JP4385227B2 - Phase shifter and control method thereof - Google Patents

Description

  The present invention relates to a phase shifter and a control method thereof, and more particularly to a reflective phase shifter.

  A phase shifter is a device that can arbitrarily control the phase of various signals by changing the applied DC voltage. In the field of wireless communication equipment and other electronic equipment, phase shifters are very useful and are used for various applications such as linearizers. As performance required for the phase shifter, first, a large phase variable range is the first, but in addition, there is a small passage loss fluctuation at the time of phase change. This is because if the variation in the passage loss of the phase shifter is large at the time of phase change, it is necessary to perform adjustment using a variable attenuator to correct this.

  As an example of the circuit configuration of the phase shifter, there has conventionally been one using a varactor diode. Either the anode electrode or the cathode electrode of the varactor diode is grounded, and a reverse bias voltage is applied to the other electrode. By changing the reverse bias voltage, the capacitance between the terminals of the varactor diode is changed. The phase change of the signal is realized by changing the reflection impedance of the varactor diode by changing the capacitance between the terminals.

  Here, the reflection coefficient of the varactor diode changes as the inter-terminal capacitance changes. This is due to the equivalent series resistance Rs of the varactor diode. The above-described change in the reflection coefficient of the varactor diode due to the change in capacitance is directly linked to the fluctuation of the passage loss of the phase shifter.

  As an example of a technique for solving the above-described passage loss fluctuation, there is an example disclosed in Patent Document 1. By connecting a resistor in parallel with the varactor diode, the change in the reflection coefficient of the varactor diode due to the change in the capacitance between the terminals is kept almost constant, and as a result, the fluctuation in the passage loss of the phase shifter during the phase change is suppressed. It is. However, the equivalent series resistance Rs of an actual varactor diode changes with a change in capacitance between terminals. Due to the change in equivalent series resistance Rs accompanying this change in capacitance between terminals, the effect of maintaining the reflection coefficient of the varactor diode constant due to the change in capacitance between terminals by connecting the resistor in parallel with the varactor diode is reduced. Therefore, the effect of suppressing the passage loss fluctuation of the phase shifter at the time of phase change is also reduced.

  Therefore, in order to further suppress the passage loss fluctuation of the phase shifter at the time of the phase change, a technique is required to suppress the passage loss fluctuation by suppressing the equivalent series resistance change of the varactor diode.

  FIG. 6 shows an example of a circuit configuration of a conventional reflective phase shifter. Referring to FIG. 6, the conventional reflection type phase shifter of this type applies a DC voltage for changing the inter-terminal capacitance of the high-frequency signal input terminal 1, the high-frequency signal output terminal 2, and the variable capacitance elements 7a and 7b. The DC voltage application terminal 3, the DC voltage blocking capacitors 4a and 4b, the RF choke coils 5a and 5b, and the high frequency signal shifted in phase due to the capacitance change between the terminals of the variable capacitance element are combined in phase, and the high frequency signal input terminal 1 and the high frequency signal are combined. It is composed of a 90 degree 3 dB hybrid 6 for isolating between the signal output terminal 2 and varactor diodes 7a and 7b as variable capacitance elements.

  For the sake of explanation, a part of FIG. 6 is extracted (only one of them is symmetrical in FIG. 6), and the circuit configuration is shown in FIG. 7. In FIG. Show by number. Further, in the circuit configuration of FIG. 7, when the reverse bias voltage applied to the varactor diode 7 is changed, that is, the voltage applied to the DC voltage application terminal 3 is changed, and the capacitance between the terminals of the varactor diode 7 is changed. FIG. 8 shows the locus of the reflection coefficient at the high-frequency signal input terminal 1 on the Smith chart.

