Digital variable reactance elements, phase shifters, and impedance matching circuits

Abstract

Provided is a digital variable reactance element that has a wide variable width. A digital variable reactance element 1 comprises a plurality of digital capacitors 2 and a plurality of digital inductors 4. The plurality of digital capacitors 2 and the plurality of digital inductors 4 are connected in series or in parallel. Each of the plurality of digital capacitors 2 has a capacitor C1 and a first digital switch Q that are connected in series or in parallel, and the first digital switch Q can be switched between two states, which are an on-state and an off-state. Each of the plurality of digital inductors 4 has an inductor L1 and a second digital switch Q that are connected in series or in parallel, and the second digital switch Q can be switched between two states, which are an on-state and an off-state.

Description

Technical Field

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[0001] The present invention relates to a digital variable reactance element, a phase shifter, and an impedance matching circuit.

Background Art

[0002] For example, in a phase shifter used in a microwave circuit, a variable reactance element is used. As such a variable reactance element, variable capacitors such as a variable capacitor, a varicap, or a varactor diode are known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the frequency f is high, as in a high-frequency phase shifter, the phase shift width of the phase shifter becomes small and the loss becomes large. Therefore, a variable reactance element having a larger variable width of reactance (1 / 2πfc) is required.​​​​​​​As shown in the Smith chart in Figure 8, when a capacitor is inserted or its capacitance increases, the reactance (impedance) changes in the direction of the arrow D_C. On the other hand, when an inductor is inserted or its inductance increases, the reactance (impedance) changes in the direction of the arrow D_L. Thus, the change in reactance due to a variable capacitor and the change in reactance due to a variable inductor are unidirectional changes that are different from each other.

[0007] Therefore, to control a wider range of reactance variation, it was necessary to use multiple variable capacitors or multiple variable inductors, and the control signals for these multiple variable capacitors or multiple variable inductors were complex.

[0008] Therefore, the present invention aims to provide a digital variable reactance element with a wide variable range, a phase shifter, and an impedance matching circuit. [Means for solving the problem]

[0009] The digital variable reactance element according to the present invention is a digital variable reactance element that digitally varies its reactance, and comprises a plurality of digital capacitors and a plurality of digital inductors. The plurality of digital capacitors and the plurality of digital inductors are connected in series or in parallel. Each of the plurality of digital capacitors has a capacitor connected in series or in parallel and a first digital switch, and the first digital switch is switchable between two states: on and off. Each of the plurality of digital inductors has an inductor connected in series or in parallel and a second digital switch, and the second digital switch is switchable between two states: on and off.

[0010] The phase shifter according to the present invention includes the above-mentioned digital variable reactance element and generates an output signal in which the phase of the input signal is digitally varied.

[0011] The impedance matching circuit according to the present invention includes the above-mentioned digital variable reactance element and matches the characteristic impedance with respect to the connected transmission line. [Effects of the Invention]

[0012] According to the present invention, the variable range of a digital variable reactance element can be widened. Furthermore, according to the present invention, the phase shift range of a phase shifter can be widened. Furthermore, according to the present invention, the matching range of an impedance matching circuit can be widened. [Brief explanation of the drawing]

[0013] [Figure 1] This is a circuit diagram showing a digital variable reactance element according to this embodiment. [Figure 2] This is a circuit diagram showing a digital variable reactance element according to a modified example 1 of this embodiment. [Figure 3] This is a circuit diagram showing a digital variable reactance element according to a modified example 2 of this embodiment. [Figure 4] This is a circuit diagram showing an example of a phase shifter according to this embodiment. [Figure 5] This is a circuit diagram showing another example of a phase shifter according to this embodiment. [Figure 6] This figure shows an example of the design of a phase shifter, as shown in Figure 4. [Figure 7] This is a circuit diagram showing an example of an impedance matching circuit according to this embodiment. [Figure 8] This is a Smith chart illustrating an example of reactance characteristics. [Modes for carrying out the invention]

[0014] Hereinafter, an example of an embodiment of the present invention will be described with reference to the attached drawings. In each drawing, the same or corresponding parts will be denoted by the same reference numerals.

