JP2010288133A - Method for designing high frequency circuit, and high frequency circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To raise stability of a high frequency circuit with a small number of components. <P>SOLUTION: In the high frequency circuit having an electronic circuit, a stab connected in parallel with the electronic circuit, and a resistor connected in parallel with the electronic circuit, the resistor is replaced with an equivalent circuit which is a distributed constant circuit, an impedance value of the stab and a resistance value of the equivalent circuit are set so that impedance matching of the high frequency circuit may be obtained at a first frequency to be used in the high frequency circuit and that the high frequency circuit may be stabilized at a second frequency at which the high frequency circuit should be stabilized. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for designing a high-frequency circuit.

  In a high-frequency circuit provided with a high-frequency amplifier circuit, a distributed constant line (stub) or the like is connected in parallel to the transmission line, as in the circuit described in Patent Document 1, in order to stabilize the operation at a desired frequency. Perform matching.

JP 11-261301 A

  However, in high-frequency circuits, even if impedance matching is performed at a desired frequency, it may become unstable at other frequencies.

  Since impedance matching is performed even at the unstable frequency, the number of components increases when components having a desired lumped constant are added. Furthermore, when the frequency at which stability is to be maintained is high, there is a problem in that desired characteristics cannot be obtained because those components appear as distributed constants at a high frequency.

  An object of the present invention is to provide a technique for improving the stability of a high-frequency circuit with a small number of components.

  In order to achieve the above object, a high frequency circuit design method according to the present invention includes an electronic circuit, a stub connected in parallel to the electronic circuit, and a resistor connected in parallel to the electronic circuit. The resistor is replaced with an equivalent circuit which is a distributed constant circuit, and impedance matching of the high-frequency circuit is performed at a first frequency used in the high-frequency circuit, and the high-frequency circuit is stabilized at a second frequency. In this design method, the impedance value of the stub and the resistance value of the equivalent circuit are set so that the high-frequency circuit is stabilized.

  The high-frequency circuit of the present invention includes an electronic circuit, a stub in which an impedance value is set so that impedance matching of the high-frequency circuit can be performed at a first frequency used in the high-frequency circuit, and the stub connected in parallel to the electronic circuit; A resistance value is set so that the high-frequency circuit is stabilized at a second frequency at which the high-frequency circuit is to be stabilized, and a resistor connected in parallel to the electronic circuit.

  According to the present invention, since the resistor inserted in parallel with the electronic circuit is replaced with the distributed constant circuit, impedance matching can be appropriately performed in the high-frequency circuit, so that the stability of the high-frequency circuit can be improved. Further, since it is not necessary to insert components such as coils and capacitors, the number of components can be reduced.

It is an example of the circuit diagram of the high frequency circuit of this embodiment. It is the figure which represented S parameter of the high frequency circuit by 4 terminal matrix. It is an example of the equivalent circuit of the chip resistor of this embodiment. In the high frequency circuit of this embodiment, it is a circuit diagram of a circuit without distributed constant lines, open stubs, and chip resistors. It is a graph which shows the calculation result of the S parameter in the circuit of FIG. It is a figure which shows the Smith chart which plotted the impedance obtained from the circuit of FIG. In the high-frequency circuit of this embodiment, it is a circuit diagram of a circuit without a chip resistor. It is a graph which shows the calculation result of S parameter in the circuit of FIG. 8 is a Smith chart in which impedances obtained from the circuit of FIG. 7 are plotted. FIG. 8 is a Smith chart displaying points on the stability circle obtained from the circuit of FIG. 7. It is a graph which shows the calculation result of S parameter at the time of grasping chip resistance as a lumped constant circuit. 5 is a Smith chart in which S parameters are plotted when a chip resistance is regarded as a lumped constant circuit. It is a Smith chart which displayed the stability circle at the time of considering chip resistance as a lumped constant circuit. It is a flowchart which shows the design method of the high frequency circuit of this embodiment. It is a graph which shows the calculation result of S parameter at the time of grasping chip resistance as a distributed constant circuit. 5 is a Smith chart in which S parameters are plotted when a chip resistance is regarded as a distributed constant circuit. It is a Smith chart which displayed the stability circle at the time of considering chip resistance as a distributed constant circuit.

  Embodiments for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 is an example of a circuit diagram of the high-frequency circuit 1 of the present embodiment. Referring to FIG. 1, the high frequency circuit 1 includes an input terminal 11, a distributed constant line 12, a high frequency amplifier circuit 13, an output matching circuit 14, an output terminal 15, an open stub 16, and a chip resistor 17.

