JP2012213108A - Detection circuit, detection method, and micro wave radio communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detection circuit and detection method capable of effectively extending a detectable range of the detection circuit without enlarging circuit scale.SOLUTION: A detection circuit at least comprising a side coupling directional coupler 16, inserted into the subsequent stage of an amplifier 15 on a main signal line, and a detector 18, detecting a signal partially separated by the side coupling directional coupler 16, is connected to, for example, a PIN diode (p-intrinsic-n Diode) 17 as a variable resistive element whose resistance value can be changed by a control signal, in the isolation port 13 side of the side coupling directional coupler 16. A high-frequency resistance value is increased by decreasing a value of current flowing in the PIN diode 17, when a power level of a main signal is high; and, on the other hand, the high-frequency resistance value as the variable resistive element is decreased by increasing the value of the current flowing in the PIN diode 17 when the power level of the main signal is low.

Description

  The present invention relates to a detection circuit, a detection method, and a microwave radio communication device, and more particularly, to a detection circuit, a detection method, and a microwave radio communication device when a microwave band is used.

  One factor that determines the control range of the transmission power control circuit of the microwave radio communication apparatus is the output range of the detection circuit. The practical detection possible range of the diode detector generally used in the transmission power control circuit in the microwave band is about 35 dB. In general, when the input level to the detector is high, the detection voltage becomes too high, and the reliability of the diode itself becomes a problem. On the other hand, when the input level to the detector is low, the detection voltage and the control unit Since the difference from the added noise is small, there is a problem that the detection accuracy cannot be maintained. For this reason, a detection range of about 35 dB is common.

  The detection circuit of the conventional microwave radio communication apparatus employs a circuit configuration as shown in FIG. FIG. 5 is a circuit diagram showing a circuit configuration of a detection circuit of a conventional microwave radio communication apparatus.

  As shown in FIG. 5, the conventional detection circuit includes an amplifier 25 for amplifying an input signal, a side-coupled directional coupler 26 for separating a part of the input signal on the main signal line on the monitor line, and on the monitor line. A detector 28 is provided for evaluating the separated signals and detecting the input signal on the main signal line.

  Here, the input side terminal on the main signal line of the side coupling type directional coupler 26 is input to the input port 21, the output side terminal on the main signal line is output to the output port 24, and the signal is sent to the detector 28 on the monitor line. A coupling terminal for drawing in is called a coupling port 22, and a load-side isolation terminal on the monitor line is called an isolation port 23.

  FIG. 6 shows the required detection characteristics required as a detectable range in the detector 28 of the detection circuit shown in FIG. FIG. 6 is a characteristic diagram showing the required detection characteristics of the detector 28 in the conventional detection circuit shown in FIG. In FIG. 6, +5 dBm to −30 dBm, which is a detection range in which there is no problem with the problem related to the detection range described above, is set as a practical detectable range of the detector 28. That is, the range from the detection voltage 0.003V when the input power is −30 dBm to the detection voltage 1.1V when the input power is +5 dBm is set as the required detection range.

  Here, it is assumed that the coupling amount of the side coupling type directional coupler 26 is 25 dB, and there is no loss of the input / output ports 21 and 24, the coupling port 22, and the isolation port 23 for simplification. Assuming the case under ideal conditions, as shown in FIG. 7, it becomes possible to detect the output power of the detection target signal in the range of +30 dBm to −5 dBm. FIG. 7 is a characteristic diagram showing ideal detection characteristics of the detector 28 in the conventional detection circuit shown in FIG.

  As a method for expanding the detectable range of the detection circuit, Japanese Patent Application Laid-Open No. 2001-189667 “Transmission Power Control Circuit and Transmission Power Control Method” of Patent Document 1 and Japanese Patent Application Laid-Open No. 2005-252847 “Variable Power”. As disclosed in “Distribution Method, Variable Power Divider and Transmission Power Control Circuit”, a method of changing the distribution ratio of the power distribution circuit between the amplifier and the output terminal, that is, a subsequent stage of the amplifier 25 of FIG. There is a method of changing the degree of coupling of the side coupling type directional coupler 26 inserted into the.

