JP2013183351A - Directional coupler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a directional coupler in which a device area or an insertion loss can be prevented from being increased, while suppressing reduction in a coupling amount of coupling characteristics in spite of a configuration where compensation circuits and attenuators are provided.SOLUTION: A directional coupler 1 comprises a main line 2, a sub line 3, compensation circuits 6A and 6B and attenuators 5A and 5B. The compensation circuit 6A and 6B are connected to the sub line and compensate for a frequency deviation of a coupling amount between a coupling port and a signal input port. The attenuators 5A and 5B are connected between the sub line 3 and the compensation circuits 6A and 6B respectively and attenuate a signal to be passed. The compensation circuits 6A and 6B include resistors R connected in series between a signal line and a ground, and reactance circuits 4A and 4B connected between the resistors R and the attenuators 5A and 5B respectively.

Description

  The present invention relates to a directional coupler used for applications such as high-frequency signal measurement, and more particularly to a transmission line type directional coupler.

  Conventionally, directional couplers are used for applications such as high-frequency signal measurement.

  FIG. 8A is a general block diagram of an RF (Radio Frequency) transmission circuit 100 such as a mobile phone device. The RF transmission circuit 100 includes an antenna 111, a directional coupler 120A, a transmission power amplifier 113, a modulation circuit 112, and a detection circuit 114. The directional coupler 120 </ b> A is a transmission line type, and includes a main line 121 and a coupled line (sub line) 122. The main line 121 is connected between the antenna 111 and the transmission power amplifier 113. The detection circuit 114 is connected to the sub line 122 of the directional coupler 120A, and controls the transmission power amplifier 113 based on a signal from the sub line 122 coupled to the main line 121.

  FIG. 8B is an equivalent circuit diagram according to the embodiment of the directional coupler 120A. Here, the directional coupler 120A is an ideal circuit in which the magnetic coupling coefficient Km of the mutual inductance generated between the main line 121 and the sub line 122 and the electric field coupling coefficient Kc of the coupling capacitance are 1. . The main line 121 and the sub line 122 are electrically coupled to each other by distributed capacitance (coupling capacitance) between both lines, and are magnetically coupled to each other by mutual inductance. Both ends of the main line 121 are connected to a signal input port RFin and a signal output port RFout. Both ends of the sub line 122 are connected to the coupling port CPL and the isolation port ISO. The signal input port RFin is connected to a transmission power amplifier. The signal output port RFout is connected to an antenna. The coupling port CPL is connected to a detection circuit. The isolation port ISO is connected to a termination load.

  In the directional coupler 120A, when the signal S1 is input from the signal input port RFin, the signal S2 is transmitted in the direction of the coupling port CPL and the signal S3 is transmitted in the direction of the isolation port ISO by the sub-line 122 due to electric field coupling. Propagate. Further, due to the magnetic field coupling, the signals S4 and S5 are propagated from the isolation port ISO to the coupling port CPL in a closed loop of the sub line 122 and the ground. The signals S2 and S4 flowing through the coupling port CPL have the same phase, and a signal obtained by adding the powers of the signals S2 and S4 is output from the coupling port CPL. On the other hand, the signals S3 and S5 flowing through the isolation port ISO are out of phase, and the power of the signals S3 and S5 cancel each other out at the isolation port ISO. Therefore, it is possible to detect the output power of the RF transmission circuit 100 from the output of the coupling port CPL.

  Normally, a termination resistor is connected to the isolation port ISO so that a reflected signal from the antenna is released to the ground. However, in recent years, a detection circuit may be provided in order to detect reflection from the antenna. In that case, the function of each port (signal input port and signal output port, coupling port and isolation port) acts on the reflected signal from the antenna in reverse.

  In recent years, there has been a growing demand for using directional couplers in a wide band. For example, a single directional coupler or detector circuit is required to correspond to a signal of 700 MHz to 900 MHz used in a mobile phone system.

  FIG. 8C is a diagram showing output characteristics in the directional coupler 120A. The coupling characteristic shown in the figure indicates the frequency characteristic of the coupling amount between the signal input port RFin and the coupling port CPL. The isolation characteristic refers to a frequency characteristic of a coupling amount (isolation) between the signal input port RFin and the isolation port ISO. The insertion loss characteristic refers to the frequency characteristic of the coupling amount (insertion loss) between the signal input port RFin and the signal output port RFout. The reflection loss characteristic refers to the frequency characteristic of the input / output coupling amount (reflection loss) at the signal input port RFin. Directional characteristics refer to frequency characteristics corresponding to the difference between isolation characteristics and coupling characteristics.