  Referring to FIG. 8, the reflection coefficient | ΓA | at the terminal-to-terminal capacitance minimum point A of the varactor diode 7 is different from the reflection coefficient | ΓB | at the terminal-to-terminal capacitance maximum point B, that is, point A and point B. Therefore, the return loss is different. This is due to the DC resistance Rs of the varactor diode 7. Thus, since the return loss changes when the capacitance between the terminals of the varactor diode 7 changes, the reflection type phase shifter having the configuration shown in FIG. 6 changes the reverse bias voltage applied to the varactor diodes 7a and 7b, When the capacitance between the terminals of the varactor diode is changed, the passage loss of the phase shifter itself will fluctuate.

As an example of a technique for solving this, there is an example disclosed in Patent Document 1 described above. This circuit configuration is shown in FIG. In this configuration, capacitors 8a and 8b and resistors 9a and 9b are added to the reflection type phase shifter shown in FIG. The resistance values Ra of the resistors 9a and 9b are values derived from the equation (1) when the characteristic impedance of the phase shifter body is Z0 and the equivalent series resistance of the varactor diodes 7a and 7b is Rs.
Ra = Z0 [1 + √ {1 + 4 (Rs / Z0) ² }] / (2Rs / Z0)
...... (1)

  Due to the resistors 9a and 9b, the locus of the reflection coefficient on the Smith chart moves substantially concentrically with respect to the center, that is, the reflection coefficient becomes a substantially constant value with respect to the capacitance change of the varactor diodes 7a and 7b. As a result, the passage loss fluctuation of the phase shifter can be suppressed.

Japanese Patent Laid-Open No. 04-047801 JP 11-12205 A

  However, Rs of an actual varactor diode is not constant with respect to a change in inter-terminal capacitance, and has characteristics as shown in FIG. . FIG. 10 shows an example of a change in Rs with respect to a change in inter-terminal capacitance read from a catalog of products sold by a company as an example of a general varactor diode. FIG. 11 shows the result of simulating the reflection coefficient of a single varactor diode in consideration of the change in Rs with respect to the change in capacitance between terminals of the varactor diode. The characteristics of the resistance value Ra derived from the equation (1) with and without the resistance Rs are compared.

  FIG. 11A shows the characteristic of the reflection coefficient, and FIG. 11B shows the characteristic of the reflection loss with respect to the inter-terminal capacitance. As can be seen from FIG. 11, the characteristics with the resistance are smaller in the variation of the reflection coefficient and the variation in the reflection loss with respect to the change in the capacitance between the terminals of the varactor diode as compared with the case without the resistance. I understand.

  However, even when the resistance is present when the inter-terminal capacitance is changed in the range of 0.5 to 7.2 pF, in this example, the reflection loss fluctuation of about 0.4 dBp-p still remains. Therefore, in order to further reduce the passage loss fluctuation due to the change in the capacitance between the terminals of the varactor diode, it is necessary to reduce the fluctuation of Rs of the varactor diode when the capacitance between the terminals is changed as much as possible.

  Patent Document 2 discloses a high-frequency phase shifter with a high-frequency switch in which a PIN diode is connected in series with a varactor diode. The PIN diode in this case is for operating as a switching function. For this reason, the method of supplying a DC bias to the PIN diode is for turning on and off the PIN diode.

  An object of the present invention is to provide a reflection type phase shifter capable of suppressing a change in equivalent series resistance of a varactor diode due to a change in capacitance between terminals and suppressing a variation in a passage loss at the time of a transfer change, and a control method thereof. It is to be.

  A phase shifter according to the present invention includes a varactor diode as a variable capacitance element and a hybrid for synthesizing a signal phase-shifted by a change in capacitance of the varactor diode and isolating between signal input / output terminals. The phase shifter includes a PIN diode that is connected in series to the varactor diode and cancels a change in resistance caused when the capacitance of the varactor diode changes.

  In addition, the method for controlling a phase shifter according to the present invention combines the varactor diode as a variable capacitance element and the signal phase-shifted due to the change in capacitance of the varactor diode, and isolates the signal input / output terminals. A phase shifter control method for changing the capacitance of the varactor diode, and a PIN diode that is connected in series to the varactor diode and cancels a resistance change caused when the capacitance of the varactor diode changes. And a step of generating a forward bias voltage that changes with respect to the PIN diode in accordance with a change in the reverse bias voltage applied to the varactor diode.

