Transmission circuit

Abstract

This transmission circuit includes: a plurality of impedance circuits that each have a different impedance; a plurality of switching elements that are each connected to one of the plurality of impedance circuits; and a control circuit that is configured so as to control the opening and closing of the plurality of switching elements. The control circuit is configured to be able to perform control so as to selectively change the opening and closing of the plurality of switching elements, and rotate a reflection coefficient of an antenna-side output terminal in a complex plane, along a circle that is warped in comparison to a perfect circle.

Description

[Technical field]

[0001] The present disclosure relates to a transmission circuit. [Background technology]

[0002] A backscattering method is known as a data communication method for wireless communication devices. For example, Patent Document 1 discloses a technique for realizing a single sideband by suppressing either an upper sideband (USB) signal or a lower sideband (LSB) signal using a splitter / combiner. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-323223 A Summary of the Invention

[0004] A transmission circuit according to one embodiment of the present disclosure is a transmission circuit configured to be connected to an antenna, the transmission circuit including a plurality of impedance circuits each having a different impedance, a plurality of switch elements, one of which is connected to each of the plurality of impedance circuits, and a control circuit configured to control the opening and closing of the plurality of switch elements, the control circuit being configured to selectively change the opening and closing of the plurality of switch elements to control the reflection coefficient of an output terminal on the antenna side to rotate on a distorted circle in a complex plane compared to a perfect circle. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a block diagram showing an example of a configuration of a wireless communication device according to an embodiment. [Diagram 2] FIG. 2 is a diagram for explaining a method for controlling the rotation of impedance on a complex plane according to the embodiment. [Figure 3A]FIG. 3A is a diagram for explaining a change in a backscatter signal. [Figure 3B] FIG. 3B is a diagram for explaining a change in the backscatter signal. [Figure 3C] FIG. 3C is a diagram for explaining a change in the backscatter signal. [Figure 4] FIG. 4 is a diagram illustrating an example of the configuration of a transmission circuit according to the embodiment. [Diagram 5] FIG. 5 is a diagram for explaining a method for controlling the rotation of the reflection coefficient on a complex plane according to the embodiment. [Figure 6] FIG. 6 is a diagram for explaining a control method of a transmission circuit according to a comparative example. [Figure 7] FIG. 7 is a diagram for explaining a control method of the transmission circuit according to the embodiment. [Figure 8] FIG. 8 is a diagram for explaining a method for rotating and controlling the impedance of the output terminal on the antenna side of the transmission circuit according to the embodiment. [Figure 9] FIG. 9 is a diagram showing an example of a spectral waveform of a backscattering signal according to a comparative example. [Figure 10] FIG. 10 is a diagram illustrating an example of a spectral waveform of a backscattering signal according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Note that the present disclosure is not limited to these embodiments, and when there are multiple embodiments, the present disclosure also includes a configuration in which each embodiment is combined. In the following embodiments, the same parts are denoted by the same reference numerals, and duplicated descriptions are omitted.

[0007] [Embodiment] The configuration of a wireless communication device according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing an example of the configuration of a wireless communication device according to an embodiment.

[0008] 1, the wireless communication device 1 includes an antenna 10, a BPF (Band Pass Filter) 11, an RFBS (Radio Frequency Back Scatter) device 20, a control device 30, and a sensor 40. The wireless communication device 1 is a communication device configured to perform wireless communication using a backscatter method such as RFID.

[0009] The antenna 10 is configured to receive a signal transmitted to the wireless communication device 1. The antenna 10 is configured to transmit radio waves toward the outside of the wireless communication device 1. The BPF 11 is a filter configured to pass a signal in a desired frequency band.

[0010] The RFBS device 20 includes a high frequency switch 21, an amplifier 22, a demodulator 23, an oscillator 24, an LPF (Low Pass Filter) 25, an LPF 26, a control circuit 27, and a transmission circuit 28. The RFBS device 20 is a wireless communication device that supports backscattering data communication. In backscattering data communication, communication is performed by utilizing the reflection of transmitted radio waves.

[0011] The high frequency switch 21 is configured to switch the connection between the antenna 10 and a transmission circuit system or a reception circuit system. The high frequency switch 21 is configured to be able to connect the transmission circuit system to the antenna 10. The wireless communication device 1 is configured to transmit when the antenna 10 is connected to the transmission circuit system. The high frequency switch 21 is configured to be able to connect the reception circuit system to the antenna 10. The transmission circuit system includes an oscillator 24, an LPF 25, an LPF 26, a control circuit 27, and a transmission circuit 28. The reception circuit system includes an amplifier 22 and a demodulator 23.