[0015] (Digital variable reactance element of this embodiment) FIG. 1 is a circuit diagram showing a digital variable reactance element according to the present embodiment. As shown in FIG. 1, the digital variable reactance element 1 is an element that variably changes reactance in a digital manner. The digital variable reactance element 1 includes a plurality of digital capacitors 2 and a plurality of digital inductors 4. The digital variable reactance element 1 may include a digital resistor 6. In the digital variable reactance element 1, the plurality of digital capacitors 2, the plurality of digital inductors 4, and the digital resistor 6 are connected in parallel.

[0016] The digital capacitor 2 has a capacitor C1 and a digital switch (first digital switch) Q connected in series. The digital switch Q is not particularly limited, but a switch element such as a FET (Field Effect Transistor) is used. The digital switch Q can be switched between two states: an on state and an off state. Thereby, the digital capacitor 2 can be switched between two values: a first value that is the capacitance of the capacitor C1 (when the digital switch Q is in the on state), and a second value that is a capacitance of 0 (when the digital switch Q is in the off state). That is, the digital capacitor 2 can switch its capacitance in a digital manner.

[0017] The digital inductor 4 has an inductor L1 and a digital switch (second digital switch) Q connected in series. The digital switch Q is not particularly limited, but a switch element such as a FET (Field Effect Transistor) is used. The digital switch Q can be switched between two states: an on state and an off state. Thereby, the digital inductor 4 can be switched between two values: a first value that is the inductance of the inductor L1 (when the digital switch Q is in the on state), and a second value that is an inductance of 0 (when the digital switch Q is in the off state). That is, the digital inductor 4 can switch its inductance in a digital manner.

[0018] The digital resistor 6 has a resistor R1 and a digital switch Q connected in series. The digital switch Q is not particularly limited, but a switching element such as a FET (Field Effect Transistor) is used. The digital switch Q can be switched between two states: an on state or an off state. As a result, the digital resistor 6 can be switched between two values: a first value which is the resistance value of resistor R1 (when the digital switch Q is in the on state), or a second value which is a resistance value of 0 (when the digital switch Q is in the off state). That is, the digital resistor 6 can switch its resistance value digitally.

[0019] As a result, the variable reactance element 1 can vary its reactance digitally by switching the on state or the off state of each digital switch Q. Also, the variable reactance element 1 can vary its impedance, particularly the impedance with respect to an RF signal (high-frequency signal), digitally by switching the on state or the off state of each digital switch Q.

[0020] As described above, according to the digital variable reactance element 1 of the present embodiment, the reactance by the plurality of capacitors C1 and the plurality of inductors L1 is variably controlled digitally by the digital switch Q. Also, according to the digital variable reactance element 1, the impedance by the plurality of capacitors C1, the plurality of inductors L1 and the resistor R1 is variably controlled digitally by the digital switch Q.

[0021] Also, not only the capacitance can be varied but also the inductance can be varied, and the reactance can be widely varied from capacitive (1 / 2πfc) to inductive (2πfL). Therefore, the variable range of the reactance (1 / 2πfc + 2πfL) can be widened.

[0022] Furthermore, it does not require the use of multiple variable capacitors or multiple variable inductors, and the control signals for multiple variable capacitors or multiple variable inductors do not become complex.

[0023] Furthermore, it becomes possible to realize a low-loss, high-frequency (RF) phase shifter with a large phase shift range.

[0024] In the embodiment described above, a variable reactance element 1 was illustrated in which each digital capacitor 2 has a capacitor C1 connected in series and a digital switch Q, each digital inductor 4 has an inductor connected in series or in parallel and a digital switch, and a plurality of digital capacitors 2 and a plurality of digital inductors 4 are connected in parallel. However, the present invention is not limited thereto and is applicable to various variable reactance elements in which each digital capacitor has a capacitor connected in series or in parallel and a digital switch, each digital inductor has an inductor connected in series or in parallel and a digital switch, and a plurality of digital capacitors and a plurality of digital inductors are connected in series or in parallel. For example, modified examples 1 and 2 of this embodiment are illustrated below.

[0025] (Digital variable reactance element of modified example 1) Figure 2 is a circuit diagram showing a digital variable reactance element according to Modification 1 of this embodiment. As shown in Figure 2, the digital variable reactance element 1A is an element that digitally varies its reactance. The digital variable reactance element 1A comprises a plurality of digital capacitors 2A and a plurality of digital inductors 4A. The digital variable reactance element 1A may also include a digital resistor 6A. In the digital variable reactance element 1A, the plurality of digital capacitors 2A, the plurality of digital inductors 4A, and the digital resistor 6A are connected in series.