  This directional coupler 120A has a coupling characteristic in which the coupling amount changes at a constant rate from 700 MHz to 900 MHz due to the frequency characteristics of electromagnetic coupling (for example, +6 dB / Oct.). Specifically, the coupling characteristic has a frequency deviation of about 2.1 dB between 700 MHz and 900 MHz. Thus, when there is a frequency deviation in the coupling amount, several types of directional couplers 120A with different available frequency bands are prepared, and detection is performed according to the frequency band of the mobile phone system. There is a case where the types of circuits need to be different and cannot be handled by a single directional coupler.

Therefore, in order to make the directional coupler having a single configuration compatible with a wide band, a compensation circuit for frequency characteristics may be connected to the coupling port or the isolation port (see, for example, Patent Document 1).
FIG. 9A is an equivalent circuit diagram according to the embodiment of the directional coupler to which the compensation circuit is connected. In the directional coupler 120B, the compensation circuit 123A is connected to the coupling port CPL, and the compensation circuit 123B is also connected to the isolation port ISO. Each of the compensation circuits 123A and 123B includes a capacitance connected between the signal line and the ground. The compensation circuits 123A and 123B have an attenuation characteristic in which the attenuation amount changes at a constant rate (for example, −6 dB / Oct.) At a cutoff frequency or higher. By providing such compensation circuits 123A and 123B, coupling characteristics and isolation characteristics can be flattened in a specific frequency band (700 MHz to 900 MHz). However, by connecting the compensation circuits 123A and 123B, signal reflection (mismatch) between the compensation circuits 123A and 123B and the sub line 122 increases depending on the frequency. Therefore, in the directional coupler 120B, attenuators (attenuators) 124A and 124B are connected between the compensation circuits 123A and 123B and the sub line 122. The attenuators 124A and 124B have, for example, a pass characteristic of −10 dB. By providing the attenuators 124A and 124B, the influence of signal reflection (mismatch) generated between the compensation circuits 123A and 123B and the sub line 122 can be reduced.

  FIG. 9B is a diagram illustrating output characteristics of the directional coupler 120B. In this directional coupler 120B, in the coupling characteristics, the frequency deviation of the coupling amount between 700 MHz and 900 MHz is about 1.0 dB or less. However, since the signals are attenuated by the attenuators 124A and 124B, the coupling amount of the coupling characteristic is reduced by about 15 dB to about 36 dB compared with the case where the attenuator shown in FIG. 8C is not provided.

JP 2009-044303 A

  In the directional coupler 120B described above, the frequency deviation of the coupling amount in the coupling characteristic can be reduced. However, the coupling amount itself in the coupling characteristic is lowered, and the coupling amount (for example, for accurate detection in the detection circuit) -25 dB) may not be ensured. In order to prevent this, it is necessary to increase the amount of coupling itself of the coupling characteristics by increasing the mutual inductance and the coupling capacitance between the main line and the sub line.

  FIG. 10A is an equivalent circuit diagram according to the embodiment of the directional coupler 120C in which the coupling amount between the main line and the sub line is increased. In this directional coupler 120C, the reactance values of the main line 121 and the sub line 122 are five times that of the directional coupler 120B described above. FIG. 10B shows the output characteristics of the directional coupler 120C. In this directional coupler 120C, the frequency deviation of the coupling amount between 700 MHz and 900 MHz in the coupling characteristics is about 1.0 dB or less. Further, the coupling amount of the coupling characteristic is about 23 dB. As described above, by increasing the reactance values of the main line and the sub-line, it is possible to increase the coupling amount while reducing the frequency deviation in the coupling characteristics.

  However, in the directional coupler 120C, since the coupling amount between the main line 121 and the sub line 122 is greatly increased, the insertion loss characteristic is deteriorated (insertion loss is increased). Moreover, in order to realize a reactance value for obtaining such a coupling amount, it is necessary to increase the reactance value by five times as described above, and as a result, the device area occupied by the main line and the sub-line is greatly increased. Resulting in.