  The operation of the present invention will be described. A hybrid for isolating high-frequency signal input / output terminals, a varactor diode as a variable capacitance element, a DC voltage application terminal for applying a DC voltage to change the capacitance between terminals of the varactor diode, and a varactor diode A high-frequency signal shifted in phase due to a change in capacitance between terminals, and a resistor for suppressing a change in the return loss of the varactor diode due to a change in capacitance between the terminals of the varactor diode at the high-frequency signal input / output terminal, In a reflection type phase shifter having a capacitor for preventing a DC voltage from being applied to a resistor, a PIN diode is connected in series with a varactor diode, and an equivalent series of varactor diodes accompanying a change in capacitance between terminals of the varactor diode Suppresses changes in resistance and suppresses the passage loss fluctuation of the phase shifter.

  According to the present invention, it is possible to suppress the variation of the equivalent series resistance of the varactor diode due to the change in the capacitance between the terminals, and to suppress the fluctuation of the passage loss of the reflection type phase shifter at the time of the phase shift change. is there.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram of an embodiment of the present invention, and the same parts as those in FIGS. PIN diodes 10a and 10b are connected in series with varactor diodes 9a and 9b, respectively, in order to suppress the change in Rs of the varactor diode when the inter-terminal capacitance is changed as described above. Generally, a PIN diode is a variable resistance element that can be regarded as a pure resistance equivalently when a forward bias voltage is applied, and whose resistance value can be changed by changing a forward bias current. is there.

  As the forward bias current is increased, the equivalent series resistance value decreases exponentially. By utilizing the characteristic of the PIN diode that the resistance value can be changed by this forward bias current change, the change in Rs of the varactor diode when the capacitance between terminals is changed is suppressed. FIG. 3 is a diagram for explaining the means for suppressing the change in Rs of the varactor diode when the capacitance between the terminals is changed using the characteristics of the PIN diode. The characteristics plotted with diamonds in FIG. 3 are obtained by re-plotting the state of Rs change of the product shown in FIG. 10 as the absolute value of the reverse bias voltage of the varactor diode applied to the DC voltage terminal 3 on the horizontal axis. Is.

  On the other hand, the characteristic plotted with a triangle mark in the graph is a plot of the change in resistance value desired for the PIN diode when the horizontal axis is the absolute value of the bias voltage applied to the DC voltage terminal 3. is there. The characteristic plotted with cross marks in the graph is a plot of the combined resistance value when a varactor diode having the characteristics plotted with diamonds and a PIN diode with the characteristics plotted with triangles are connected in series. It is. As shown in the graph, the combined resistance value characteristic is maintained at a constant value (2Ω in this example) with respect to the bias voltage applied to the DC voltage terminal 3.

  FIG. 2 shows a circuit configuration diagram in which a part of the circuit configuration of the reflection type phase shifter proposed this time shown in FIG. 1 is extracted (only one of them is symmetrical in FIG. 1). Equivalent parts are indicated by the same numbers. A PIN diode 10 and a varactor diode 7 are connected in series. A DC voltage applied to the DC voltage application terminal 3 is applied to the anode electrode of the PIN diode 10 through the DC network 15 and the RF choke coil 12. In addition, a constant DC voltage applied to the reference voltage application terminal 14 is applied to the cathode electrode of the PIN diode 10 through the RF choke coil 13.