  The distributed constant line 12 is connected to the input terminal 11 of the high frequency circuit 1 and the output terminal of the high frequency amplifier circuit 13. The distributed constant line 12 is a line that is treated as a distributed constant circuit in impedance matching.

  The high-frequency amplifier circuit 13 is a circuit that amplifies a high-frequency signal from the distributed constant line 12, and is a target for impedance matching. The output matching circuit 14 is connected to the output terminal of the high frequency amplifier circuit 13 and the output terminal 15 of the high frequency circuit 1. The output matching circuit 14 is a circuit for adjusting the impedance on the output side of the high-frequency amplifier circuit 13 at a predetermined frequency in the high-frequency circuit 1.

  The open stub 16 is a distributed constant line connected in parallel with the high-frequency amplifier circuit 13. In the present embodiment, the width of the open stub 16 is a fixed value and the length is variable. The designer can adjust the impedance of the open stub 16 by changing the length. The chip resistor 17 is, for example, an SMT (Surface Mount Technology) component inserted between the open stub 16 and the distributed constant line 12.

  A stability circle used for impedance matching will be described. FIG. 2 is a diagram showing the characteristics of the high-frequency amplifier circuit 13 in a 4-terminal matrix called an S parameter. The relationship between the input wave and the reflected wave is expressed by the following equation (1) using this four-terminal matrix.

... (1)
In the above equation (1), S ₁₁ , S ₁₂ , S ₂₁ , and S ₂₂ are S parameters of the high-frequency amplifier circuit 13, a ₁ is an input wave input from the input terminal to the circuit, and b ₁ Is a reflected wave corresponding to a ₁ . a ₂ is an input wave input to the circuit from the output terminal side, and b ₂ is a reflected wave corresponding to a ₂ .

In particular, S ₁₁ is the ratio of the reflected wave b ₁ to the incident wave a ₁ on the input side when the output side is terminated with 50Ω, and is called the input side reflection coefficient. S ₁₂ is the ratio of the reflected wave b ₂ to the incident wave a ₂ on the output side when the input side is terminated with 50Ω, and is called the output side reflection coefficient.

Here, as shown in FIG. 2, the reflection coefficient Γout (S ₁₂ ) on the output side when a load (passive element) having a reflection coefficient Γs is attached to the input terminal is expressed by the following equation (2). In the present embodiment, the distributed constant line 12, the open stub 16, and the chip resistor 17 correspond to a load of Γs.

_{Γout = b 2 / a 2 =} S 22 + {(S 12 * S 21 * Γs / (1-S 11 * Γs)} ··· (2)
At this time, it can be said that the high-frequency circuit 1 is stable if the absolute value of the output reflection coefficient Γout in the above equation (2) is smaller than 1, regardless of where the impedance of Γs is in the Smith chart.

  However, oscillation does not necessarily occur when the absolute value of Γout is 1 or more, and oscillation does not occur when the load impedance is larger than the absolute value of the negative resistance. However, if the absolute value of Γout is 1 or more and the load impedance is less than the absolute value of the negative resistance, oscillation occurs. Thus, the locus of the impedance of Γs at which Γout becomes 1 is important for determining stability.

  Therefore, the stability circle is a diagram illustrating the impedance region of Γs satisfying the following expression (3).

| Γs | ≧ 1 (3)
If the impedance region of Γs satisfying the above equation (3) does not exist in the Smith chart with radius 1, the load impedance value is larger than the absolute value of the negative resistance, and the circuit is stable. . On the contrary, if this impedance region exists in the Smith chart with radius 1, the value of the load impedance is smaller than the absolute value of the negative resistance, and the high-frequency circuit 1 can oscillate. Thus, stability can be visually discriminated by using the stability circle.

  Next, an impedance matching method will be described. In general, impedance matching is performed by the distributed constant line 12 and the open stub 16 so that the frequency of the input signal input from the input terminal 11 is stabilized at a desired frequency. However, as a result of this impedance matching, the added load becomes an unstable load for a certain frequency other than the desired frequency, and the stability as the high-frequency circuit 1 may be impaired.

  Therefore, the chip resistor 17 is inserted at the base of the open stub 16. The insertion of the chip resistor 17 improves the stability of the high-frequency circuit 1 even at an unstable frequency.