  The methods described in Patent Documents 1 and 2 change the distribution ratio of the power distribution circuit for the problem that the detection accuracy cannot be maintained because the detection voltage level becomes low at the time of low level output. In other words, at the time of low level output, the distribution ratio, that is, the degree of coupling to the detector is increased. Even at low level output, the input power to the detector can be increased, thereby expanding the dynamic range of the detector and obtaining a sufficient detection voltage at the detector. .

Japanese Patent Laid-Open No. 2001-189667 (page 5-7) Japanese Patent Laying-Open No. 2005-252847 (page 5-7)

  However, the conventional techniques as described above have the following problems. In the technique of Patent Document 1, the resistance value of the variable resistor or the capacitance value of the variable capacitance element inserted between the coupling port and the detector is changed in order to switch the power distribution ratio. Therefore, the change in the input impedance of the power distribution circuit increases with a change in the resistance value of the variable resistor or the capacitance value of the variable capacitance element, which has a problem of adversely affecting the main signal.

  In the technique of Patent Document 2, it is necessary to provide various circuit configurations for synthesis by shifting the phase on the detector side, which increases the circuit scale, not only in terms of space but also in terms of cost. There is a problem.

(Object of the present invention)
The present invention has been made in view of such problems, and a detection circuit, a detection method, and a microwave radio communication apparatus that can effectively expand the detection possible range of a detection circuit without increasing the circuit scale. The purpose is to provide.

  In order to solve the above-described problems, the detection circuit, the detection method, and the microwave radio communication apparatus according to the present invention mainly adopt the following characteristic configuration.

  (1) A detection circuit according to the present invention includes a directional coupler inserted to separate a part of the main signal on a main line that propagates the main signal in the microwave band, and a part of the directional coupler by the directional coupler. A detection circuit for detecting the main signal, wherein a resistance value can be changed by a control signal on the isolation port side of the directional coupler. A variable resistance element is connected as a load.

  (2) The detection method according to the present invention includes a directional coupler inserted to separate a part of the main signal on a main line that propagates the main signal in the microwave band, and a partial separation by the directional coupler. A detector that detects the detected signal, and a variable resistance element that is connected to the isolation port side of the directional coupler as a load and can change a resistance value by a control signal, In the detection method for performing detection, when the power level of the main signal input to the directional coupler is higher than a predetermined high power threshold, the resistance value of the variable resistance element is increased, When the power level of the main signal is lower than a predetermined low power threshold, the resistance value of the variable resistance element is lowered.

  (3) A microwave radio communication apparatus according to the present invention uses at least the detection circuit described in (1) as a detection circuit that detects a signal in a microwave radio communication apparatus that transmits and receives a radio signal in a microwave band. It is characterized by that.

  According to the detection circuit, the detection method, and the microwave radio communication apparatus of the present invention, the following effects can be obtained.

  That is, according to the present invention, by changing the resistance value of a variable resistance element such as a PIN diode (p-intrinsic-n Diode) connected as a load to the isolation port of the directional coupler of the detection circuit by a control signal, By adjusting the coupling amount of the directional coupler and changing the distribution ratio of the signal power input to the detector, the detectable range can be expanded.

  Thus, even if only a small number of components such as a variable resistance element, for example, a PIN diode is added, the problems in the conventional technology are solved, and even when the coupling amount of the directional coupler is changed, the main signal line It is possible to realize a detection circuit that is less affected by impedance fluctuations and has a countermeasure that can save space and cost.

It is a circuit diagram which shows an example of the circuit structure of the detection circuit by this invention. It is a circuit diagram for demonstrating operation | movement of the side coupling directional coupler shown in the detection circuit of FIG. FIG. 2 is a characteristic diagram illustrating a relationship between a control current flowing through a PIN diode connected as a load to an isolation port of a side-coupled directional coupler in the detection circuit of FIG. 1 versus a coupling amount. FIG. 2 is a characteristic diagram illustrating a relationship between an output voltage and a detection voltage in each of a control current when a PIN diode is on and a control current when the PIN diode is off in the detection circuit of FIG. 1. It is a circuit diagram which shows the circuit structure of the detection circuit of the conventional microwave radio | wireless communication apparatus. FIG. 6 is a characteristic diagram showing a required detection characteristic of a detector in the conventional detection circuit shown in FIG. 5. It is a characteristic view which shows the ideal detection characteristic of the detector in the conventional detection circuit shown in FIG.

