarily used, and an open stub may be used for the stub portion (5) as shown in FIG.
A ring resonator as shown in FIGS. 13 and 14 can also be used. FIG. 13 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. 14 is a schematic view showing another embodiment of the ring resonator. The difference from the configuration of FIG. 12 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. 15 is a characteristic diagram of the ring filter of FIG. 14 when Z ₁ = 50Ω, Z ₂ = 131.8Ω, and Z ₃ = 70.7Ω (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 frequency converter of this invention. It is a frequency characteristic figure by the high frequency oscillation circuit concerning the present invention. It is a characteristic view which shows the result of the frequency conversion by the frequency converter of this invention. It is a characteristic view which shows the result of the frequency conversion by the frequency converter of this invention. It is a frequency characteristic diagram by the variable high frequency oscillation circuit according to 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 schematic diagram of another embodiment 3 of the ring resonator according to the present invention. It is a frequency characteristic figure by another Example 3 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

DESCRIPTION OF SYMBOLS 10 Frequency converter 11 Ring resonator 12 Input side end 13 Each signal input of RF and IF band 14 Output side end 15 FET
16 Gate circuit 17 Stub section 18 Varactor diode 19 Source circuit 20 Output signal after frequency conversion 21 Drain circuit 22 Open stub

Claims (6)

A frequency conversion method using a series feedback type high frequency oscillation circuit using a semiconductor amplification element,
Using a microstrip line ring resonator whose electrical length is one wavelength,
While inputting the high frequency signal and the intermediate frequency band signal together from the 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, by providing a stub portion with a predetermined characteristic impedance at a point at an electrical length of ¼ wavelength from the input terminal,
A frequency conversion method comprising: forming a carrier wave component from the output terminal of the semiconductor amplifying element using the oscillation frequency of the high-frequency transmission circuit as a local oscillation signal, and frequency-converting the intermediate frequency band signal as its sideband component. The stub portion is grounded via a variable capacitor,
The frequency conversion method according to claim 1, wherein a frequency conversion amount can be changed by changing a capacitance of the variable capacitor. A frequency converter having a series feedback type high frequency oscillation circuit using a semiconductor amplification element,
While providing input terminals for high frequency signals and intermediate frequency band signals 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,
In addition, a stub portion having a predetermined characteristic impedance is provided at a point at an electrical length of ¼ wavelength from the input terminal,
A carrier wave component is configured using the oscillation frequency of the high-frequency transmission circuit as a local oscillation signal from an output terminal of the semiconductor amplifying element, and a frequency-converted signal is output using the intermediate frequency band signal as its sideband component. To frequency converter. The stub portion is grounded via a variable capacitor,
The frequency converter according to claim 3, wherein a frequency conversion amount can be changed by changing a capacitance of the variable capacitor. The variable capacitor is a varactor diode,
The frequency converter according to claim 4, wherein the frequency conversion amount can be changed by adjusting a voltage applied to the varactor diode. In the frequency converter, the semiconductor amplifying element is an FET,
The variable high-frequency oscillator according to claim 3 or 4, wherein the ring resonator is connected to a gate circuit, a signal after frequency conversion is output from a source circuit, and an open stub is provided in a drain circuit.

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