JP4661723B2 - Control device for variable attenuator - Google Patents

Description

  The present invention relates to a control device for a variable attenuator capable of continuously varying an attenuation amount of a high-frequency signal (RF signal).

  A variable attenuator (attenuator) is used to adjust the power of a high-frequency signal in mobile communication devices such as mobile phones and other electronic devices using high-frequency signals. In recent years, a variable attenuator using a PIN diode capable of continuously varying the attenuation amount of a high-frequency signal has been frequently used. FIG. 6 is a circuit diagram showing an example of a conventional variable attenuator. There are various types of variable attenuators such as T-type, O-type, and π-type. FIG. 6 shows a π-type variable attenuator as an example.

  A conventional variable attenuator 100 shown in FIG. 6 has a pair of left and right PIN diodes 102 and 103 in series in the middle of a signal line 101 connecting an input terminal T11 and an output terminal T12 to which a high frequency signal such as a microwave is input. In addition, the cathodes of a pair of left and right PIN diodes 104 and 105 are connected in a shunt form to the cathode side of the pair of PIN diodes 102 and 103. The anode sides of the PIN diodes 104 and 105 are grounded via bypass capacitors 106 and 107, respectively.

Further, choke coils 108 and 109 for blocking high frequency components are connected to the anode side of the PIN diodes 104 and 105. The connection points of the choke coils 108 and 109 are connected to a connection terminal 110 to which a bias current (hereinafter referred to as a parallel control current) I12 applied to the PIN diodes 104 and 105 is supplied. On the other hand, one end of a high-frequency component blocking choke coil 111 is connected to the anode side of the PIN diodes 102 and 103, and the other end of the choke coil 111 is connected to a bias current (hereinafter referred to as the PIN diodes 102 and 103). It is connected to a connection terminal 112 to which I11 (referred to as series control current) is supplied.

Note that the capacitors 113 and 115 in FIG. 6 remove the DC component of the high-frequency signal (low impedance with respect to the high-frequency component), and the coils 114 and 116 are RF choke coils. Here, the variable attenuator is generally designed to match the characteristic impedance. The matching conditions of the π-type variable attenuator shown in FIG. 6 are expressed by the following equations (1) and (2).
R ₁₁ = Z / 2 ((k ² −1) / k) (1)
R ₁₂ = Z ((k + 1) / (k-1) (2)

Here, R _{11 on} the left side of the equation (1) is a combined resistance of the PIN diodes 102 and 103, and R _{12 on} the left side of the equation (2) is a resistance of each of the PIN diodes 104 and 105. However, Z in the above equations (1) and (2) is the input / output characteristic impedance [Ω] of the variable attenuator 100, and k is k = log ⁻¹ (n / 20).

  In the variable attenuator 100 having the above configuration, the resistance (high-frequency resistance component) of the PIN diodes 104 and 105 changes when the parallel control current I12 is varied, and the resistance (high-frequency resistance) of the PIN diodes 102 and 103 changes when the series control current I11 is varied. Resistance component) changes. Therefore, by controlling the parallel control current I12 and the series control current I11, respectively, the attenuation amount of the variable attenuator 100 can be continuously varied while satisfying the matching conditions expressed by the above equations (1) and (2). It becomes possible.

  FIG. 7 is a block diagram showing a first conventional example of a control device that controls the attenuation amount of the variable attenuator 100. As described above, the variable attenuator 100 shown in FIG. 6 needs to control the parallel control current I12 and the series control current I11. Therefore, the control device 200 shown in FIG. 7 includes a control signal generator 201 and a parallel control current generation circuit 203 for controlling the parallel control current I12, a control signal generator 202 for controlling the series control current I11, and And a series control current generation circuit 204.

  The control signal generator 201 outputs a control signal that defines the amount of parallel control current I12, and the parallel control current generation circuit 203 generates a parallel control current I12 corresponding to the control signal output from the control signal generator 201. . Similarly, the control signal generator 202 outputs a control signal that defines the amount of the series control current I11, and the series control current generation circuit 204 outputs a series control current I11 according to the control signal output from the control signal generator 202. Is generated.