  Preferred embodiments of a detection circuit, a detection method, and a microwave radio communication apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Features of the present invention)
Prior to the description of the embodiments of the present invention, an outline of the features of the present invention will be described first. The present invention relates to a variable resistance element added as a load to an isolation port of a directional coupler, for example, a PIN diode (p-intrinsic-n Diode), in a detection circuit used as a transmission power control circuit of a microwave radio communication device. By changing the resistance value of the directional coupler by the control signal, the coupling amount of the directional coupler is changed, thereby controlling the power supplied to the detector for monitoring the input power and expanding the detectable range. The main feature is to realize a detection circuit, a detection method, and a microwave radio communication apparatus.

  More specifically, the detection circuit of the present invention uses a microstrip line side-coupled directional coupler as a directional coupler, and a variable resistance element such as an isolation port of the side-coupled directional coupler. By using a power distribution circuit in which a PIN diode is added as a load and changing a resistance value of a high-frequency resistor of a variable resistance element, for example, a PIN diode, according to a control signal, the degree of coupling of the side-coupled directional coupler is changed in a plurality of stages. To change the power distribution ratio. As a result, the power distribution ratio can be switched with a small impedance change for the main signal line.

  In addition, since a variable power distributor can be configured by a side coupling directional coupler and a variable resistance element such as a PIN diode, a space-saving and low-cost detection circuit can be realized. As described above, in the present invention, a side-coupled directional coupler for taking out monitor power to the detector by adopting a circuit configuration that has little influence on the impedance fluctuation of the main signal line and has few additional parts. Can be appropriately changed according to the input power level.

(Configuration example of embodiment)
Next, a specific configuration example of the detection circuit according to the present invention will be described in detail with reference to FIG. FIG. 1 is a circuit diagram showing an example of a circuit configuration of a detection circuit according to the present invention. The detection circuit shown in FIG. 1 has a configuration in which a PIN diode is added as a variable resistance element on the load side of the side-coupled directional coupler with respect to the conventional detection circuit shown in FIG. That is, the detection circuit shown in FIG. 1 includes an amplifier 15 that amplifies an input signal, a side-coupled directional coupler 16 that separates a part of the input signal on the main signal line on the monitor line, and a PIN that becomes a variable resistance element. The diode 17 includes at least a detector 18 that evaluates a signal separated on the monitor line and detects an input signal on the main signal line.

  The PIN diode 17 is an example of a variable resistance element, and the high-frequency resistance value can be appropriately changed by a control signal from a control unit that monitors the output of the detector 18. Here, the input-side terminal on the main signal line of the side-coupled directional coupler 16 provided as a directional coupler for separating a part of the input signal on the main signal line is the input port 11 on the main signal line. Are connected to the output port 14, a coupling terminal for drawing a signal to the detector 28 on the monitor line is coupled to the coupling port 12, and a load-side isolation terminal on the monitor line is coupled to the isolation port 13. It is called.

(Description of operation of embodiment)
Next, an example of the operation of the detection circuit in FIG. 1 will be described. First, the operation of the side-coupled directional coupler 16 in which the PIN diode 17 is added as a load on the isolation port 13 side will be described with reference to FIG. FIG. 2 is a circuit diagram for explaining the operation of the side-coupled directional coupler 16 shown in the detection circuit of FIG.

The coupling degree C between the coupling port 12 and the input port 11 of the side coupled directional coupler 16 shown in FIG. 2 is as follows when the electrical length θ of the side coupled directional coupler 16 is π / 4. Is given by equation (1).
C = 20 × log (V2 / V1)
= 20 × log {Z0e ² / (Z2 × Z3 + Z0e ² )
−Z0o ² / (Z2 × Z3 + Z0o ² )} (1)

  Here, Z2 is the load impedance of the coupling port 12, and Z3 is the load impedance of the isolation port 13. Z0e is the even mode impedance of the side coupled directional coupler 16, Z0o is the odd mode impedance of the side coupled directional coupler 16, and both are the shapes of the side coupled directional coupler 16. It is an impedance determined by.

  For example, the degree of coupling C when Z0e = 69.37Ω, Z0o = 36.04Ω, Z2 = 50Ω, and Z3 = 50Ω is −20 [dB].