  However, when the chip resistor 17 is inserted, the stability of the high-frequency circuit 1 is improved at a certain frequency, but the impedance may be shifted at a desired frequency.

  For this reason, in the impedance matching, the chip resistor 17 is calculated by replacing the equivalent circuit shown in FIG. Referring to the figure, the equivalent circuit includes a capacitor component and an inductance component in addition to a resistance component. Details of the design method when the chip resistor 17 is replaced with an equivalent circuit will be described later with reference to FIG.

  Next, the effect of inserting the chip resistor 17 will be described with reference to FIGS. 5, FIG. 6, and FIGS. 8 to 13 are diagrams showing the results of simulating S parameters and Smith charts using Advanced Design System (registered trademark) manufactured by Agilent Technologies. In the simulation, the width of the open stub 16 was 0.2 mm, and the desired frequency in impedance matching was 10 GHz. It is desirable that the circuit does not oscillate even in a frequency band somewhat higher than 10 GHz. The frequency at which this stability should be maintained was 16 GHz. Further, a FET (Field Effect Transistor) is used as the high frequency amplifier circuit 13.

  Under the above conditions, the impedance value of the open stub 16 and the resistance value of the resistor 17 are made variable, and by appropriately changing these values according to the simulation result, it is possible to appropriately perform impedance matching.

  First, as shown in FIG. 4, in the high frequency circuit 1 of FIG. 1, the distributed constant line 12, the open stub 16 and the chip resistor 17 are not provided, and the input / output terminal of the high frequency amplifier circuit 13 is an ideal 50Ω line. Consider the case of being connected.

FIG. 5 is a graph showing S parameters S ₁₁ and S ₂₁ of the high frequency amplifier circuit 13 calculated for each frequency in the circuit of FIG. In the figure, the solid line is the calculation result of S ₂₁ , and the broken line is the calculation result of S ₁₁ . The vertical axis of the graph is the value of the S parameter, and the unit is decibels. The horizontal axis represents the frequency of signals input to and output from the circuit of FIG. The measurement point “m1” is the value of S _{21 in} the 10 GHz band which is a desired frequency.

FIG. 6 is a Smith chart in which the reflection coefficients obtained from the circuit of FIG. 4 are plotted. In the figure, the solid concentric circles are constant resistance circles. The dotted concentric circles are constant conductance circles. A thick solid line is obtained by plotting and connecting the reflection coefficient S ₁₁ for each frequency obtained from the circuit of FIG. The distance between each point on the thick solid line and the center (○) of the Smith chart is S ₁₁ , and the angle formed by the line connecting each point and the center on the thick solid line with the X axis is the phase. The measurement point “m2” is a point where the value of S _{11 in} the 10 GHz band that is a desired frequency is plotted.

  Referring to FIG. 6, “m2” is not near the center of the Smith chart, and impedance matching is not achieved at a desired frequency. In this case, since the maximum power is not supplied to the high-frequency amplifier circuit 13, the high-frequency circuit 1 has lost the gain.

  5 and 6, impedance matching is not achieved in the circuit in which the open stub 16 and the chip resistor 17 are not provided. For this reason, as shown in FIG. 7, a circuit in which a distributed constant line 12 and an open stub 16 are further added will be considered.

FIG. 8 is a graph showing S parameters S ₁₁ and S ₂₁ calculated for each frequency in the circuit of FIG. In the figure, the measurement point “m1” is a point where the value of S _{11 in} the 10 GHz band is plotted. Referring to the figure, the gain of “m1” is sufficiently high, but in the 16 GHz band, the reflection coefficient (S ₂₁ ) on the output side is considerably lowered, and the impedance phase is almost short.

FIG. 9 is a Smith chart in which S ₁₁ of the entire high-frequency circuit 1 obtained from the circuit of FIG. 7 is plotted. In the figure, the measurement point “m2” is a point where the value of S _{11 in} the 10 GHz band which is a desired frequency is plotted. Referring to the figure, the measurement point of “m2” is located near the center of the Smith chart, and impedance matching is taken at a desired frequency.

FIG. 10 is a Smith chart displaying points on the stability circle that satisfy the above-mentioned expression (3) in the circuit of FIG. In the figure, the measurement point “m3” is one of the measurement points on the outer periphery of the stability circle, and is a point where the value of S ₁₁ at a frequency of 16 GHz is plotted. Referring to the figure, this “m3” has a distance of about 1 from the center (◯) of the Smith chart and is on a circle with a radius of 1. For this reason, depending on a slight phase variation or the like, the measurement point of S ₁₁ may enter an unstable (oscillation) region, that is, a Smith chart with a radius of 1.