[0012] The amplifier 22 is configured to amplify and output a signal received from the antenna 10. The amplifier 22 is configured to output the amplified signal to the demodulation unit 23. The demodulation unit 23 is configured to perform demodulation processing on the input signal. The demodulation unit 23 is configured to demodulate the signal received from the amplifier 22. For example, the demodulation unit 23 is configured to perform demodulation processing on the signal received from the amplifier 22 (a modulated signal such as ASK (Amplitude Shift Keying)).

[0013] The control device 30 is realized, for example, by a processor or the like executing a program stored therein using a RAM (Random Access Memory) or the like as a working area. The control device 30 may be a controller. The control device 30 may be realized, for example, by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control device 30 may be realized by a combination of software and hardware.

[0014] The control device 30 is configured to output serial data S1 to the control circuit 27 via the LPF 25. The serial data S1 is based on output data from the sensor 40. The control device 30 outputs serial data S2 to the control circuit 27 via the LPF 26. The serial data S2 is based on output data from the sensor 40. The serial data S1 has a phase difference of approximately 90° with respect to the serial data S2.

[0015] The control device 30 is configured to output a control signal S3 to the control circuit 27. The control signal S3 can be used to suppress either the USB signal or the LSB signal relative to the carrier signal. The control device 30 is configured to output a control signal S4 to the oscillator 24. The control signal S4 can be used to control a channel used for communication.

[0016] The sensor 40 is configured to detect various physical quantities. There is no particular limit to the physical quantities detected by the sensor 40. The sensor 40 may include, for example, one or both of a temperature sensor configured to detect the temperature around the wireless communication device 1 and an acceleration sensor configured to detect acceleration occurring in the wireless communication device 1. The sensor 40 may include other sensors.

[0017] The oscillator 24 is configured to generate an oscillation signal of a predetermined frequency. The oscillator 24 is configured to generate an oscillation signal S5 in accordance with a control signal S4. The oscillator 24 is configured to generate an oscillation signal S6 that is 90° out of phase with the oscillation signal S5.

[0018] The control circuit 27 is configured to control the transmission circuit 28. The control circuit 27 is configured to control the transmission circuit 28 so as to adjust the impedance value of the transmission circuit 28 based on the serial data S1, the serial data S2, and the control signal S3. The control circuit 27 is configured to change the impedance of the transmission circuit 28. Due to the change in impedance, the reflection coefficient of the output terminal on the antenna 10 side rotates in the complex plane. The control circuit 27 is configured to change the impedance of the transmission circuit 28 and control the reflection coefficient of the output terminal to rotate in the complex plane. For example, the control circuit 27 is configured to control the impedance of the transmission circuit 28 so as to reduce the USB signal or LSB signal relative to the carrier signal in the reflected signal (hereinafter also referred to as the backscatter signal) to realize a single sideband.

[0019] A method in which the control circuit 27 controls the reflection coefficient of the output terminal of the transmission circuit 28 on the antenna 10 side so as to rotate on the complex plane of the polar chart will be described using the polar chart (polar coordinates) in Fig. 2. Fig. 2 is a diagram for explaining a method in which the control circuit 27 changes the impedance of the transmission circuit 28 and controls so as to rotate the reflection coefficient of the output terminal.

[0020] Figure 2 shows the change in reflection coefficient Γ due to the change in impedance on a polar chart. Impedance is calculated by the following formula (1). In formula (1), Z is impedance, R is resistance, j is an imaginary number, ω is angular frequency, L is inductance, and C is capacitance. Z = R + j(ωL-1 / ωC) (1)

[0021] The reflection coefficient Γ can be expressed by the following equation: Γ=(Z-Z0) / (Z+Z0) (2) Here, Z0 is the impedance of the antenna 10 or the BPF 11.

[0022] The control circuit 27 selects and controls the impedance Z to control the reflection coefficient Γ to rotate around a reference point. The reference point includes the origin, but is not limited to the origin, and includes any point. The closer the reference point is to the origin, the more likely it is that the transmission circuit will obtain a signal that is closer to the ideal. The more the transmission circuit is controlled to rotate in a circle around the reference point, the more likely it is that the signal will be closer to the ideal. In terms of a Smith chart, the lower semicircular area indicates capacitive properties, and the upper half indicates inductive properties. Changes on the real axis represent changes in resistance value.

[0023] The control circuit 27 can selectively control a plurality of impedances included in the transmission circuit 28. For example, the control circuit 27 is configured to control the impedance of the transmission circuit 28 in increments of 45°, i.e., 0°, 45°, 90°, 135°, 180°, −135°, −90°, and −45°. The control circuit 27 is configured to be able to control the impedance of the transmission circuit 28 to rotate discretely by sequentially changing the impedance. The control circuit 27 causes the reflection coefficient Γ to rotate discretely in response to the discrete rotation of the impedance.