The input impedance Zin of the input port 11 is given by the following equation (2) when the electrical length θ of the side coupling type directional coupler 16 is π / 4.
Zin = {Z1 × Z4 (Z0o ² + Z0e ² ) + 2 × Z0o ² × Z0e ² }
/ (2 × Z1 × Z4 + Z4 × Z0o ² × Z0e ² ) (2)

  Here, Z1 is the load impedance of the input port 11, and Z4 is the load impedance of the output port 14. As described above, Z0e is the even mode impedance of the side coupled directional coupler 16, Z0o is the odd mode impedance of the side coupled directional coupler 16, and both are side coupled directional characteristics. The impedance is determined by the shape of the coupler 16.

  As can be seen from Equation (2), the input impedance Zin is not affected by the load of the isolation port 13.

Next, the high frequency resistance of the PIN diode 17 will be described. Regarding the voltage-current characteristics of the PIN diode 17, when the current is I and the voltage is V, the relationship of the following expression (3) is established.
I = I0 {exp (qV / kT) -1}
≈I0 {exp (qV / kT)} (3)

  Here, I0 is a reverse saturation current, k is a Boltzmann constant, T is an absolute temperature, and q is an electronic charge amount.

Therefore, the voltage V applied to the PIN diode 17 is approximately:
V = (kT / q) ln (I / I0)
Therefore, the high frequency resistance R of the PIN diode 17 is given by the following equation (4).
R = dV / dI
= (KT / q) × (1 / I) (4)

As shown in FIG. 1, when a PIN diode 17 is added to the isolation port 13 of the side-coupled directional coupler 16, the load impedance Z3 on the side of the isolation port 13 is the high-frequency resistance R of the resistor Z33 and the PIN diode 17. Is given by the following equation (5) using equation (4).
Z3 = Z33 + R
= Z33 + (kT / q) × (1 / I) (5)

  For example, the load impedance Z3 obtained by the equation (5) is substituted into the equation (1), and the side coupling type in the case of Z0e = 69.37Ω, Z0o = 36.04Ω, and Z2 = 50Ω in the above numerical example. By calculating the degree of coupling C between the coupling port 12 and the input port 11 of the directional coupler 16, the relationship between the control current I flowing through the PIN diode 17 and the coupling amount C can be obtained. The calculation result based on the calculation formula of Formula (5) is shown in FIG. FIG. 3 is a characteristic diagram showing the relationship between the control current I and the coupling amount C flowing in the PIN diode 17 connected as a load to the isolation port 13 of the side coupled directional coupler 16 in the detection circuit of FIG.

As shown in the characteristic diagram of FIG. 3, a control current Ion that flows when the PIN diode 17 is on and a control current Ioff that flows when the PIN diode 17 is off, respectively,
Ion = 3.5mA
Ioff = 25 μA
The coupling amounts Con and Coff are as follows.
Con = −10 dB
Coff = -25 dB
It turns out that it is.

  Next, FIG. 4 shows the relationship between the output power Pout of the detection target signal and the detection voltage Vdet at Ion and Ioff. FIG. 4 is a characteristic diagram showing the relationship between the output power Pout and the detection voltage Vdet in the control current Ion when the PIN diode 17 is on and the control current Ioff when the PIN diode 17 is off in the detection circuit of FIG.

  In the case of the conventional detection circuit shown in FIG. 5, the detectable range of the detector 28 is +30 dBm to −5 dBm, as shown in FIG. However, in the detection circuit of the present embodiment shown in FIG. 1, the control current flowing through the PIN diode 17 is changed by the control signal, so that the detectable range of the detector 28 can be further expanded. That is, as shown in FIG. 3, when the signal power level from the amplifier 15 is a high output higher than a predetermined high power threshold, the control current of the PIN diode 17 is set to a control current Ioff at the time of OFF of 25 μA. To do. On the other hand, when the signal power level from the amplifier 15 is a low output lower than a predetermined low power threshold, the control current Ion when the PIN diode 17 is on is set to 3.5 mA.

  In other words, as described above, the PIN diode 17 is a variable resistance element capable of changing the resistance value of the high-frequency resistor by the control signal, and the signal power level from the amplifier 15 is higher than the high power threshold value. Increases the resistance value of the PIN diode 17 by reducing the control current flowing through the PIN diode 17 as a control signal to Ioff = 25 μA, while the signal power level from the amplifier 15 is lower than the low power threshold. In this case, the resistance value of the PIN diode 17 is set low by increasing the control current passed through the PIN diode 17 to Ion = 3.5 mA.