[0026] The digital capacitor 2A has a capacitor C1 connected in series with a digital switch (first digital switch) Q, and a capacitor C2 connected in parallel with the same digital switch Q. Specifically, in the digital capacitor 2A, the series circuit of capacitor C1 and digital switch Q and capacitor C2 are connected in parallel. The digital switch Q is the same as described above. As a result, the digital capacitor 2A can switch between two values: a first value which is the combined capacitance of capacitors C1 and C2 (digital switch Q is on), and a second value which is the capacitance of capacitor C2 (digital switch Q is off). In other words, the digital capacitor 2A can switch its capacitance digitally.

[0027] The digital inductor 4A has an inductor L1 and a digital switch (second digital switch) Q connected in series, and an inductor L2 and the same digital switch Q connected in parallel. Specifically, in the digital inductor 4A, the series circuit of inductor L1 and digital switch Q and inductor L2 are connected in parallel. The digital switch Q is the same as described above. As a result, the digital inductor 4A can switch between two values: a first value which is the combined inductance of inductors L1 and L2 (digital switch Q is ON), and a second value which is the inductance of inductor L2 (digital switch Q is OFF). In other words, the digital inductor 4A can switch its inductance digitally.

[0028] The digital resistor 6A has a resistor R1 and a digital switch Q connected in parallel. The digital switch Q is the same as described above. As a result, the digital resistor 6A can switch between two values: a first value with a resistance of 0 (digital switch Q is on), and a second value with the resistance of resistor R1 (digital switch Q is off). In other words, the digital resistor 6A can switch its resistance value digitally.

[0029] As a result, the variable reactance element 1A can have its reactance digitally varied by switching the on or off state of each digital switch Q. Furthermore, the variable reactance element 1A can digitally vary its impedance, particularly the impedance to RF signals (high-frequency signals), by switching the on or off state of each digital switch Q.

[0030] The digital variable reactance element 1A of this modified example 1 also has the same advantages as the digital variable reactance element 1 of this embodiment described above.

[0031] (Digital variable reactance element of modified example 2) Figure 3 is a circuit diagram showing a digital variable reactance element according to a modified example 2 of this embodiment. As shown in Figure 3, the digital variable reactance element 1B is an element that digitally varies its reactance. The digital variable reactance element 1B comprises a plurality of the above-described digital capacitors 2A and a plurality of the above-described digital inductors 4. In the digital variable reactance element 1B, the plurality of digital capacitors 2A are connected in series, the plurality of digital inductors 4 are connected in parallel, and the series circuit of the digital capacitors 2A and the parallel circuit of the digital inductors 4 are connected in series.

[0032] As a result, the variable reactance element 1B can have its reactance digitally varied by switching the on or off state of each digital switch Q. Furthermore, the variable reactance element 1B allows for digital variation of the impedance, particularly the impedance to RF signals (high-frequency signals), by switching the on or off state of each digital switch Q.

[0033] This modified example 2, the digital variable reactance element 1B, also has the same advantages as the digital variable reactance element 1 of this embodiment described above.

[0034] In the following, a phase shifter and an impedance matching circuit will be described as examples of devices to which the above-described digital variable reactance element is applied. Note that the digital variable reactance element in this embodiment is not limited to these examples, and can be applied to various devices requiring variable reactance or impedance, such as variable loads, detection circuits for MRI (Magnetic Resonance Imaging), VCOs (Voltage Controlled Oscillators), phase-locked circuits, and frequency synthesizers.

[0035] (Phase shifter of this embodiment) Figure 4 is a circuit diagram showing an example of a phase shifter according to this embodiment, and Figure 5 is a circuit diagram showing another example of a phase shifter according to this embodiment. The phase shifter 10 shown in Figure 4 is a hybrid-coupled high-frequency (RF) phase shifter composed of quarter-wavelength lines 11 and 12 with characteristic impedance Z0 and quarter-wavelength lines 13 and 14 with characteristic impedance Z0 / √2. The phase shifter 10 has one end of line 11 as the input terminal RF_IN and the other end of line 11 as the output terminal RF_OUT. The phase shifter 10 includes the variable reactance elements 1 (1A, 1B) described above which terminate the output terminal 13_OUT on the line 13 side and the output terminal 14_OUT on the line 14 side, respectively.