  FIG. 8 is a block diagram showing a second conventional example of a control device that controls the attenuation amount of the variable attenuator 100. 7 includes a control signal generator 301 and a parallel control current generation circuit 302 for controlling the parallel control current I12, a detector 303, a comparator 304, a control signal generator 305, and a series control current generator. A circuit 306 is provided. The control signal generator 301 outputs a control signal that defines the amount of parallel control current I12, and the parallel control current generation circuit 302 generates a parallel control current I12 corresponding to the control signal output from the control signal generator 301. .

  The detector 303 detects the high frequency signal output from the variable attenuator 100. The comparator 304 compares the detection signal of the detector 303 with the control signal output from the control signal generator 305, and outputs a comparison signal indicating the comparison result. The series control current generation circuit 306 generates a series control current I11 corresponding to the comparison signal output from the comparator 304. That is, in the control device 300 shown in FIG. 8, the detection signal of the detector 303 is output from the control signal generator 305 by the detector 303, the comparator 304, the control signal generator 305, and the series control current generation circuit 306. While automatic level control (ALC: Auto Level Control) of the series control current I11 is performed to match the signal, the parallel control current I12 needs to be separately controlled.

The details of the conventional variable attenuator 100 shown in FIG. 6 are, for example, the following Patent Document 1, and the details of the conventional variable attenuator control devices 200, 300 shown in FIGS. See US Pat.
JP 2000-286659 A JP 2004-228710 A

  Incidentally, in the control device 200 of the first conventional example shown in FIG. 7, since it is necessary to control the two control signal generators 201 and 202 separately, the control data and control signal generation for the control signal generator 201 are required. Two types of control data are required, including control data for the device 202. Therefore, for example, in the case where individual variation of the variable attenuator 100 is calibrated, the amount of control data increases dramatically, and a large amount of memory capacity is required to store the control data. There is a problem that time becomes long.

  Further, in the control device 300 of the second conventional example shown in FIG. 8, the automatic control is performed for the series control current I11, but the parallel control current I12 is controlled without feedback without performing the automatic level control. Is going. Here, the amount of current of the parallel control current I12 is controlled by a control signal from the control signal generator 301. However, if the series control current I11 fluctuates due to temperature fluctuation or the like, the optimum impedance There is a problem that consistency cannot be obtained. Since the control device 300 also includes two control signal generators 301 and 305, two types of control data are required, and there is a problem similar to that of the first conventional example.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a control device for a variable attenuator that can easily realize an optimum impedance matching of the variable attenuator with one control signal.

In order to solve the above problem, the control device for a variable attenuator according to the present invention substantially reverses the second control current (I2) from the outside with respect to the current obtained by logarithmically converting the first control current (I1) from the outside. In the variable attenuator control device (10, 40) for controlling the variable attenuator (20) having a circuit characteristic capable of continuously varying the attenuation while satisfying the impedance matching condition by making the ratio proportional , A control signal generator (11-13) for generating a control signal (C1) for controlling the attenuation amount of the variable attenuator, and the first control current corresponding to the control signal generated by the control signal generator. a first control current generating circuit for generating (14), to said control signal from said control signal generating unit, in accordance with the circuit characteristic of said variable attenuator such that the matching conditions of the impedance in said variable attenuator is satisfied Conversion unit that performs several converted (15, 41), and further comprising a second control current generating circuit (16) for generating said second control current corresponding to the converted control signal at the converting unit .
According to this invention, the control signal from the control signal generator is input to the first control current generator and the converter. A first control current is generated when a control signal is input to the first control current generation circuit. On the other hand, when the control signal is input to the converter , logarithmic conversion corresponding to the circuit characteristics of the variable attenuator is performed so that the impedance matching condition in the variable attenuator is satisfied. Then, the converted control signal is input to the second control current generation circuit to generate a second control current.
In the control device for a variable attenuator according to the present invention, the control unit converts the logarithmically converted control signal so that the relationship between the logarithmically converted first control current and the second control current is a broken line. A broken line circuit (41) to be operated is provided.
In the variable attenuator control device according to the present invention, the variable attenuator is connected in series between the input and output terminals, and the first diode (22 to 25) whose bias current is controlled by the first control current. And a second diode (26, 27) connected in parallel between the input / output terminals and having a bias current controlled by the second control current.

