10 side.

The inductor circuit 110₁includes a signal source 140₁, a switch element 150₁, and an inductor L1. A signal source 140₁indicates a signal source to which a control signal from the control circuit 27 is supplied. The signal source 140₁is configured to output the control signal to the switch element 150₁to control an opening/closing operation of the switch element 150₁. The switch element 150₁includes one input terminal to which the signal source 140₁is connected and the other input terminal to which a reference potential is connected. The reference potential is described as being the ground, but the present disclosure is not limited thereto. The switch element 150₁is configured to switch between a closed state and an open state in accordance with the control signal from the signal source 140₁.

The switch element 150₁includes one end to which the signal line 101 is electrically connected and the other end to which one end of the inductor L1 is electrically connected. The other end of the inductor L1 is connected to the reference potential. In this case, the switch element 150₁is configured to electrically connect the signal line 101 and the inductor L1 by being in the closed state. The switch element 150₁is configured to electrically separate the signal line 101 from the inductor L1 by being in the open state. The inductance of the inductor L1 is added to the impedance of the transmission circuit 28 by electrically connecting the signal line 101 and the inductor L1. In other words, a reactance component of the impedance of the transmission circuit 28 changes due to addition of the inductance of the inductor L1. The inductance of the inductor L1 is, for example, 3.3 [nano Henry (nH)].

The inductor circuit 110₂includes a signal source 140₂, a switch element 150₂, and an inductor L2. A signal source 140₂indicates a signal source to which a control signal from the control circuit 27 is supplied. The signal source 140₂is configured to output the control signal to the switch element 150₂to control an opening/closing operation of the switch element 150₂. The switch element 150₂includes one input terminal to which the signal source 140₂is connected and the other input terminal to which the reference potential is connected. The reference potential is described as being a ground, but the present disclosure is not limited thereto. The switch element 150₂is configured to switch between the closed state and the open state in accordance with the control signal from the signal source 140₂.

The switch element 150₂includes one end to which the signal line 101 is electrically connected and the other end to which one end of the inductor L2 is electrically connected. The other end of the inductor L2 is connected to the reference potential. In this case, the switch element 150₂is configured to electrically connect the signal line 101 and the inductor L2 by being in the closed state. The switch element 150₂is configured to electrically separate the signal line 101 from the inductor L2 by being in the open state. The inductance of the inductor L2 is added to the impedance of the transmission circuit 28 by electrically connecting the signal line 101 and the inductor L2. In other words, a reactance component of the impedance of the transmission circuit 28 changes due to addition of the inductance of the inductor L2. The inductance of the inductor L2 is, for example, 7.96 [nH].

The inductor circuit 110₃includes a signal source 140₃, a switch element 150₃, and an inductor L3. The signal source 140₃indicates a signal source to which the control signal from the control circuit 27 is supplied. The signal source 140₃is configured to output the control signal to the switch element 150₃to control an opening/closing operation of the switch element 150₃. The switch element 150₃includes one input terminal to which the signal source 140₃is connected and the other input terminal to which the reference potential is connected. The reference potential is described as being the ground, but the present disclosure is not limited thereto. The switch element 150₃is configured to switch between the closed state and the open state in accordance with the control signal from the signal source 140₃. Note that one or more inductor circuits among the inductor circuits 110₁to 110₃may include one or more electrical elements from a plurality of capacitor elements and a plurality of resistive elements.

The switch element 150₃includes one end to which the signal line 101 is electrically connected and the other end to which one end of the inductor L3 is electrically connected. The other end of the inductor L3 is connected to the reference potential. In this case, the switch element 150₃is configured to electrically connect the signal line 101 and the inductor L3 by being in the closed state. The switch element 150₃is configured to electrically separate the signal line 101 from the inductor L3 by being in the open state. The inductance of the inductor L3 is added to the impedance of the transmission circuit 28 by electrically connecting the signal line 101 and the inductor L3. In other words, a reactance component of the impedance of the transmission circuit 28 changes due to addition of the inductance of the inductor L3. The inductance of the inductor L3 is, for example, 19.21 [nH].

The capacitor circuit 120₁includes a signal source 140₄, a switch element 150₄, and a capacitor C1. The signal source 140₄indicates a signal source to which the control signal from the control circuit 27 is supplied. The signal source 140₄is configured to output the control signal to the switch element 150₄to control an opening/closing operation of the switch element 150₄. The switch element 150₄includes one input terminal to which the signal source 140₄is connected and the other input terminal to which the reference potential is connected. The reference potential is described as being the ground, but the present disclosure is not limited thereto. The switch element 150₄is configured to switch between the closed state and the open state in accordance with the control signal from the signal source 140₄.