  Accordingly, an object of the present invention is to provide a directional coupler capable of preventing an increase in device area and insertion loss while suppressing a decrease in coupling amount in coupling characteristics even in a configuration in which a compensation circuit and an attenuator are provided. Is to realize.

  The directional coupler according to the present invention includes a main line, a sub line, a compensation circuit, and an attenuator. The main line is connected between the signal input port and the signal output port. The sub line is connected between the coupling port and the isolation port, and is coupled to the main line by a coupling capacitance and a mutual inductance. The compensation circuit is connected to the sub line and compensates for the frequency deviation of the coupling amount between the coupling port and the signal input port. The attenuator is connected between the sub line and the compensation circuit, and attenuates the signal passing therethrough. Here, the compensation circuit includes a resistance unit connected between the coupling port and the ground, and a reactance unit connected between the resistance unit and the attenuator.

  In this configuration, by providing the reactance unit in the compensation circuit, it is possible to compensate for the frequency deviation of the coupling amount between the signal input port and the coupling port. Further, by providing a lossy resistor in the compensation circuit, signal reflection (mismatch) between the compensation circuit and the attenuator can be reduced. Thereby, even if it uses an attenuator with small attenuation amount, the influence of the reflection (mismatch) in a compensation circuit can be suppressed. Therefore, the reactance values of the main line and the sub line necessary for securing the coupling amount are reduced, and an increase in device area and insertion loss can be prevented.

  In the above-described directional coupler, the reactance unit preferably includes a resonance circuit.

  In the directional coupler described above, it is preferable that the reactance unit includes an adjustment reactance for adjusting the resonance Q of the resonance circuit.

  In the directional coupler described above, the resonant circuit includes a first reactance having a first end connected to the signal line, and a second reactance connected between the second end of the first reactance and the ground. A first reactance is connected between the second end of the first reactance and the ground, and the resistance portion is between the second end of the adjusting reactance and the ground. It is preferable that it is connected to.

  In the directional coupler described above, the first reactance may be a capacitor, the second reactance may be an inductor, and the adjustment reactance may be a capacitor.

  In the above-described directional coupler, it is preferable that the main line, the sub line, the compensation circuit, and the attenuator are formed by a thin film process.

  In the directional coupler described above, it is preferable that the main line, the sub line, the compensation circuit, and the attenuator include a semi-insulating substrate formed on the same main surface.

  According to the present invention, by providing the directional coupler with a compensation circuit including a resistance unit, the signal reflection (mismatch) in the compensation circuit is reduced while compensating for the frequency deviation of the coupling amount in the coupling characteristics. it can. Thereby, even if the attenuation amount of the attenuator for suppressing the reflection (mismatch) of the signal in the compensation circuit is small, the influence of the reflection (mismatch) in the compensation circuit can be suppressed. Therefore, the reactance values of the main line and the sub line necessary for securing the coupling amount are reduced, and an increase in device area and insertion loss can be prevented.

It is a schematic diagram of the directional coupler which concerns on the 1st Embodiment of this invention. It is a top view of the directional coupler which concerns on the Example of this invention. It is an equivalent circuit schematic of the directional coupler which concerns on the Example of this invention. It is an output characteristic figure of the directional coupler which concerns on the Example of this invention. It is an equivalent circuit diagram of the compensation circuit which concerns on the Example of this invention, and the compensation circuit which concerns on a comparison form. It is an output characteristic of the compensation circuit which concerns on the Example of this invention, and the compensation circuit which concerns on a conventional structure. It is a figure explaining the compensation circuit which concerns on other embodiment of this invention. It is a figure explaining the example of a conventional structure of a directional coupler. It is a figure explaining the example of a conventional structure of a directional coupler. It is a figure explaining the example of a conventional structure of a directional coupler.

  Hereinafter, a schematic configuration and operation of the directional coupler according to the embodiment of the present invention will be described.

  FIG. 1 is a schematic diagram of a directional coupler 1 according to an embodiment of the present invention.

  The directional coupler 1 includes a signal input port RFin, a signal output port RFout, a coupling port CPL, and an isolation port ISO as external connection terminals. When this directional coupler 1 is used in an RF transmission circuit, the signal input port RFin is connected to a transmission power amplifier. The signal output port RFout is connected to the antenna, the coupling port CPL is connected to the detection circuit or the termination resistor, and the isolation port ISO is connected to the termination load or the detection circuit.