[0024] The control circuit 27 is configured to be able to change the impedance in a counterclockwise direction by changing the impedance of the transmission circuit 28. The control circuit 27 is configured to be able to change the reflection coefficient Γ in a counterclockwise direction by rotating the impedance in a counterclockwise direction. When the control of the reflection coefficient is in a counterclockwise direction, the reflected signal for the RF (Radio Frequency) is only a USB (Upper Side Band) signal. When the control is performed so that the reflection coefficient is in a clockwise direction, only a LSB (Lower Side Band) signal is obtained. At that time, the frequency of the reflected signal is a frequency detuned by the rotation speed frequency from the RF signal frequency. Using FIG. 3A, FIG. 3B, and FIG. 3C, some examples of changes in the backscatter signal caused by changing the impedance and controlling the reflection coefficient will be described.

[0025] FIG. 3A is a diagram showing a frequency spectrum for explaining the state of a backscatter signal when the control circuit 27 controls only the resistance component of the impedance and changes the reflection coefficient Γ on the real axis of the polar chart (FIG. 2). The horizontal axis shows frequency, and the vertical axis shows the intensity of the RF signal and the reflected signal. FIG. 3A shows a carrier signal 51, a USB signal 52, and an LSB signal 53. When the resistance component is controlled, the reflection coefficient Γ is controlled to either 0° or 180° on the real axis. When the reflection coefficient Γ is controlled by changing the impedance only with the resistance component, as shown in FIG. 3A, for example, when switching from 0° to 180°, a right-handed signal component and a left-handed signal component are inherent. Due to the existence of signal components of two rotation directions, the USB signal 52 and the LSB signal 53 appear simultaneously, and it is not possible to selectively suppress only one of the signals. As a result, an SSB signal cannot be obtained by controlling only the resistance component.

[0026] FIG. 3B is a diagram showing a frequency spectrum for explaining the change in the backscatter signal when the control circuit 27 changes the inductance / capacitance of the impedance to control the locus of the reflection coefficient Γ to draw a circle. The horizontal axis indicates the frequency, and the vertical axis indicates the intensity of the RF signal and the reflected signal. Based on the formulas (1) and (2), the control circuit 27 can control the impedance to rotate counterclockwise by controlling the value of the inductance. At this time, the impedance rotates counterclockwise, for example, from 0° to 45°, 90°, and 135°. The control circuit 27 can further control the impedance to rotate counterclockwise by controlling the value of the capacitance. At this time, the impedance rotates counterclockwise, for example, from 180° to -135°, -90°, and -45°. As shown in FIG. 3B, the control circuit 27 can reflect the transmitted RF signal so as to suppress the LSB signal 53 by controlling the impedance to rotate counterclockwise. In other words, the control circuit 27 can obtain a backscattered signal converted into SSB in the USB signal 52 by controlling the impedance to rotate counterclockwise.

[0027] FIG. 3C is a diagram showing a frequency spectrum for explaining the change in the backscatter signal when the control circuit 27 changes the capacitance / inductance of the impedance and controls the locus of the reflection coefficient Γ to draw a circle. The horizontal axis indicates the frequency, and the vertical axis indicates the intensity of the RF signal and the reflected signal. Based on the formulas (1) and (2), the control circuit 27 can control the impedance to rotate clockwise by controlling the value of the capacitance. At this time, the impedance rotates clockwise, for example, from 0° to −45°, −90°, and −135°. The control circuit 27 can further control the impedance to rotate clockwise by controlling the value of the inductance. At this time, the impedance rotates clockwise, for example, from 180°, 135°, 90°, and 45°. As shown in FIG. 3C, the control circuit 27 can reflect the transmitted RF signal so as to suppress the USB signal 52 by controlling the impedance to rotate clockwise. In other words, the control circuit 27 can obtain the backscattered signal converted into SSB as the LSB signal 53 by controlling the clockwise rotation of the impedance.

[0028] The transmission circuit 28 is disposed at the front end of the wireless communication device 1. The transmission circuit 28 is a circuit configured to perform backscatter communication in which a transmitted radio wave is reflected as a backscatter signal. The transmission circuit 28 is configured to be connected to the antenna 10. The transmission circuit 28 includes a plurality of impedance circuits each having a different impedance. Each of the plurality of impedance circuits includes a switch element. The switch element is configured to switch the connection of the impedance circuit. The control circuit 27 is configured to switch the connection of the plurality of impedance circuits by controlling the plurality of switch elements. The control circuit 27 is configured to control the impedance of the transmission circuit 28 by controlling the plurality of switch elements.