  According to the present invention, the first control current is generated based on the control signal from the control signal generator, and the impedance matching condition in the variable attenuator is satisfied with respect to the control signal from the control signal generator. Since the second control current is generated by performing a predetermined conversion according to the circuit characteristics of the variable attenuator, it is possible to easily realize the optimum impedance matching of the variable attenuator with one control signal. is there.

  Hereinafter, a control device for a variable attenuator according to an embodiment of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram illustrating a control device for a variable attenuator according to a first embodiment of the present invention. The control device 10 shown in FIG. 1 is a control device that controls the attenuation amount while satisfying the impedance matching condition of the variable attenuator 20, and includes a detector 11, a comparator 12, a reference control signal generator 13, and serial control. A current generation circuit 14, a converter 15, and a parallel control current generation circuit 16 are provided.

  The variable attenuator 20 to be controlled is capable of continuously varying the attenuation while satisfying the impedance matching condition by two input control currents (series control current I1 and parallel control current I2). FIG. 2 is a circuit diagram illustrating an example of the variable attenuator 20. There are various types of variable attenuators such as T-type, O-type, and π-type. FIG. 2 shows a π-type variable attenuator as an example.

  The variable attenuator 20 shown in FIG. 2 includes two pairs of PIN diodes 22 and 23 and a PIN diode in the middle of a signal line 21 connecting an input terminal T1 and an output terminal T2 to which a high frequency signal such as a microwave is input. 24 and 25 are inserted in series, and the cathodes of a pair of left and right PIN diodes 26 and 27 are connected in a shunt shape to the cathode side of the PIN diodes 22 and 23, respectively. The anode sides of the PIN diodes 26 and 27 are grounded via bypass capacitors 28 and 29, respectively.

  Further, one ends of damping resistors 30 and 31 are connected to the anode side of the PIN diodes 26 and 27, and a choke coil 32 for cutting off high frequency components is connected to the other ends of these damping resistors 30 and 31. . The other end of the choke coil 32 is connected to a connection terminal 33 to which a bias current (parallel control current: second control current) I2 applied to the PIN diodes 26 and 27 is supplied. On the other hand, one end of a high-frequency component blocking choke coil 34 is connected to the anode side of the PIN diodes 24 and 25, and the other end of the choke coil 34 has a bias current (series control) applied to the PIN diodes 22 to 25. (Current: first control current) I1 is connected to a connection terminal 35 to which the current is supplied. The capacitors 36 and 38 in FIG. 2 remove the DC component of the high-frequency signal (low impedance with respect to the high-frequency component), and the coils 37 and 39 are RF choke coils.

  In the variable attenuator 20 having the above configuration, when the parallel control current I2 is varied, the resistances (high frequency resistance components) of the PIN diodes 26 and 27 change, and when the series control current I1 is varied, the resistances (high frequency) of the PIN diodes 22-25. Resistance component) changes. Therefore, if the series control current I1 and the parallel control current I2 are respectively controlled, it is possible to continuously vary the attenuation amount of the variable attenuator 20 while satisfying the impedance matching condition.

  Returning to FIG. 1, the detector 11 detects a high-frequency signal output from the output terminal T <b> 2 of the variable attenuator 20. The comparator 12 compares the detection signal of the detector 11 with the reference control signal output from the reference control signal generator 13, and outputs a control signal C1 indicating the comparison result. The reference control signal output from the reference control signal generator 13 is a reference signal for controlling the attenuation amount of the variable attenuator 20, and the control signal C1 is used to actually control the attenuation amount of the variable attenuator. Signal. The series control current generation circuit 14 generates a series control current I1 corresponding to the control signal C1 output from the comparator 12.

  The converter 15 performs predetermined conversion on the control signal C1 output from the comparator 12 according to the circuit characteristics of the variable attenuator 20 so that the impedance matching condition in the variable attenuator 20 is satisfied. Specifically, the converter 15 performs logarithmic conversion on the control signal C <b> 1 according to the circuit characteristics of the variable attenuator 20. The parallel control current generation circuit 16 generates a parallel control current I2 corresponding to the control signal converted by the converter 15.

  As described above, the control device 10 for the variable attenuator according to the present embodiment includes the control signal generation unit including the detector 11, the comparator 12, and the reference control signal generator 13, the series control current generation circuit 14, and the converter 15. And the parallel control current generator circuit 16 automatically controls the level of the series control current I1 and the parallel control current I2 (ALC: ALC) so that the detection signal of the detector 11 matches the reference control signal output from the reference control signal generator 13. Auto Level Control) is performed.