  The directional coupler 1 includes a main line 2, a coupled line (sub line) 3, attenuators 5A and 5B, and compensation circuits 6A and 6B as internal elements. The compensation circuits 6A and 6B include reactance circuits 4A and 4B and a resistor R. The resistor R corresponds to the resistor unit in this embodiment. The reactance circuits 4A and 4B correspond to the reactance unit in the present embodiment.

The main line 2 is connected between the signal input port RFin and the signal output port RFout. The sub line 3 is capacitively coupled to the main line 2 by a distributed capacitance (coupling capacity) between the sub line 3 and the main line 2 and is magnetically coupled to the main line 2 by a mutual inductance with the main line 2.
The reactance circuits 4A and 4B and the resistor R constitute compensation circuits 6A and 6B having losses. The reactance circuit 4A is connected between the coupling port CPL and the first end of the sub line 3. The reactance circuit 4A is set to a predetermined attenuation characteristic. The attenuation characteristic of the reactance circuit 4A is set so as to compensate for the frequency deviation of the coupling amount between the signal input port RFin and the coupling port CPL in a predetermined frequency band. The reactance circuit 4B is connected between the isolation port ISO and the second end of the sub line 3. The reactance circuit 4B has a predetermined attenuation characteristic set. The attenuation characteristic of the reactance circuit 4B is set so as to compensate for the frequency deviation of the coupling amount between the signal output port RFout and the isolation port ISO in a predetermined frequency band.

  The attenuator 5A is connected between the reactance circuit 4A and the first end of the sub line 3. The attenuator 5A has a predetermined attenuation, attenuates the reflected signal from the compensation circuit 6A, and reduces the influence of mismatch of the compensation circuit 6A. The attenuator 5B is connected between the reactance circuit 4B and the second end of the sub line 3. The attenuator 5B has a predetermined attenuation amount, attenuates the reflected signal from the compensation circuit 6B, and reduces the influence of mismatch of the compensation circuit 6B.

  The resistor R that constitutes the compensation circuit 6A together with the reactance circuit 4A is connected between the reactance circuit 4A and the ground potential, and increases the insertion loss of the compensation circuit 6A and decreases the reflection loss of the compensation circuit 6A. That is, the reflected signal of the compensation circuit 6A is reduced. The resistor R that constitutes the compensation circuit 6B together with the reactance circuit 4B is connected between the reactance circuit 4B and the ground potential, and increases the insertion loss of the compensation circuit 6B and decreases the reflection loss of the compensation circuit 6B. That is, the reflected signal of the compensation circuit 6B is reduced.

  In the directional coupler 1 having such a configuration, since the reflections of the compensation circuits 6A and 6B are small, it is possible to employ the attenuators 5A and 5B having a relatively small attenuation. For this reason, the amount of coupling between the signal input port RFin and the coupling port CPL and the amount of coupling between the signal output port RFout and the isolation port ISO are less affected by the attenuators 5A and 5B, and are much reduced. There is no. Therefore, it is not necessary to significantly increase the reactance values of the main line 2 and the sub line 3, and it is possible to prevent the device area and insertion loss of the directional coupler 1 from becoming excessive.

<Example>
Next, examples of the directional coupler according to this embodiment will be described.

  FIG. 2 is a plan view of the directional coupler 11 according to the embodiment of the present invention.

  The directional coupler 11 includes a semi-insulating GaAs substrate 10A and a dielectric film 10B.

On the main surface of the GaAs substrate 10A shown in FIG. 2 (A), resistors R1A, R2A, R3A, R4A, R1B, R2B, R3B, R4B, and electrodes composed of a main line 12, a sub line 13, and a high resistance line, and electrodes 17A-17D, 18A, 18B, 19A, 19B, 20A, 20B, 21A, 21B, 22A, 22B, 23A, 23B, 24A, 24B are formed.
2B, electrodes 31A, 31B, 32A, 32B, 33A, 33B, 34A, and 34B and inductors L1A and L1B made of line electrodes are formed on the main surface of the dielectric film 10B shown in FIG. Has been.

  The main line 12 and the sub line 13 are formed so that the longitudinal directions of the main line 12 and the sub line 13 are in the same direction (left and right direction in FIG. 2A) and parallel to each other, and mutual inductance and distribution acting between each other. Coupled with capacity.