  As shown in FIG. 3, in order to suppress the Rs change of the varactor diode 7 when the inter-terminal capacitance changes, the resistance value increases as the absolute value of the voltage applied to the DC voltage application terminal 3 increases. Characteristics are required for the PIN diode 10. However, the PIN diode 10 alone has a characteristic that the resistance value decreases as the forward bias voltage increases. In order to correct the contradictory characteristics, a constant DC voltage is applied to the reference voltage application terminal 14. When the voltage applied to the anode electrode of the PIN diode 10 from the DC voltage application terminal 3 through the DC network 15 and the RF choke coil 12 is −5V to 0V, the reference voltage application terminal 14 has the anode of the PIN diode 10. In the voltage range applied to the electrode, −5 V having the maximum absolute value is applied.

  As a result, when the absolute value of the voltage applied to the DC voltage application terminal increases, the potential difference between the anode and cathode of the PIN diode 10 decreases, and the required characteristics can be realized. The DC voltage blocking capacitor 11 is for preventing a constant voltage applied to the DC voltage application terminal 14 from being superimposed on the anode electrode of the varactor diode 7. The DC network 15 is a DC circuit composed of a resistor, an OP (operation) amplifier, or the like, and appropriately converts the voltage applied to the DC voltage application terminal 3 and is plotted with triangles in FIG. This is for realizing desired PIN diode characteristics.

  The resistance value Ra ′ of the resistor 9 is derived from the equation (2) described later, where Z0 is the characteristic impedance of the phase shifter body and Rs ′ is the equivalent series resistance value in series connection of the varactor diode 7 and the PIN diode 10. It is a value to be. In the circuit configuration shown in FIG. 2, the reflection coefficient at the high-frequency signal input terminal 1 is shown in FIGS. As seen from this, the locus of the reflection coefficient on the Smith chart moves concentrically with respect to the center of the Smith chart, and the reflection loss characteristic with respect to the capacitance change between the terminals of the varactor diode 7 is also constant (in this example, 0.7 dB). It turns out that it is.

  Referring to FIG. 1 again, a circuit configuration of the reflection type phase shifter proposed this time is shown. High-frequency signal input terminal 1, high-frequency signal output terminal 2, DC voltage terminal 3 for applying a DC voltage for changing the inter-terminal capacitance of the variable capacitance element, DC voltage blocking capacitors 4a and 4b, and RF choke coil 5a and 5b, a 90-degree 3 dB hybrid 6 for synthesizing the high-frequency signals phase-shifted by the capacitance change between the terminals of the variable capacitance element, and making the high-frequency signal input terminal 1 and the high-frequency signal output terminal 2 independent, and variable A dc voltage is applied to the varactor diodes 7a and 7b as the capacitive elements, the resistors 9a and 9b for suppressing the change in the return loss of the varactor diode due to the change in the capacitance between the terminals of the varactor diode, DC voltage blocking capacitors 8a and 8b, and the capacitance change between terminals of the varactor diode The PIN diodes 10a and 10b, the DC voltage blocking capacitors 11a and 11b, the RF choke coils 12a, 12b, 13a and 13b, the reference voltage application terminal 14, and the PIN diode for suppressing the Rs change of the varactor diode And a DC network 15 for optimizing the DC voltage applied to the.

  For the description of the operation of the embodiment, the operation will be described with reference to the circuit configuration of FIG. High-frequency signal input terminal 1, DC voltage terminal 3 for applying a DC voltage for changing the inter-terminal capacitance of the variable capacitance element, DC voltage blocking capacitor 4, RF choke coil 5, varactor diode 7 as a variable capacitance element, varactor A resistor 9 for suppressing a change in the return loss of the varactor diode accompanying a change in capacitance between the terminals of the diode, a DC voltage blocking capacitor 8 for preventing a DC voltage from being applied to the resistor 9, and a terminal of the varactor diode Optimizes the DC voltage applied to the PIN diode 10, the DC voltage blocking capacitor 11, the RF choke coils 12 and 13, the reference voltage application terminal 14, and the PIN diode for canceling the Rs change of the varactor diode due to the capacitance change A DC network 15 for this is shown.