  Here, the circuit characteristics of the variable attenuator 20 will be described. FIG. 3 is a diagram illustrating circuit characteristics of the variable attenuator 20. The graph shown in FIG. 3 is a graph showing the relationship between the series control current I1, the attenuation of the variable attenuator 20, and the parallel control current I2 when the impedance matching condition is satisfied for a high frequency signal having a frequency of 4 GHz. It is. In the graph shown in FIG. 3, the horizontal axis represents the series control current I1, the left vertical axis represents the attenuation of the variable attenuator 20, and the right vertical axis represents the parallel control current I2. . The horizontal axis indicating the series control current I1 is logarithmically displayed.

  In FIG. 3, the curve denoted by reference symbol L1 is a graph showing the relationship between the series control current I1 and the attenuation of the variable attenuator 20 when the optimum impedance matching condition is satisfied, and the curve denoted by reference symbol L2 These are graphs showing the relationship between the series control current I1 and the parallel control current I2 when the optimum impedance matching condition is satisfied. Referring to the curve L1 in FIG. 3, when the series control current I1 increases continuously, the attenuation amount of the variable attenuator 20 also increases continuously. Conversely, when the series control current I1 decreases continuously, the variable attenuator 20 It can be seen that the amount of attenuation decreases continuously.

  On the other hand, referring to the curve L2, when the series control current I1 increases continuously, the parallel control current I2 decreases continuously. Conversely, when the series control current I1 decreases continuously, the parallel control current I2 increases continuously. I understand that Moreover, the relationship between the logarithmically displayed series control current I1 and parallel control current I2 is substantially linear. If each of the series control current I1 and the parallel control current I2 is controlled so as to have the relationship indicated by the curve L2, the optimum impedance matching condition is satisfied.

  However, in order to realize the relationship indicated by the curve L2, the circuit scale increases and the control becomes complicated. Therefore, in the present embodiment, by controlling the relationship between the series control current I1 and the parallel control current I2 to be an approximate straight line L3 obtained by linearly approximating the curve L2, the impedance matching condition that does not cause a practical problem is satisfied. I am doing so. In the present embodiment, a converter 15 that performs logarithmic conversion on the control signal C1 is provided in the preceding stage of the parallel control current generation circuit 16 so that the relationship between the series control current I1 and the parallel control current I2 is an approximate straight line L3. is doing. As described above, in the present embodiment, almost optimum impedance matching can be easily realized with a simple configuration in which the converter 15 is simply provided in front of the parallel control current generation circuit 16.

  Further, in this embodiment, since the attenuation amount of the variable attenuator 20 can be controlled by only one reference signal generator 13, a large memory capacity is required to store control data as in the conventional case. There is no problem that the time required for calibration becomes longer. Further, since both the control currents of the series control current I1 and the parallel control current I2 are feedback-controlled, even if the temperature or the like fluctuates, it can be set to an arbitrary attenuation amount while maintaining almost optimum impedance matching. Furthermore, since a circuit for performing general logarithmic conversion can be used as the converter 15 and the circuit scale does not increase so much, the circuit scale can be increased as compared with the case where the series control current I1 and the parallel control current I2 are individually controlled. It can be simplified.

[Second Embodiment]
FIG. 4 is a block diagram showing a control device for a variable attenuator according to a second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the structure same as the control apparatus 10 of the variable attenuator by 1st Embodiment shown in FIG. The variable attenuator control device 40 shown in FIG. 4 is different from the variable attenuator control device 10 shown in FIG. 1 in that a broken line circuit 41 is provided between the converter 15 and the parallel control current generation circuit 16. is there.

  The broken line circuit 41 is a circuit that operates the control signal converted by the converter 15 so that the relationship between the logarithmically converted series control current I1 and the parallel control current I2 becomes a broken line. FIG. 5 is a diagram for explaining an operation performed in the broken line circuit 41. In FIG. 5, a graph similar to that in FIG. 3 is shown. That is, a curve L1 indicating the relationship between the series control current I1 and the attenuation amount of the variable attenuator 20 and a curve L2 indicating the relationship between the series control current I1 and the parallel control current I2 are illustrated.