Here, the electrode 17C constitutes a signal input port RFin terminal. The electrode 17D constitutes a signal output port RFout terminal.
The electrode 17A constitutes a coupling port CPL terminal. The electrode 17B constitutes an isolation port ISO terminal.

  The electrode 18A constitutes a ground GND terminal. The electrode 18B also constitutes a ground GND terminal.

The sub line 13 and the coupling port CPL are connected in order from the sub line 13 side via a resistor R1A, an electrode 19A, a resistor R3A, and an electrode 20A. Further, the sub line 13 and the isolation port ISO are connected in order from the sub line 13 side via a resistor R1B, an electrode 19B, a resistor R3B, and an electrode 20B.
An electrode 19A corresponding to a connection point between the resistor R1A and the resistor R3A is connected to the ground GND via the resistor R2A. An electrode 19B, which is a connection point between the resistor R1B and the resistor R3B, is connected to the ground GND through the resistor R2B.
An electrode 20A, which is a connection point between the resistor R3A and the electrode 17A (coupling port CPL), is connected to the electrode 32A via a capacitor C1A formed by the electrode 21A and the electrode 31A. The electrode 32A is connected to the electrode 18A (ground GND) through the capacitor C2A, the electrode 23A, and the resistor R4A formed by the electrode 33A and the electrode 22A in this order, and the electrode 33A, the inductor L1A, the electrode 34A, and the electrode 24A in order. )It is connected to the.
An electrode 20B, which is a connection point between the resistor R3B and the electrode 17B (isolation port ISO), is connected to the electrode 32B via a capacitor C1B formed by the electrode 21B and the electrode 31B. The electrode 32B is connected to the electrode 18B (ground GND) via the capacitor C2B, the electrode 23B, and the resistor R4B formed by the electrode 33B and the electrode 22B in this order, and the electrode 33B, the inductor L1B, the electrode 34B, and the electrode 24B. )It is connected to the.

  The directional coupler 11 is formed by a semiconductor thin film process using a wafer-like GaAs substrate 10A. In the semiconductor thin film process, after an electrode material is formed on a semiconductor material by vapor deposition, sputtering, plating, or the like, a resist film is formed by a photolithography process, and unnecessary electrode material is removed by etching. Alternatively, after a resist film pattern is first formed by a photolithography process, an electrode material is deposited on a portion other than the resist film pattern by vapor deposition, sputtering, plating, or the like, and finally the resist film is peeled off (lifted off). An electrode pattern is formed.

  More specifically, first, high resistance lines to be resistors R1A, R1B, R2A, R2B, R3A, R3B, R4A, and R4B are formed at a time on the main surface of the wafer-like GaAs substrate 10A. Next, on the main surface of the wafer-like GaAs substrate 10A, the main line 12, the sub line 13, the electrodes 17A to 17D, 18A, 18B, 19A, 19B, 20A, 20B, 21A, 21B, 22A, 22B, 23A, 23B, 24A, and 24B are formed at a time. Next, a dielectric film 10B is formed on the main surface of the wafer-like GaAs substrate 10A. Next, the dielectric film 10B is subjected to etching, electrode filling treatment, and the like to form a via electrode. Next, line electrodes to be electrodes 31A, 31B, 32A, 32B, 33A, 33B, 34A, 34B and inductors L1A, L1B are formed at a time on the main surface of the dielectric film 10B. A plurality of directional couplers 11 are manufactured at a time by dividing the wafer.

  Thus, if the directional coupler 11 is manufactured using the semiconductor thin film process, the shape accuracy of each electrode can be made extremely high, and the output characteristics of the coupling amount and the isolation that are extremely small as −30 dB to −60 dB with respect to the input power Even so, it can be realized stably. Therefore, the directional coupler 11 can be realized with a high yield. Further, when using a semiconductor thin film process, if a general Si substrate is used, the loss of the substrate is large and the insertion loss of the directional coupler 11 is increased. However, by using a semi-insulating substrate such as a GaAs substrate. Insertion loss can be reduced. Further, not only the directional coupler but also other active elements can be mixedly mounted on the semi-insulating substrate, and the device can be reduced in size and price.

  FIG. 3 is an equivalent circuit diagram of the directional coupler 11.