  Here, as the DC voltage blocking capacitors 4, 8, and 11, capacitors having a sufficiently low impedance at the signal frequency to be used are used. Either the anode electrode or the cathode electrode of the varactor diode 7 (in this example, the cathode electrode) is grounded, and the other electrode (in this example, the anode electrode) is applied to the DC voltage application terminal 3. The A reverse bias voltage (in this example, a negative voltage) for changing the inter-terminal capacitance of the varactor diode 7 is applied through the RF choke coil 5.

  By changing the reverse bias voltage, the capacitance between the terminals of the varactor diode is changed. The phase change of the signal is realized by changing the reflection impedance of the varactor diode by changing the capacitance between terminals. The PIN diode 10 is connected in series on the anode electrode side of the varactor diode 7 with the DC voltage blocking capacitor 11 interposed therebetween. A variable voltage (in this example, a negative voltage) for changing the inter-terminal capacitance of the varactor diode 7 applied to the DC voltage application terminal 3 is connected to the anode electrode of the PIN diode 10 by the DC circuit network 15 and the RF choke. Applied through the coil 12.

  A constant DC voltage applied to the reference voltage application terminal 14 is applied to the cathode electrode of the PIN diode through the RF choke coil 13. In FIG. 3, the state of change of Rs of the varactor diode 7 when the absolute value of the voltage applied to the DC voltage application terminal 3 is changed is plotted with rhombus marks. On the other hand, what is plotted with triangle marks is the desired PIN diode characteristics. Since the varactor diode 7 and the PIN diode 10 are connected in series, the combined resistance value is simply added, that is, at the DC voltage application terminal 3 as indicated by a cross in FIG. A certain characteristic is exhibited with respect to the applied voltage change.

  Here, as shown in FIG. 3, the PIN diode 10 is required to have a characteristic that the resistance value decreases as the voltage applied to the DC voltage application terminal 3 increases. However, the PIN diode 10 alone exhibits the reverse characteristic that the resistance value decreases as the forward bias voltage increases. In order to solve this, a constant DC voltage is applied to the reference voltage application terminal 14. Here, for example, when the variable voltage applied to the anode electrode of the PIN diode 10 is −5 to 0V, −5V having the maximum absolute value within the range is applied to the reference voltage application terminal 14.

  As a result, when the absolute value of the voltage applied to the DC voltage application terminal increases, the potential difference between the anode and the cathode of the PIN diode 10 decreases, that is, the resistance increases as the voltage applied to the DC voltage application terminal 3 increases. The desired property of decreasing value can be obtained.

  The DC voltage blocking capacitor 11 is for preventing a constant voltage applied to the DC voltage application terminal 14 from being superimposed on the anode electrode of the varactor diode 7. The direct current network 15 is a direct current network composed of a resistor, an OP amplifier, or the like, converts a variable voltage applied to the direct current voltage application terminal 3, and has a desired PIN diode characteristic plotted with triangles in FIG. It is for realizing.

The resistance value Ra ′ of the resistor 9 is derived from the equation (2), where Z0 is the characteristic impedance of the phase shifter body and Rs ′ is the equivalent series resistance value in series connection of the varactor diode 7 and the PIN diode 10. It is a value.
Ra '= Z0 [1 + √ {1 + 4 (Rs' / Z0) ² }] / (2Rs' / Z0)
(2)

  In the circuit configuration shown in FIG. 2, the simulation result of the reflection coefficient at the high-frequency signal input terminal 1 with the inter-terminal capacitance of the varactor diode 7 varied is shown in FIGS. As seen from this, the locus of the reflection coefficient on the Smith chart moves on a concentric circle with respect to the center of the Smith chart, and the reflection loss characteristic with respect to the capacitance change between the terminals of the varactor diode 7 is also constant (in this example, 0.7 dB). ).