  In summary, from FIG. 8 to FIG. 10, the distributed constant line 12 and the open stub 16 added for the purpose of impedance matching at 10 GHz are loads that cause instability of the high-frequency circuit 1 at 16 GHz. .

  Next, in order to alleviate the instability at 16 GHz, consider the circuit shown in FIG. 1, that is, the circuit shown in FIG.

FIG. 11 is a graph showing S parameters S ₁₁ and S ₂₁ of the entire high-frequency circuit 1 calculated for each frequency in the circuit of FIG. Referring to FIG. 11, the addition of the chip resistor 17 increases the reflection coefficient (S ₂₁ ) on the output side in the 16 GHz band compared with the graph shown in FIG.

FIG. 12 is a Smith chart in which S ₁₁ of the entire high-frequency circuit 1 is plotted. In the figure, the measurement point “m2” is a point where the value of S ₁₁ at a frequency of 10 GHz, which is a desired frequency, is plotted. Referring to the figure, “m2” is not near the center (◯) of the Smith chart, and the impedance is shifted.

FIG. 13 is a Smith chart displaying stability circles satisfying the above expression (3) in the circuit of FIG. In the figure, a thick solid line is the outer periphery of the stability circle. The measurement point “m3” is a point where the value of S ₁₁ at a frequency of 16 GHz is plotted. The distance from the center (○) of the Smith chart of “m3” is about 3. Thus, since “m3” is not within a circle having a radius of 1, the high-frequency circuit 1 is stable, and the stability of the high-frequency circuit 1 in the 16 GHz band is improved.

  In summary, from FIG. 11 to FIG. 13, if the inserted chip resistor 17 is regarded as a lumped constant circuit, short-circuiting in the 16 GHz band is eased, but impedance matching cannot be achieved at a desired frequency of 10 GHz.

  Next, consider the case where the chip resistor 17 is regarded as a distributed constant circuit in the impedance matching calculation, that is, the case where the chip resistor 17 is replaced with the equivalent circuit shown in FIG.

  FIG. 14 is a flowchart showing a method for designing a high-frequency circuit when the chip resistor 17 is regarded as a distributed constant circuit. Referring to the figure, the designer first inputs various parameters when the chip resistor 17 is regarded as a distributed constant circuit to simulation software such as ADS used in FIGS. 5 to 13 (step S1).

  In the equivalent circuit shown in FIG. 3, the capacitor component and the inductance component are determined by the physical shape of the chip resistor 17 (chip size and electrode size) and the frequency. For example, at 10 GHz, the value of the capacitor component is 0.1 (pF), and the value of the inductance component is 0.01 (nH). The values of other parameters are the same as those in FIGS.

  Then, the designer inputs a candidate resistance value of the chip resistor 17 (step S2). The designer adjusts the impedance of the open stub 16 by outputting the S parameter and the Smith chart of the entire high-frequency circuit 1 and changing the length according to the result. In this way, the designer performs impedance matching at a desired frequency (10 GHz) (step S3).

  Next, the designer outputs a stability circle in a high frequency band (16 GHz) higher than a desired frequency, and determines the stability of the high frequency circuit 1 (step S4).

  The designer determines whether or not the high-frequency circuit 1 is stable in the high-frequency band from the simulation result (step S5).

  If the high frequency circuit 1 is not stable in the high frequency band (step S5: NO), the designer changes the candidate resistance value to be input, and returns to step S1. If impedance matching is achieved in the high-frequency circuit 1 and the high-frequency circuit 1 is stable (step S5: YES), the designer determines the candidate at that time as the resistance value of the chip resistor 17 and finishes the design. To do.

  15 to 17 are diagrams showing the results of designing the high-frequency circuit 1 by the design method shown in FIG.

FIG. 15 is a graph showing S parameters S ₁₁ and S ₂₁ calculated for each frequency in the circuit of FIG. Referring to the figure, in the figure, the measurement point “m1” is a point where the value of S _{11 in} the 10 GHz band is plotted. Referring to the figure, the gain of “m1” is sufficiently high. Further, similarly to the result shown in FIG. 11, the short-circuit property is relaxed in the 16 GHz band.