The switch element 150₄includes one end to which the signal line 101 is electrically connected and the other end to which one end of the capacitor C1 is electrically connected. The other end of the capacitor C1 is connected to the reference potential. In this case, the switch element 150₄is configured to electrically connect the signal line 101 and the capacitor C1 by being in the closed state. The switch element 150₄is configured to electrically separate the signal line 101 from the capacitor C1 by being in the open state. The capacitance of the capacitor C1 is added to the impedance of the transmission circuit 28 by electrically connecting the signal line 101 and the capacitor C1. In other words, a reactance component of the impedance of the transmission circuit 28 changes due to addition of the capacitance of the capacitor C1. The capacitance of the capacitor C1 is, for example, 1.32 [pico Farad (pF)].

The capacitor circuit 120₂includes a signal source 140₅, a switch element 150₅, and a capacitor C2. The signal source 140₅indicates a signal source to which the control signal from the control circuit 27 is supplied. The signal source 140₅is configured to output the control signal to the switch element 150₅to control an opening/closing operation of the switch element 150₅. The switch element 150₅includes one input terminal to which the signal source 140₅is connected and the other input terminal to which the reference potential is connected. The reference potential is described as being the ground, but the present disclosure is not limited thereto. The switch element 150₅is configured to switch between the closed state and the open state in accordance with the control signal from the signal source 140₅.

The switch element 150₅includes one end to which the signal line 101 is electrically connected and the other end to which one end of the capacitor C2 is electrically connected. The other end of the capacitor C2 is connected to the reference potential. In this case, the switch element 150₅is configured to electrically connect the signal line 101 and the capacitor C2 by being in the closed state. The switch element 150₅is configured to electrically separate the signal line 101 from the capacitor C2 by being in the open state. The capacitance of the capacitor C2 is added to the impedance of the transmission circuit 28 by electrically connecting the signal line 101 and the capacitor C2. In other words, a reactance component of the impedance of the transmission circuit 28 changes due to addition of the capacitance of the capacitor C2. The capacitance of the capacitor C2 is, for example, 3.18 [pF].

The capacitor circuit 120₃includes a signal source 140₆, a switch element 150₆, and a capacitor C3. The signal source 140₆indicates a signal source to which the control signal from the control circuit 27 is supplied. The signal source 140₆is configured to output the control signal to the switch element 150₆to control an opening/closing operation of the switch element 150₆. The switch element 150₆includes one input terminal to which the signal source 140₆is connected and the other input terminal to which the reference potential is connected. The reference potential is described as being the ground, but the present disclosure is not limited thereto. The switch element 150₆is configured to switch between the closed state and the open state in accordance with the control signal from the signal source 140₆. Note that one or more capacitor circuits among the capacitor circuits 120₁to 120₃may include one or more electrical elements among a plurality of inductor elements and the plurality of resistive elements.

The switch element 150₆includes one end to which the signal line 101 is electrically connected and the other end to which one end of the capacitor C3 is electrically connected. The other end of the capacitor C3 is connected to the reference potential. In this case, the switch element 150₆is configured to electrically connect the signal line 101 and the capacitor C3 by being in the closed state. The switch element 150₆is configured to electrically separate the signal line 101 from the capacitor C3 by being in the open state. The capacitance of the capacitor C3 is added to the impedance of the transmission circuit 28 by electrically connecting the signal line 101 and the capacitor C3. In other words, a reactance component of the impedance of the transmission circuit 28 changes due to addition of the capacitance of the capacitor C3. The capacitance of the capacitor C3 is, for example, 7.68 [pF].

The resistive circuit 130 includes a signal source 140₇, a switch element 150₇, and a resistive element R1. The signal source 140₇indicates a signal source to which the control signal from the control circuit 27 is supplied. The signal source 140₇is configured to output the control signal to the switch element 150₇to control an opening/closing operation of the switch element 150₇. The switch element 150₇includes one input terminal to which the signal source 140₇is connected and the other input terminal to which the reference potential is connected. The reference potential is described as being the ground, but the present disclosure is not limited thereto. The switch element 150₇is configured to switch between the closed state and the open state in accordance with the control signal from the signal source 140₇.

The switch element 150₇includes one end to which the signal line 101 is electrically connected and the other end to which one end of the resistive element R1 is electrically connected. The other end of the resistive element R1 is connected to the reference potential. In this case, the switch element 150₇is configured to electrically connect the signal line 101 and the resistive element R1 by being in the closed state. The switch element 150₇is configured to electrically separate the signal line 101 from the resistive element R1 by being in the open state. A resistance value of the resistive element R1 is added to the impedance of the transmission circuit 28 by electrically connecting the signal line 101 and the resistive element R1. In other words, the impedance of the transmission circuit 28 changes in the real component by the resistance value of the resistive element R1 being added. The resistance value of the resistive element R1 is, for example, 1 [milli-Ohm (mΩ)].

The control circuit 27 is configured to selectively change the impedance of the transmission circuit 28 to control the reflection coefficient to rotate on the polar chart by selectively controlling open/closed state of each of the switch elements 150₁to 150₇. The control circuit 27 is configured to control the impedance of the transmission circuit 28 to rotate in the complex plane by causing any one of the switch elements 150₁to 150₇to be in the closed state or by causing all of the switch elements to be in the open state. Alternatively, the control circuit 27 may control the reflection coefficient to rotate by selecting the impedance of the transmission circuit 28 by causing the plurality of switch elements among the switch elements 150₁to 150₇to be in the closed state.