  By using two sets of elements such as the PIN diode and the varactor diode described above and connecting them by a 90 ° 3 dB hybrid 6, the reflection type phase shifter proposed this time as shown in FIG. 1 can be configured. A signal input from the high-frequency signal input terminal 1 passes through a DC voltage blocking capacitor 4a, and by a 90 degree 3 dB hybrid 6, a PIN diode 10a, DC voltage blocking capacitors 8a and 11a, a varactor diode 7a, an RF choke coil 5a, 12a and 13a and the resistor 9a, and the PIN diode 10b, the DC voltage blocking capacitors 8b and 11b, the varactor diode 7b, the RF choke coils 5b, 12b and 13b, and the resistor 9b.

  The signals phase-shifted in each route are again synthesized by the 90 ° 3 dB hybrid 6, passed through the DC voltage blocking capacitor 4 b, and output from the high frequency signal output terminal 2. At this time, the signal output from the high-frequency signal output terminal 2 becomes substantially constant without variation in passing loss when the phase is changed by a change in voltage applied to the DC voltage application terminal 3.

  With the above configuration and operation, a change in the equivalent series resistance value of the varactor diode due to a change in the capacitance between terminals can be suppressed, and a variation in the passage loss of the reflective phase shifter can be reduced when the phase changes.

  As an embodiment of the present invention, application to a reflection type phase shifter using a 90 ° 3 dB hybrid is mentioned. As shown in FIG. 5, a reflection type using a circulator 16 instead of the 90 ° 3 dB hybrid 6 is used. It can also be applied to a phase shifter. In FIG. 5, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals.

It is a circuit diagram of one embodiment of the present invention. It is the figure which extracted and showed a part of FIG. It is a figure which shows the example of a characteristic of the equivalent series resistance versus bias voltage (voltage of the terminal 3 of FIG. 2) absolute value of a varactor diode and a PIN diode. It is a figure which shows the simulation result at the time of changing the capacity | capacitance between terminals of a varactor diode of the reflection coefficient in the high frequency input terminal 1. FIG. It is a circuit diagram of other embodiments of the present invention. It is a circuit diagram for demonstrating a prior art example. It is the figure which extracted and showed a part of FIG. It is the figure which showed the locus | trajectory of the reflection coefficient in the high frequency signal input terminal 1 as a Smith chart when changing the capacity | capacitance between terminals of a varactor diode. It is a circuit diagram for demonstrating another conventional example. It is a figure which shows the example of a characteristic of the capacity | capacitance between Rs versus terminals of a varactor diode. It is a figure which shows the result of having simulated the reflection coefficient of the varactor diode single-piece | unit.

Explanation of symbols

1 High frequency input terminal
2 High frequency output terminal
3 Bias terminal 4, 8, 11 Capacitor 5, 12, 13 Choke coil
6 Hybrid circuit
7 Varactor diode
9 Resistance
10 PIN diode
15 DC network
16 Circulator

Claims (6)

A phase shifter comprising: a varactor diode as a variable capacitance element; and a hybrid for synthesizing a signal phase-shifted due to a change in capacitance of the varactor diode and isolating the signal input / output terminals.
A phase shifter comprising a PIN diode connected in series to the varactor diode and canceling a resistance change caused when the capacitance of the varactor diode changes.   2. A DC network that further generates a forward bias voltage for the PIN diode in response to a reverse bias voltage applied to the varactor diode to change the capacitance of the varactor diode. The phase shifter described.   The phase shifter according to claim 1, further comprising a resistor that suppresses a change in return loss associated with a change in capacitance of the varactor diode.   The phase shifter according to claim 1, wherein a circulator is used instead of the hybrid. A varactor diode as a variable capacitance element, a hybrid for synthesizing a signal phase-shifted due to a change in capacitance of the varactor diode and isolating between signal input / output terminals, and connected in series to the varactor diode A phase shifter control method including a PIN diode that cancels a resistance change caused by a change in capacitance of a varactor diode,
Generating a forward bias voltage that changes with respect to the PIN diode in response to a change in a reverse bias voltage applied to the varactor diode in order to change the capacitance of the varactor diode; Control method.   6. The method of controlling a phase shifter according to claim 5, wherein a circulator is used instead of the hybrid.

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