  In the directional coupler 11, the main line 12 and the sub line 13 each have an inductance of 1.6 nH. The magnetic field coupling coefficient Km between the main line 12 and the sub line 13 is 1, and the mutual inductance between the main line 12 and the sub line 13 is 1.6 nH. The main line 12 and the sub line 13 have an electric field coupling coefficient Kc of 1 and a distributed capacity of 0.32 pF × 2.

The resistors R1A, R2A, R3A constitute an attenuator 25A. The resistance value of the resistor R1A and the resistor R3A is 16.7Ω. The resistance value of the resistor R2A is 66.7Ω. The attenuator 25A is connected between the sub line 13 and the coupling port CPL. The resistor R1A and the resistor R3A are connected in series between the sub line 13 and the coupling port CPL. The resistor R2A is connected between the connection point of the resistors R1A and R3A and the ground potential. Thus, the attenuator 25A is configured and functions as a -6 dB attenuator here.
The resistors R1B, R2B, and R3B constitute an attenuator 25B. The resistance value of the resistor R1B and the resistor R3B is 16.7Ω. The resistance value of the resistor R2B is 66.7Ω. The attenuator 25B is connected between the sub line 13 and the isolation port ISO. The resistor R1B and the resistor R3B are connected in series between the sub line 13 and the isolation port ISO. The resistor R2B is connected between the connection point of the resistors R1B and R3B and the ground potential. Thus, the attenuator 25B is configured and functions as an attenuator of −6 dB here.

Capacitances C1A and C2A and inductance L1A constitute reactance circuit 24A. The reactance circuit 24A is connected between the connection point between the attenuator 25A and the coupling port CPL and the ground potential. The capacitance C1A and the inductor L1A constitute an LC series resonance circuit. The capacitance C1A is connected to a connection point between the attenuator 25A and the coupling port CPL, and the inductor L1A is between the capacitance C1A and the ground potential. It is connected to the. The capacitance C2A is connected to a connection point between the capacitance C1A and the inductance L1A. The resistor R4A is connected between the capacitance C2A and the ground potential. The capacitance C2A is provided to adjust the resonance Q of the LC series resonance circuit, and corresponds to the adjustment reactance in this embodiment.
Capacitances C1B and C2B and inductance L1B constitute reactance circuit 24B. The reactance circuit 24B is connected between the connection point between the attenuator 25B and the isolation port ISO and the ground potential. The capacitance C1B and the inductor L1B constitute an LC series resonance circuit. The capacitance C1B is connected to the connection point between the attenuator 25B and the isolation port ISO, and the inductor L1B is between the capacitance C1B and the ground potential. It is connected to the. Capacitance C2B is connected to a connection point between capacitance C1B and inductance L1B. The resistor R4B is connected between the capacitance C2B and the ground potential. The capacitance C2B is provided to adjust the resonance Q of the LC series resonance circuit, and corresponds to the adjustment reactance in this embodiment.

  Here, the reactance circuits 24A and 24B constitute a so-called band rejection filter, and the resonance frequency of the band rejection filter is configured to be slightly higher than the frequency band to be used (for example, 700 MHz to 900 MHz). Has been. As a result, this band rejection filter operates capacitively.

  FIG. 4 is a diagram illustrating the output characteristics of the directional coupler 11 according to the embodiment of the present invention. Note that the coupling characteristics shown in the figure indicate the frequency characteristics of the coupling amount between the signal input port RFin and the coupling port CPL. The isolation characteristic indicates the frequency characteristic of the coupling amount (isolation) between the signal input port RFin and the isolation port ISO. The insertion loss characteristic indicates the frequency characteristic of the coupling amount (insertion loss) between the signal input port RFin and the signal output port RFout. The reflection loss characteristic indicates the frequency characteristic of the input / output coupling amount (reflection loss) at the signal input port RFin. Directional characteristics refer to frequency characteristics corresponding to the difference between isolation characteristics and coupling characteristics.