FIG. 16 is a Smith chart obtained by plotting the value of S ₁₁ of the high-frequency circuit 1 obtained from the circuit of FIG. In the figure, the measurement point “m2” is a point where the value of S ₁₁ at a frequency of 10 GHz, which is a desired frequency, is plotted. Referring to the figure, “m2” is near the center of the Smith chart, and impedance matching is taken.

FIG. 17 is a Smith chart displaying a stability chart satisfying the above expression (3) in the circuit of FIG. The measurement point “m3” is a point where the value of S ₁₁ at a frequency of 16 GHz is plotted. Referring to the figure, the distance from the center (○) of the Smith chart of “m3” is about 2. Thus, since “m3” is not in the circle with the radius 1, the circuit is stable even in the 16 GHz band.

  In summary, from FIG. 15 to FIG. 17, the inserted chip resistor 17 is regarded as a distributed constant circuit, so that the short circuit in the 16 GHz band is alleviated and the high-frequency circuit 1 is stabilized even at a desired frequency (16 GHz). .

  On the other hand, if the circuit of FIG. 2 is configured with components that are regarded as lumped constants, not only the number of components increases, but those components become visible as distributed constants in the high frequency band. For this reason, in the high frequency band, the equivalent circuit of FIG. 3 is different from the circuit shown in FIG. 3, and desired characteristics cannot be obtained.

  Note that all or part of the flowchart shown in FIG. 14 can also be realized by executing a computer program.

  In the present embodiment, the impedance matching is performed and then the stability of the high-frequency circuit 1 is determined. However, the impedance matching may be performed after the stability of the high-frequency circuit 1 is determined.

  In this embodiment, the open stub 16 is used because it is easy to change the impedance value only by adjusting the length. However, if the impedance can be adjusted, a short stub may be used instead of the open stub 16. Of course it is good.

  In the present embodiment, the chip resistor 17 is inserted at the base of the open stub 16. However, if the chip resistor 17 is connected in parallel to the high-frequency amplifier circuit 13, A chip resistor 17 may be connected.

  In the present embodiment, since it is easy to calculate the reactance value from the physical shape and the frequency as the chip resistor 17, an SMT component is used. However, if the reactance value corresponding to the frequency can be calculated, A resistor other than the SMT component may be used.

  The high frequency amplifier circuit 13 of the present embodiment corresponds to the electronic circuit of the present invention.

  As described above, according to the present invention, since the resistor inserted in parallel with the electronic circuit is regarded as a distributed constant circuit, impedance matching can be appropriately performed in the high-frequency circuit, so that the stability of the high-frequency circuit can be improved. . Further, since it is not necessary to insert components such as coils and capacitors, the number of components can be reduced.

DESCRIPTION OF SYMBOLS 1 High frequency circuit 11 Input terminal 12 Distributed constant line 13 High frequency amplifier circuit 14 Output matching circuit 15 Output terminal 16 Open stub 17 Chip resistance

Claims (5)

In a high-frequency circuit having an electronic circuit, a stub connected in parallel to the electronic circuit, and a resistor connected in parallel to the electronic circuit, the resistance is replaced with an equivalent circuit that is a distributed constant circuit,
The impedance value of the stub is such that the impedance matching of the high-frequency circuit is performed at a first frequency used in the high-frequency circuit, and the high-frequency circuit is stabilized at a second frequency that should be stabilized. A method for designing a high-frequency circuit, wherein a resistance value of the equivalent circuit is set. In setting the impedance value and the resistance value,
Set the resistance value candidates,
After setting the impedance so that impedance matching of the high-frequency circuit can be taken at the first frequency, determine whether the high-frequency circuit is stable at the second frequency,
The method for setting a high-frequency circuit according to claim 1, wherein if the high-frequency circuit is stable, the candidate is set as a resistance value of the equivalent circuit.   The high-frequency circuit design method according to claim 2, wherein the stub is an open stub, and the impedance value is set by adjusting a length of the open stub. The resistor is an SMT component,
The high-frequency circuit design method according to claim 1, wherein the reactance value of the equivalent circuit is a value determined by a physical shape of the SMT component and a frequency. Electronic circuit,
An impedance value is set so that impedance matching of the high-frequency circuit is performed at a first frequency used in the high-frequency circuit, and a stub connected in parallel to the electronic circuit;
A resistance value is set so that the high-frequency circuit is stabilized at a second frequency at which the high-frequency circuit is to be stabilized, and a resistor connected in parallel to the electronic circuit;
A high frequency circuit.

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