[0036] In the phase shifter 10, the RF signal input from the input terminal RF_IN is distributed through hybrid-coupled transmission lines 11, 12, 13, and 14, and transmitted to the output terminal 13_OUT on the line 13 side and the output terminal 14_OUT on the line 14 side. Since these output terminals 13_OUT and 14_OUT are terminated by the variable reactance elements 1 (1A, 1B) described above, the signals transmitted to these output terminals undergo a phase shift dependent on the reactance amount of the variable reactance elements 1 (1A, 1B) and are reflected. The signals reflected at these output terminals 13_OUT and 14_OUT are combined again in the hybrid-coupled transmission lines 11, 12, 13, and 14 and output from the output terminal RF_OUT. At this time, the output signal undergoes a phase shift dependent on the reactance amount of the variable reactance element 1 (1A, 1B) described above, and by changing the reactance amount of the variable reactance element, it operates as a phase shifter.

[0037] In Figure 4, an example is shown in which the above-described variable reactance elements 1(1A,1B) are applied to a hybrid-coupled phase shifter 10. However, as shown in Figure 5, the above-described variable reactance elements 1(1A,1B) may also be applied to a loaded-line phase shifter 10 composed of a quarter-wavelength transmission line 11 with a characteristic impedance of Z0.

[0038] Figure 6 shows an example design of the phase shifter shown in Figure 4. In Figure 6, the phase shift amount ps of the phase shifter shown in Figure 4 was measured using a network analyzer while varying the capacitance C of the digital capacitor or the inductance L of the digital inductor. As shown in Figure 6, a phase shift characteristic of approximately 360° was obtained. Thus, with the high-frequency phase shifter using the digital variable reactance element of the embodiment described above, the reactance can be broadly varied in both capacitive and inductive ways, making it possible to realize a low-loss high-frequency (RF) phase shifter with a large phase shift range.

[0039] (The matching circuit of this embodiment) Figure 7 is a circuit diagram showing an example of an impedance matching circuit according to this embodiment. The impedance matching circuit 20 shown in Figure 7 comprises an inductor 21 connected in series between one of a pair of input terminals RF_IN+ and RF_IN-, which is the input terminal RF_IN+, and one of a pair of output terminals RF_OUT+ and RF_OUT-, which is the output terminal RF_OUT+, and the variable reactance elements 1 (1A, 1B) described above, connected between the pair of input terminals RF_IN+ and RF_IN-, and between the pair of output terminals RF_OUT+ and RF_OUT-, respectively.

[0040] The impedance matching circuit 20 operates as an impedance matching circuit by changing the impedance amount of the variable reactance elements 1 (1A, 1B) described above.

[0041] Thus, with the impedance matching circuit using the digital variable reactance element of the above-described embodiment, the reactance can be broadly varied in both capacitive and inductive ways, making it possible to realize an impedance matching circuit with low loss and a large impedance adjustment range.

[0042] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications and variations are possible. [Explanation of symbols]

[0043] 1,1A,1B Digital Variable Reactance Element 2.2A Digital Capacitor 4.4A Digital Inductor 6.6A Digital Resistor C1, C2 Capacitors L1, L2 Inductors R1 resistor Q Digital Switch 10 phase shifter 20 Impedance Matching Circuit

Claims

1. A digital variable reactance element that digitally varies the reactance, Multiple digital capacitors, Multiple digital inductors, Equipped with, The aforementioned plurality of digital capacitors and the plurality of digital inductors are connected in series. Each of the aforementioned plurality of digital capacitors has a first series circuit consisting of a first capacitor and a first digital switch, and a second capacitor connected in parallel to the first series circuit, and the first digital switch is switchable between two states: on and off. Each of the aforementioned plurality of digital inductors has a second series circuit consisting of a first inductor and a second digital switch, and a second inductor connected in parallel to the second series circuit, and the second digital switch is switchable between two states: on and off. Digital variable reactance element.

2. The digital variable reactance element described in claim 1 is provided, It generates an output signal in which the phase of the input signal is digitally varied. Phase shifter.

3. The digital variable reactance element described in claim 1 is provided, Match the characteristic impedance to the connected transmission line. Impedance matching circuit.

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