[0029] [Transmission circuit configuration] The configuration of the transmission circuit according to the embodiment will be described with reference to Fig. 4. Fig. 4 is a diagram showing an example of the configuration of the transmission circuit according to the embodiment.

[0030] As shown in Fig. 4, the transmission circuit 28 includes a capacitor circuit 1201, a capacitor circuit 1202, a capacitor circuit 1203, a capacitor circuit 1204, a capacitor circuit 1205, a capacitor circuit 1206, a capacitor circuit 1207, and a capacitor circuit 1208. The capacitor circuits 1201 to 1208 are each a type of impedance circuit. When it is not necessary to particularly distinguish the capacitor circuits 1201 to 1208, they may be collectively referred to as the capacitor circuit 120. In Fig. 4, components that are less relevant to the present disclosure are omitted.

[0031] The capacitor circuit 1201 includes a signal source 1401, a switch element 1501, and a capacitor C1. The signal source 1401 indicates a signal source to which a control signal is supplied from the control circuit 27. The signal source 1401 is configured to output a control signal to the switch element 1501 to control the opening and closing operation of the switch element 1501. The switch element 1501 has one input terminal connected to the signal source 1401 and the other input terminal connected to a reference potential. The reference potential will be described as being ground, but the present disclosure is not limited thereto. The switch element 1501 is configured to switch between a closed state (on state) and an open state (off state) according to a control signal from the signal source 1401.

[0032] The signal line 101 is electrically connected to one end of the switch element 1501, and one end of the capacitor C1 is electrically connected to the other end. The other end of the capacitor C1 is connected to a reference potential. In this case, the switch element 1501 is configured to electrically connect the signal line 101 and the capacitor C1 when in a closed state. The switch element 1501 is configured to electrically separate the signal line 101 and the capacitor C1 when in an open state. When the signal line 101 and the capacitor C1 are electrically connected, the capacitance value of the capacitor C1 is added to the impedance of the transmission circuit 28. That is, the reactance component of the impedance of the transmission circuit 28 changes when the capacitance value of the capacitor C1 is added.

[0033] The capacitor circuit 1202 includes a signal source 1402, a switch element 1502, and a capacitor C2. The signal source 1402 indicates a signal source to which a control signal is supplied from the control circuit 27. The signal source 1402 is configured to output a control signal to the switch element 1502 to control the opening and closing operation of the switch element 1502. The switch element 1502 has one input terminal connected to the signal source 1402 and the other input terminal connected to a reference potential. The switch element 1502 is configured to switch between a closed state and an open state according to the control signal from the signal source 1402.

[0034] The signal line 101 is electrically connected to one end of the switch element 1502, and one end of the capacitor C2 is electrically connected to the other end. The other end of the capacitor C2 is connected to a reference potential. In this case, the switch element 1502 is configured to electrically connect the signal line 101 and the capacitor C2 when in a closed state. The switch element 1502 is configured to electrically separate the signal line 101 and the capacitor C2 when in an open state. When the signal line 101 and the capacitor C2 are electrically connected, the capacitance value of the capacitor C2 is added to the impedance of the transmission circuit 28. That is, the reactance component of the impedance of the transmission circuit 28 changes when the capacitance value of the capacitor C2 is added.

[0035] The capacitor circuit 1203 includes a signal source 1403, a switch element 1503, and a capacitor C3. The signal source 1403 indicates a signal source to which a control signal is supplied from the control circuit 27. The signal source 1403 is configured to output a control signal to the switch element 1503 to control the opening and closing operation of the switch element 1503. The switch element 1503 has one input terminal connected to the signal source 1403 and the other input terminal connected to a reference potential. The switch element 1503 is configured to switch between a closed state and an open state according to the control signal from the signal source 1403.

[0036] The signal line 101 is electrically connected to one end of the switch element 1503, and one end of the capacitor C3 is electrically connected to the other end. The other end of the capacitor C3 is connected to a reference potential. In this case, the switch element 1503 is configured to electrically connect the signal line 101 and the capacitor C3 when in a closed state. The switch element 1503 is configured to electrically separate the signal line 101 and the capacitor C3 when in an open state. When the signal line 101 and the capacitor C3 are electrically connected, the capacitance value of the capacitor C3 is added to the impedance of the transmission circuit 28. That is, the reactance component of the impedance of the transmission circuit 28 changes when the capacitance value of the capacitor C3 is added.