  As a result, as shown in FIG. 4, the detectable range can be greatly expanded from +30 dBm to −20 dBm compared to the conventional detection circuit.

  Further, as shown in the equation (2), in the detection circuit of the present embodiment shown in FIG. 1, the fluctuation of the load on the isolation port 13 side does not affect the input impedance Zin in the main signal line. Therefore, the power distribution ratio of the side-coupled directional coupler 16 can be switched under an environment where the impedance change is small for the main signal.

  In the detection circuit shown in FIG. 1, the case where the PIN diode 17 is used as the variable resistance element connected to the isolation port 13 of the side-coupled directional coupler 16 is exemplified. It is not limited to. For example, an FET (Field Effect Transistor) or a bipolar transistor may be used, or a variable resistor may be used, and the resistance value can be variably controlled by a control signal. Any type of element may be used as long as it is.

  The detection circuit having the above configuration can be suitably applied as a detection circuit in a microwave radio communication apparatus that transmits and receives a radio signal in the microwave band.

(Explanation of effect of embodiment)
As described in detail above, the following effects are obtained in the present embodiment.

  That is, according to the present embodiment, the load of the variable resistance element added to the isolation port 13 of the side-coupled directional coupler 16 of the detection circuit, for example, the PIN diode 17 is changed by the control signal, thereby changing the side-coupled direction. By adjusting the coupling amount of the sexual coupler 16 and changing the distribution ratio of the signal power input to the detector 18, the detectable range can be expanded.

  Thus, even if only a small number of components such as a variable resistance element, for example, a PIN diode 17 is added, the problems of the prior art are solved and the coupling amount of the side coupling type directional coupler 16 is changed. Thus, it is possible to realize a detection circuit that is less affected by impedance fluctuations in the main signal line, and that is provided with measures that can save space and cost.

  The configuration of the preferred embodiment of the present invention has been described above. However, it should be noted that such embodiments are merely examples of the present invention and do not limit the present invention in any way. Those skilled in the art will readily understand that various modifications and changes can be made according to a specific application without departing from the gist of the present invention.

11 Input Port 12 Coupling Port 13 Isolation Port 14 Output Port 15 Amplifier 16 Side Coupling Directional Coupler 17 PIN Diode 18 Detector 21 Input Port 22 Coupling Port 23 Isolation Port 24 Output Port 25 Amplifier 26 Side Coupling Direction Sexual coupler 28 Detector

Claims (6)

  A directional coupler inserted to separate a part of the main signal on a main line propagating a main signal in the microwave band, and a detector for detecting a signal partially separated by the directional coupler. A detection circuit for detecting the main signal, wherein a variable resistance element capable of changing a resistance value by a control signal is connected to the isolation port side of the directional coupler as a load. A detection circuit characterized by that.   When the power level of the main signal input to the directional coupler is higher than a predetermined high power threshold, the resistance value of the variable resistance element is increased, while the power level of the main signal is set in advance. 2. The detection circuit according to claim 1, wherein when the threshold value is lower than a predetermined low power threshold value, the resistance value of the variable resistance element is lowered.   3. The variable resistance element is a PIN diode (p-intrinsic-n Diode), a FET (Field Effect Transistor), a bipolar transistor, or a variable resistor. The detection circuit described in 1.   A directional coupler inserted to separate a part of the main signal on a main line propagating a main signal in a microwave band; a detector for detecting a signal partially separated by the directional coupler; A detection method for detecting the main signal, comprising at least a variable resistive element connected as a load to the isolation port side of the directional coupler and capable of changing a resistance value by a control signal, When the power level of the main signal input to the directional coupler is higher than a predetermined high power threshold value, the resistance value of the variable resistance element is increased, while the power level of the main signal is determined in advance. And a resistance value of the variable resistance element is lowered when the threshold value is lower than the low power threshold.   5. The variable resistance element according to claim 4, wherein any one of a PIN diode (p-intrinsic-n Diode), a FET (Field Effect Transistor), a bipolar transistor, or a variable resistor is used as the variable resistance element. Detection method.   A microwave radio communication apparatus for transmitting and receiving a radio signal in a microwave band, wherein the detection circuit according to any one of claims 1 to 3 is used as a detection circuit for detecting a signal.

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