  In this directional coupler 11, the coupling amount (coupling characteristic) between the signal input port RFin and the coupling port CPL is stable from 700 MHz to 900 MHz, and the frequency deviation is 1 dB or less. With such a stable coupling characteristic with a small frequency deviation, the directional coupler 11 can be used as it is in a 700 MHz band mobile phone system or an 800 MHz band mobile phone system. Further, the coupling characteristic between the signal input port RFin and the coupling port CPL is greater than about −24 dB from 700 MHz to 900 MHz. This amount of coupling is comparable to the ideal amount of coupling shown in FIGS. 8C and 10B, and is sufficiently larger than the conventional example shown in FIG. 9B. Amount. Therefore, in this directional coupler 11, it is not necessary to increase the reactance values of the main line 12 and the sub-line 13 in order to ensure the amount of coupling, and it is possible to prevent the device area and insertion loss from becoming excessive.

  As shown in FIG. 8C, the original coupling amount between the signal input port RFin and the coupling port CPL has a frequency deviation that gradually increases from 700 MHz to 900 MHz. In order to compensate for such inherent coupling characteristics, here, a band-stop filter is configured as the reactance circuits 24A and 24B, the resonance frequency thereof is set to 900 MHz or more, and the frequency band in which the band-stop filter functions capacitively, That is, a frequency band in which the passing amount from 700 MHz to 900 MHz is gradually used is used.

Next, the frequency characteristics of the compensation circuit alone will be specifically described.
FIG. 5A is an equivalent circuit diagram of the compensation circuit according to this embodiment, and FIG. 5B is an equivalent circuit diagram of the compensation circuit according to the conventional example. FIG. 6A is a diagram illustrating the insertion loss characteristics of the compensation circuit according to the present embodiment and the compensation circuit according to the conventional example, and FIG. 6B illustrates the compensation circuit according to the present embodiment. It is a figure which shows the reflective loss characteristic in single unit with the compensation circuit which concerns on a prior art example.

  As shown in FIG. 6B, the amount of reflection in this embodiment is smaller than the amount of reflection in the conventional example in the entire band including 700 MHz to 900 MHz. On the other hand, from FIG. 6A, the passing amount in the present embodiment is larger than the passing amount in the conventional example in the entire band including 700 MHz to 900 MHz. This is because the compensation circuit of the present embodiment is configured not only by a single reactance component but also by a resistor having a loss and a reactance component. The characteristic shown in FIG. 6 is a result of setting the resistance value and the reactance value in the compensation circuit so that an appropriate passage amount difference is obtained in a desired frequency band (700 MHz to 900 MHz). Thus, the frequency deviation of the coupling amount is compensated.

  Therefore, by configuring a compensation circuit having a resistance as shown in the present embodiment and this example and compensating the coupling characteristics of the directional coupler, reflection (mismatch) in the compensation circuit is suppressed. Can do. And it becomes possible to employ | adopt a structure with small attenuation amount as an attenuator connected between a compensation circuit and a subline. And by using an attenuator with a small attenuation amount, it becomes possible to suppress the reactance constituted by the main line and the sub line, and as a result, it is possible to reduce the device area and the insertion loss of the directional coupler. Can be realized. In addition, in this embodiment, since the passing amount of the compensation circuit is larger than that of the conventional example, it is possible to suppress a decrease in the coupling amount in the entire directional coupler, which also reduces the device area and directional coupling. It is possible to reduce the insertion loss of the device.

<< Other Embodiments >>
Next, a directional coupler according to another embodiment of the present invention will be described.

  FIG. 7 is an equivalent circuit diagram showing a compensation circuit that can be provided in a directional coupler according to another embodiment.

  The compensation circuit 36A shown in FIG. 7A includes an LC series circuit and a resistor R connected in series between the signal path and the ground. This LC series circuit functions as a band rejection filter. Even with such a circuit configuration, the compensation circuit 36A can have a loss.

  The compensation circuit 46A shown in FIG. 7B includes an LC series circuit connected in series to the signal path, and a resistor R connected between the connection point of the LC series circuit and the coupling port and the ground. I have. This LC series circuit functions as a band pass filter. When configuring such a band-pass filter, the resonant frequency of the LC series circuit should be lower than the frequency band in which the directional coupler is used, as opposed to configuring the band-stop filter described above. Thus, the bandpass filter functions inductively. Thereby, even if it uses a band pass filter, the coupling | bonding characteristic of the main body in a directional coupler can be compensated. Further, by connecting the resistor R between the connection point between the LC series circuit and the coupling port and the ground, the compensation circuit 46A can have a loss.