[0037] The capacitor circuit 1204 includes a signal source 1404, a switch element 1504, and a capacitor C4. The signal source 1404 indicates a signal source to which a control signal is supplied from the control circuit 27. The signal source 1404 is configured to output a control signal to the switch element 1504 to control the opening and closing operation of the switch element 1504. The switch element 1504 has one input terminal connected to the signal source 1404 and the other input terminal connected to a reference potential. The switch element 1504 is configured to switch between a closed state and an open state according to the control signal from the signal source 1404.

[0038] The signal line 101 is electrically connected to one end of the switch element 1504, and one end of the capacitor C4 is electrically connected to the other end. The other end of the capacitor C4 is connected to a reference potential. In this case, the switch element 1504 is configured to electrically connect the signal line 101 and the capacitor C4 when in a closed state. The switch element 1504 is configured to electrically separate the signal line 101 and the capacitor C4 when in an open state. When the signal line 101 and the capacitor C4 are electrically connected, the capacitance value of the capacitor C4 is added to the impedance of the transmission circuit 28. That is, the reactance component of the impedance of the transmission circuit 28 changes when the capacitance value of the capacitor C4 is added.

[0039] The capacitor circuit 1205 includes a signal source 1405, a switch element 1505, and a capacitor C5. The signal source 1405 indicates a signal source to which a control signal is supplied from the control circuit 27. The signal source 1405 is configured to output a control signal to the switch element 1505 to control the opening and closing operation of the switch element 1505. The switch element 1505 has one input terminal connected to the signal source 1405 and the other input terminal connected to a reference potential. The switch element 1505 is configured to switch between a closed state and an open state according to the control signal from the signal source 1405.

[0040] The signal line 101 is electrically connected to one end of the switch element 1505, and one end of the capacitor C5 is electrically connected to the other end. The other end of the capacitor C5 is connected to a reference potential. In this case, the switch element 1505 is configured to electrically connect the signal line 101 and the capacitor C5 when in a closed state. The switch element 1505 is configured to electrically separate the signal line 101 and the capacitor C5 when in an open state. When the signal line 101 and the capacitor C5 are electrically connected, the capacitance value of the capacitor C5 is added to the impedance of the transmission circuit 28. That is, the reactance component of the impedance of the transmission circuit 28 changes when the capacitance value of the capacitor C5 is added.

[0041] The capacitor circuit 1206 includes a signal source 1406, a switch element 1506, and a capacitor C6. The signal source 1406 indicates a signal source to which a control signal is supplied from the control circuit 27. The signal source 1406 is configured to output a control signal to the switch element 1506 to control the opening and closing operation of the switch element 1506. The switch element 1506 has one input terminal connected to the signal source 1406 and the other input terminal connected to a reference potential. The switch element 1506 is configured to switch between a closed state and an open state according to the control signal from the signal source 1406.

[0042] The signal line 101 is electrically connected to one end of the switch element 1506, and one end of the capacitor C6 is electrically connected to the other end. The other end of the capacitor C6 is connected to a reference potential. In this case, the switch element 1506 is configured to electrically connect the signal line 101 and the capacitor C6 when in a closed state. The switch element 1506 is configured to electrically separate the signal line 101 and the capacitor C6 when in an open state. When the signal line 101 and the capacitor C6 are electrically connected, the capacitance value of the capacitor C6 is added to the impedance of the transmission circuit 28. That is, the reactance component of the impedance of the transmission circuit 28 changes when the capacitance value of the capacitor C6 is added.

[0043] The capacitor circuit 1207 includes a signal source 1407, a switch element 1507, and a capacitor C7. The signal source 1407 indicates a signal source to which a control signal is supplied from the control circuit 27. The signal source 1407 is configured to output a control signal to the switch element 1507 to control the opening and closing operation of the switch element 1507. The switch element 1507 has one input terminal connected to the signal source 1407 and the other input terminal connected to a reference potential. The switch element 1507 is configured to switch between a closed state and an open state according to the control signal from the signal source 1407.

[0044] The signal line 101 is electrically connected to one end of the switch element 1507, and one end of the capacitor C7 is electrically connected to the other end. The other end of the capacitor C7 is connected to a reference potential. In this case, the switch element 1507 is configured to electrically connect the signal line 101 and the capacitor C7 when in a closed state. The switch element 1507 is configured to electrically separate the signal line 101 and the capacitor C7 when in an open state. When the signal line 101 and the capacitor C7 are electrically connected, the capacitance value of the capacitor C7 is added to the impedance of the transmission circuit 28. That is, the reactance component of the impedance of the transmission circuit 28 changes when the capacitance value of the capacitor C7 is added.