  As described with reference to FIG. 3, in the control device 10 of the first embodiment, the converter 15 is provided and the series control current I1 and the parallel control current I2 logarithmically converted are linearly approximated. However, as can be seen from FIG. 3, the relationship between the approximate straight line L3, the actual series control current I1, and the parallel control current I2 is caused by the current-resistance characteristics of the PIN diodes 22 to 27, the circuit parasitic element characteristics at high frequencies, and the like. As a result, deviation occurs. The control device 40 of the present embodiment attempts to match the actual circuit characteristics by making the relationship between the logarithmically converted series control current I1 and parallel control current I2 a broken line.

  In the example shown in FIG. 5, the series control current I1 and the parallel control current I2 logarithmically converted by the broken line circuit 41 are approximated by a broken line L4 composed of three straight line portions. In the broken line L4, a portion indicated by a reference symbol P1 and a portion indicated by a reference symbol P2 in FIG. Comparing FIG. 5 and FIG. 3, it can be seen that the approximation by the broken line L4 shown in FIG. 5 is closer to the actual circuit characteristics (the relationship between the logarithmically converted series control current I1 and the parallel control current I2).

  As described above, in the present embodiment, since the relationship between the series control current I1 and the parallel control current I2 is controlled to be the broken line L4, it is possible to perform impedance matching more optimal than the first embodiment. . In addition, in the example shown in FIG. 5, although it approximated by the broken line which consists of three linear parts which have two broken points P1, P2, the number of broken points is arbitrary.

Although the variable attenuator control device according to the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and can be freely changed within the scope of the present invention. For example, in the above embodiment, the case where feedback control is performed on both the control currents of the series control current I1 and the parallel control current I2 has been described as an example. However, the present invention can also be applied to a case where feedback control is not performed. . That is, according to the present invention, the detector 11 and the comparator 12 shown in FIGS. 1 and 4 are not necessarily indispensable configurations. However, in order to maintain stability against temperature changes and the like, it is desirable to provide feedback control with these.

It is a block diagram which shows the control apparatus of the variable attenuator by 1st Embodiment of this invention. 3 is a circuit diagram illustrating an example of a variable attenuator 20. FIG. 3 is a diagram illustrating circuit characteristics of the variable attenuator 20. FIG. It is a block diagram which shows the control apparatus of the variable attenuator by 2nd Embodiment of this invention. 5 is a diagram for explaining an operation performed in a broken line circuit 41. FIG. It is a circuit diagram which shows an example of the conventional variable attenuator. It is a block diagram which shows the 1st prior art example of the control apparatus which controls the attenuation amount of the variable attenuator 100. It is a block diagram which shows the 2nd prior art example of the control apparatus which controls the attenuation amount of the variable attenuator 100.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Control device of variable attenuator 11 Detector 12 Comparator 13 Reference control signal generator 14 Series control current generation circuit 15 Converter 16 Parallel control current generation circuit 20 Variable attenuator 22-25 PIN diode 26, 27 PIN diode 40 Variable Attenuator control device 41 Polygonal line circuit C1 Control signal I1 Series control current I2 Parallel control current

Claims (3)

A circuit capable of continuously varying the attenuation while satisfying the impedance matching condition by making the second control current from the outside substantially inversely proportional to the logarithmically converted current of the first control current from the outside. In a control device for a variable attenuator for controlling a variable attenuator having characteristics ,
A control signal generator for generating a control signal for controlling the attenuation of the variable attenuator;
A first control current generating circuit for generating the first control current according to the control signal generated by the control signal generator;
A conversion unit that performs logarithmic conversion in accordance with circuit characteristics of the variable attenuator so that an impedance matching condition in the variable attenuator is satisfied with respect to the control signal from the control signal generation unit;
A control device for a variable attenuator, comprising: a second control current generation circuit that generates the second control current according to the control signal converted by the conversion unit. The said conversion part is provided with the broken line circuit which operates the said control signal which performed logarithmic conversion so that the relationship between the said 1st control current logarithmically converted and the said 2nd control current may become a broken line. The control device of the variable attenuator according to 1. The variable attenuator is connected in series between input and output terminals, and a first diode whose bias current is controlled by the first control current;
  A second diode connected in parallel between the input and output terminals and having a bias current controlled by the second control current;
  The control device for a variable attenuator according to claim 1 or 2, further comprising:

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