  The compensation circuit 56A shown in FIG. 7C includes an LC parallel circuit connected in series to the signal path, and a resistor R connected between the connection point of the LC parallel circuit and the coupling port and the ground. I have. Even with such a circuit configuration, the coupling characteristics of the main body in the directional coupler can be compensated by appropriately adjusting the resonance frequency of the LC parallel circuit. Further, by connecting the resistor R between the connection point between the LC parallel circuit and the coupling port and the ground, the compensation circuit 56A can have a loss.

  The compensation circuit 66A shown in FIG. 7D includes an LC parallel circuit connected in series between the signal path and the ground, and a resistor R connected in series to the LC parallel circuit. This LC parallel circuit functions as a band pass filter. Even with such a circuit configuration, the coupling characteristics of the main body in the directional coupler can be compensated by appropriately adjusting the resonance frequency of the LC parallel circuit. Further, by connecting the resistor R in series with the LC parallel circuit, the compensation circuit 66A can have a loss.

  The compensation circuit 76A shown in FIG. 7E includes a capacitance C1 and a resistor R in series between the signal path and the ground. Even with such a circuit configuration, the coupling characteristic of the main body in the directional coupler can be compensated by appropriately adjusting the pass characteristic of the capacitance C1. Further, by connecting the resistor R between the capacitance C1 and the ground, the compensation circuit 76A can have a loss.

  A compensation circuit 86A shown in FIG. 7F includes an inductance L1 connected in series to the signal path, and a resistor R connected between a connection point between the inductance L1 and the coupling port CPL and the ground. ing. Even with such a circuit configuration, the coupling characteristic of the main body in the directional coupler can be compensated by appropriately adjusting the pass characteristic of the inductance L1. Further, by connecting the resistor R between the connection point of the inductance L1 and the coupling port CPL and the ground, the compensation circuit 86A can have a loss.

  Even with such a configuration of the compensation circuit, the directional coupler of the present invention can be preferably implemented.

  Although the present invention can be implemented as in the embodiments and examples described above, the scope of the present invention is not limited to the description of the above-described embodiments. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1,11 ... Directional coupler 2, 12 ... Main line 3, 13 ... Sub line 4A, 4B, 24A, 24B ... Reactance circuit 5A, 5B, 25A, 25B ... Attenuator 6A, 6B, 36A, 46A, 56A, 66A, 76A, 86A ... Compensation circuit 10A ... GaAs substrate 10B ... Dielectric film

Claims (8)

A main line connected between the signal input port and the signal output port;
A sub-line connected between the coupling port and the isolation port and coupled to the main line by a coupling capacitance and a mutual inductance;
A compensation circuit that is connected between the coupling port and the sub-line and compensates for a frequency deviation of the coupling amount between the coupling port and the signal input port;
An attenuator connected between the sub line and the compensation circuit to attenuate a signal passing therethrough;
With
The compensation circuit includes a resistance unit connected between the coupling port and a ground, and a reactance unit connected between the resistance unit and the attenuator.   The directional coupler according to claim 1, wherein the reactance unit includes a resonance circuit.   The directional coupler according to claim 2, wherein the reactance unit includes an adjustment reactance for adjusting a resonance Q of the resonance circuit.   The resonant circuit includes a first reactance having a first end connected to the signal line, and a second reactance connected between the second end of the first reactance and the ground, The adjustment reactance has a first end connected between the second end of the first reactance and the ground, and the resistor is connected between the second end of the adjustment reactance and the ground. The directional coupler according to claim 3.   The directional coupler according to claim 4, wherein the first reactance is a capacitor, the second reactance is an inductor, and the adjustment reactance is a capacitor. The compensation circuit is a first compensation circuit, and the attenuator is a first attenuator.
A second compensation circuit that is connected between the isolation port and the sub line and compensates for a frequency deviation of the coupling amount between the isolation port and the signal output port;
A second attenuator connected between the subline and the second compensation circuit for attenuating a passing signal;
With
The second compensation circuit includes a resistance unit connected between the isolation port and the ground, and a reactance unit connected between the resistance unit and the second attenuator. The directional coupler according to any one of claims 1 to 5.   The directional coupler according to claim 1, wherein a main part of the main line, the sub line, the compensation circuit, and the attenuator is formed by a thin film process.   The directional coupler according to claim 1, further comprising a semi-insulating substrate in which the main line, the sub line, the compensation circuit, and the attenuator are formed on the same main surface.

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