[0045] The capacitor circuit 1208 includes a signal source 1408, a switch element 1508, and a capacitor C8. The signal source 1408 indicates a signal source to which a control signal is supplied from the control circuit 27. The signal source 1408 is configured to output a control signal to the switch element 1508 to control the opening and closing operation of the switch element 1508. The switch element 1508 has one input terminal connected to the signal source 1408 and the other input terminal connected to a reference potential. The switch element 1508 is configured to switch between a closed state and an open state according to the control signal from the signal source 1408.

[0046] The signal line 101 is electrically connected to one end of the switch element 1508, and one end of the capacitor C8 is electrically connected to the other end. The other end of the capacitor C8 is connected to a reference potential. In this case, the switch element 1508 is configured to electrically connect the signal line 101 and the capacitor C8 when in a closed state. The switch element 1508 is configured to electrically separate the signal line 101 and the capacitor C8 when in an open state. When the signal line 101 and the capacitor C8 are electrically connected, the capacitance value of the capacitor C8 is added to the impedance of the transmission circuit 28. That is, the reactance component of the impedance of the transmission circuit 28 changes when the capacitance value of the capacitor C8 is added.

[0047] The capacitance values ​​of the capacitors C1 to C8 are different from each other. The control circuit 27 is configured to selectively control the switch elements 1501 to 1508. The control circuit 27 is configured to be able to control the reflection coefficient of the output terminal 102 on the antenna 10 side of the transmission circuit 28 to rotate on a complex plane by selectively controlling the switch elements 1501 to 1508. As will be described later, in the present disclosure, the control circuit 27 is configured to be able to selectively change the opening and closing of the switch elements 1501 to 1508 to control the reflection coefficient of the output terminal 102 on the antenna 10 side of the transmission circuit 28 to rotate on a distorted circle compared to a perfect circle on the complex plane.

[0048] Referring to FIG. 5, Complex A method for rotationally controlling the impedance in a complex plane will now be described. Fig. 5 is a diagram for explaining a method for rotationally controlling the reflection coefficient in a complex plane according to an embodiment.

[0049] 5, the transmission circuit 28 shown in FIG 4 may be integrated into an integrated circuit as a capacitor IC 160. In this case, the capacitor IC 160 is configured to be connected to either the phase shifter 170 or the signal line 180 by switching the changeover switch element 190 by the changeover switch control circuit 200.

[0050] The phase shifter 170 includes a capacitor, an inductor, and another capacitor (not shown). The phase shifter 170 is a phase shifter that shifts the phase of an input signal by 90° and outputs the signal.

[0051] The changeover switch control circuit 200 controls the changeover switch element 190 to connect the capacitor IC160 and the signal line 180 when controlling the impedance to rotate between 0° to −90° and between −90° to 180°, for example.

[0052] The changeover switch control circuit 200 controls the changeover switch element 190 to connect the capacitor IC160 and the phase shifter 170 when controlling the impedance to rotate between 0° to 90° and between 90° to 180°.

[0053] 4, the transmission circuit 28 includes eight capacitor circuits 120. Therefore, the changeover switch control circuit 200 can control the position of the impedance on the complex plane to rotate among 16 points by switching the connection between the capacitor IC 160 and the phase shifter 170 and the signal line 180. In this embodiment, the control circuit 27 and the changeover switch control circuit 200 may be integrated together.

[0054] [Transmission circuit control] Next, a method for controlling the transmission circuit 28 shown in FIG. 4 will be described.

[0055] (Control method for comparison) Before describing the embodiment of the present disclosure, a control method of the transmission circuit 28 according to a comparative example will be described with reference to Fig. 6. Fig. 6 is a diagram for explaining a control method of the transmission circuit 28 according to the comparative example.

[0056] Fig. 6 shows the operating state of each switch element included in the transmission circuit 28. Fig. 6 shows waveforms W1, W2, W3, W4, W5, W6, W7, and W8 of the control signals of each switch element.

[0057] A waveform W1 indicates the operating state of the switch element 1501. In the comparative example, the control circuit 27 controls the switch element 1501 so that the switch element 1501 is closed at timing t1 and is open at timing t2.

[0058] A waveform W2 indicates the operating state of the switch element 1502. In the comparative example, the control circuit 27 controls the switch element 1502 so that the switch element 1502 is closed at timing t2 and is open at timing t3.

[0059] A waveform W3 indicates the operating state of switch element 1503. In the comparative example, control circuit 27 controls switch element 1503 so that it is in a closed state at timing t3 and in an open state at timing t4.

[0060] A waveform W4 indicates the operating state of the switch element 1504. In the comparative example, the control circuit 27 controls the switch element 1504 so that the switch element 1504 is closed at timing t4 and is open at timing t5.

[0061] Waveform W5 indicates the operating state of switch element 1505. In the comparative example, control circuit 27 controls switch element 1505 so that it is in a closed state at timing t5 and in an open state at timing t6.

[0062] A waveform W6 indicates the operating state of the switch element 1506. In the comparative example, the control circuit 27 controls the switch element 1506 so that the switch element 1506 is closed at timing t6 and is open at timing t7.

[0063] A waveform W7 indicates the operating state of switch element 1507. In the comparative example, control circuit 27 controls switch element 1507 so that it is in a closed state at timing t7 and in an open state at timing t8.

[0064] A waveform W8 indicates the operating state of the switch element 1508. In the comparative example, the control circuit 27 controls the switch element 1508 so that the switch element 1508 is closed at timing t8 and is open at timing t9.

[0065] As shown in FIG. 6, the control circuit 27 controls each switch element by switching between an open state and a closed state so that one switch element is always in a closed state.

[0066] (Control method of the embodiment) A method for controlling the transmission circuit 28 according to the embodiment will be described with reference to Fig. 7. Fig. 7 is a diagram for explaining a method for controlling the transmission circuit 28 according to the embodiment.

[0067] Fig. 7 shows the operating state of each switch element included in the transmission circuit 28. Fig. 7 shows waveforms W11, W12, W13, W14, W15, W16, W17, and W18 of the control signals of each switch element.

[0068] A waveform W11 indicates the operating state of the switch element 1501. In the embodiment, the control circuit 27 controls the switch element 1501 so that the switch element 1501 is in a closed state at a timing t11 and in an open state at a timing t12.

[0069] A waveform W12 indicates the operating state of the switch element 1502. In the embodiment, the control circuit 27 controls the switch element 1502 so that the switch element 1502 is in a closed state at a timing t12 and in an open state at a timing t13.

[0070] A waveform W13 indicates the operating state of the switch element 1503. In the embodiment, the control circuit 27 controls the switch element 1503 so that the switch element 1503 is in a closed state at a timing t13 and in an open state at a timing t14.

[0071] A waveform W14 indicates the operating state of the switch element 1504. In the embodiment, the control circuit 27 controls the switch element 1504 so that the switch element 1504 is in a closed state at a timing t14 and in an open state at a timing t15.

[0072] A waveform W15 indicates the operating state of the switch element 1505. In the embodiment, the control circuit 27 controls the switch element 1505 so that the switch element 1505 is in a closed state at a timing t15 and in an open state at a timing t16.

[0073] A waveform W16 indicates the operating state of the switch element 1506. In the embodiment, the control circuit 27 controls the switch element 1506 to be in a closed state at a timing t16 and in an open state at a timing t17.

[0074] A waveform W17 shows the operating state of the switch element 1507. As shown in the waveform W17, in the embodiment, the switch element 1507 is always in an open state. That is, in the embodiment, the control circuit 27 does not close the switch element 1507. That is, in the embodiment, the capacitor C7 connected to the switch element 1507 is not added to the transmission circuit 28. In other words, in the embodiment, the control circuit 27 is configured to control each switch element so that not all the capacitors included in the transmission circuit 28 are used, but at least one of all the capacitors is not used. For example, the control circuit 27 selects the switch elements 150 that are not controlled so that the change in impedance on the complex plane caused by controlling each switch element is at equal intervals.

[0075] A waveform W18 indicates the operating state of the switch element 1508. In the embodiment, the control circuit 27 controls the switch element 1508 so that it is in a closed state at timing t17 and in an open state at timing t18.

[0076] 7, after the switch element 1508 is opened at timing t18, there is a period during which all switch elements are in the open state until the switch element 1501 is closed at timing t19. In the embodiment, by providing a period during which all switch elements are in the open state, the radius of the circle used for rotationally controlling the impedance is changed on the complex plane. In other words, the embodiment is configured to be able to control the impedance to rotate on a distorted circle compared to a perfect circle on the complex plane by providing a period during which all switch elements are in the open state.

[0077] For example, when the radius of the circle of the reflection coefficient of the output terminal on the antenna side when all of the multiple switch elements are used (comparative example) is X, in the embodiment, the control circuit 27 is configured to control the multiple switch elements so that the radius of the circle of the reflection coefficient is not less than X and not more than X+0.2.

[0078] A method for performing rotation control of the impedance of an output terminal on the antenna side of a transmission circuit according to an embodiment will be described with reference to Fig. 8. Fig. 8 is a diagram for explaining a method for performing rotation control of the impedance of an output terminal on the antenna side of a transmission circuit according to an embodiment.

[0079] Fig. 8 shows a change in impedance as viewed from the output terminal on the antenna side in Fig. 5 in a Smith chart. Graph 201 shows the change in impedance according to the embodiment. Graph 202 shows the change in impedance according to the comparative example.

[0080] As shown in graph 202, in the comparative example, the impedance changes so as to rotate on a circle in the Smith chart. As shown in graph 201, in the embodiment, the impedance changes so as to rotate on a distorted circle compared to the comparative example. In graph 201, points P1 and P2 that are off the circular orbit indicate the impedance when all switch elements in transmission circuit 28 are in an open state.

[0081] [Backscatter signal] An example of a backscattering signal according to a comparative example and an embodiment will be described with reference to Fig. 9 and Fig. 10. Fig. 9 is a diagram showing an example of a spectrum waveform of a backscattering signal according to a comparative example. Fig. 10 is a diagram showing an example of a spectrum waveform of a backscattering signal according to an embodiment. In Fig. 9 and Fig. 10, the horizontal axis indicates frequency [MHz (megahertz)], and the vertical axis indicates signal level [dBm (decibels milliwatts)].

[0082] FIG. 9 shows a spectrum waveform W21 according to a comparative example. The spectrum waveform W21 includes a carrier signal RF1, a USB signal US1, an LSB signal LS1, a third harmonic signal TH1, and a third harmonic signal TH2. The frequency of the carrier signal RF1 is 918 [MHz]. The frequency of the LSB signal LS1 is 917.8 [MHz]. The frequency of the USB signal US1 is 918.2 [MHz]. As shown in FIG. 9, the LSB signal LS1 is suppressed compared to the USB signal US1. The difference between the USB signal US1 and the LSB signal LS1 is about 19 [dB (decibels)]. The line L1 is a line showing a signal level of -20 [dB] with respect to the USB signal US1. The third harmonic signal TH1 and the third harmonic signal TH2 are below -20 [dB].

[0083] FIG. 10 shows a spectrum waveform W22 according to the embodiment. The spectrum waveform W22 includes a carrier signal RF2, a USB signal US2, an LSB signal LS2, a third harmonic signal TH3, and a third harmonic signal TH4. The frequency of the carrier signal RF2 is 918 [MHz]. The frequency of the LSB signal LS2 is 917.8 [MHz]. The frequency of the USB signal US2 is 918.2 [MHz]. As shown in FIG. 10, the LSB signal LS2 is suppressed compared to the USB signal US2. The difference between the USB signal US2 and the LSB signal LS2 is about 36 [dB (decibels)]. The line L2 is a line showing a signal level of -20 [dB] for the USB signal US2. The third harmonic signal TH3 and the third harmonic signal TH4 are less than -20 [dB]. That is, in the embodiment, the difference between the USB signal US2 and the LSB signal LS2 is larger than the difference between the USB signal US1 and the LSB signal LS1 shown in FIG. 9, and therefore the characteristics are improved.

[0084] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the contents of these embodiments. The above-mentioned components include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-mentioned components can be appropriately combined. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the gist of the above-mentioned embodiments. [Explanation of symbols]

[0085] 1. Wireless communication devices 10 Antennas 11 BPF 20 RFBS Devices 21 High Frequency Switch 22 Amplifier 23 Demodulation section 24 Oscillator 25,26 LPF 27 Control circuit 28 Transmission Circuit 30 Control device 40 Sensors 120 Capacitor Circuit 140 Signal source 150 Switching element 160 Capacitor IC 170 Phase shifter 190 Changeover switch element 200 Changeover switch control circuit

Claims

1. A transmission circuit configured to be connected to an antenna, The transmission circuit includes: A plurality of impedance circuits each having a different impedance; a plurality of switch elements, any one of which is connected to each of the plurality of impedance circuits; A control circuit configured to control opening and closing of the plurality of switch elements, The control circuit is configured to selectively change the opening and closing of the multiple switch elements to control the reflection coefficient of the output terminal on the antenna side to rotate on a distorted circle compared to a perfect circle in a complex plane.

2. 2. The transmission circuit according to claim 1, The control circuit is configured to control a reflection coefficient of the output terminal on the antenna side by not using at least one of the plurality of switch elements.

3. 3. The transmission circuit according to claim 1, the control circuit is configured to control the plurality of switch elements so that, when a radius of a circle of a reflection coefficient of the output terminal on the antenna side when all of the plurality of switch elements are used is X, the radius of the circle of the reflection coefficient is equal to or greater than X and equal to or less than X+0.

2.

4. 3. The transmission circuit according to claim 1, The transmission circuit, wherein the control circuit is configured to control the plurality of switch elements so as to provide a period during which all of the plurality of switch elements are in an open state.

5. 3. The transmission circuit according to claim 1, A transmission circuit, wherein the plurality of impedance circuits include a plurality of capacitor circuits configured to adjust a capacitance among reactance components of impedance.

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