Specifically, the transmission circuit 28 is configured such that, when all of the switch elements 150₁to 150₇are in the open state, the reflection coefficient is located at 0° in the complex plane. The transmission circuit 28 is configured such that, when only the switch element 150₃is in the closed state, the impedance is located at 45° in the complex plane. The transmission circuit 28 is configured such that, when only the switch element 150₂is in the closed state, the impedance is located at 90° in the complex plane. The transmission circuit 28 is configured such that, when only the switch element 150₁is in the closed state, the impedance is located at 135° in the complex plane. The transmission circuit 28 is configured such that, when only the switch element 150₄is in the closed state, the impedance is located at −45° in the complex plane. The transmission circuit 28 is configured such that, when only the switch element 150₅is in the closed state, the impedance is located at −90° in the complex plane. The transmission circuit 28 is configured such that, when only the switch element 150₆is in the closed state, the impedance is located at −135° in the complex plane. The transmission circuit 28 is configured such that, when only the switch element 150₇is in the closed state, the impedance is located at 180° in the complex plane.

The control circuit 27 may be configured to control the open/closed state of a predetermined switch element(s) among the switch elements 150₁to 150₇when reflecting the transmitted radio wave. The control circuit 27 may be configured to control the switch elements 150₁to 150₇such that the impedance is located at a rotational position in the complex plane, in accordance with output from the sensor 40. The control circuit 27 may be configured to control the switch elements 150₁to 150₇such that the impedance is located at the rotational position in the complex plane, based on the control signal transmitted from the outside of the wireless communication apparatus 1.

A method of implementing the single side band pertaining to the transmission circuit 28 will be described with reference to FIG. 5.

FIG. 5 illustrates a result example of analyzing the frequency spectrum of the backscatter signal when the reflection coefficient is rotated counterclockwise. A spectrum waveform of the backscatter signal (reflection signal) transmitted by the wireless communication apparatus 1 is illustrated. The horizontal axis represents frequency, and the vertical axis represents signal intensity. In FIG. 5, a carrier signal 61, a USB signal 62, and an LSB signal 63 are illustrated. The frequency of the carrier signal 61 is, for example, 1.0 [Giga Hertz (GHz)]. The frequency of the USB signal 62 is, for example, 1.001 [GHz]. The frequency of the LSB signal 63 is, for example, 0.999 [GHz]. The spectrum intensity of the carrier signal 61 illustrated in FIG. 5 is approximately −48 [Decibel (dB)]. The spectrum intensity of the USB signal 62 is approximately 0 [dB]. The spectrum intensity of the LSB signal 63 is approximately −60 [dB]. The difference in spectrum intensity between the USB signal 62 and the LSB signal 63 is −60 [dB]. In other words, in the spectrum waveform illustrated in FIG. 5, the LSB signal 63 is suppressed as compared with the USB signal 62, and thus the single side band of the USB signal 62 is implemented.

As described above, the transmission circuit 28 can implement the single side band by selectively changing the impedance of the transmission circuit 28 to control the reflection coefficient to rotate. In other words, the transmission circuit 28 can independently utilize both side bands, and improvement of the utilization efficiency of the frequency band can be doubled by controlling the impedance of the transmission circuit 28 so as to suppress either the LSB signal or the USB signal with respect to the carrier signal.

The transmission circuit 28 can implement the single side band of the backscatter signal without using a configuration such as a demultiplexer. Thus, the transmission circuit 28 does not require the configuration such as the demultiplexer, and thus the wireless communication apparatus of the backscatter system can be miniaturized.

Note that the transmission circuit 28 is described as controlling the impedance at eight points in the 450 increments of 0°, 45°, 90°, 135°, 180°, −135°, −90°, and −45° in the complex plane. These angles are exemplary and are not intended to limit the present disclosure. The number of points at which the impedance is rotationally controlled is not particularly limited, and may be three, four, six, ten or more. The number of points at which the impedance is rotationally controlled is preferably four or more. The number of points at which the impedance is rotationally controlled is preferably a multiple of four. In the points at which the impedance is rotationally controlled, angular intervals between points may be the same or different from each other. In the first embodiment, the angular intervals of the points for rotationally controlling the impedance includes not only a case where they exactly match with one another but also a case where they are sifted by a predetermined angle (for example, within 10°). In the first embodiment, an angle of a point serving as a reference for rotationally controlling the impedance may be shifted by any angle depending on a design. For example, if it is difficult to control the impedance of the point serving as the reference to 0°, the point may be shifted by about 20°.

Second Embodiment

Next, a transmission circuit according to a second embodiment of the present disclosure will be described. As described above, the transmission circuit 28 according to the first embodiment includes the inductor circuit 110, the capacitor circuit 120, and the resistive circuit 130 as the impedance circuit. However, the configuration of the transmission circuit of the present disclosure is not limited thereto. For example, the transmission circuit may be configured from the capacitor circuit 120 without including the inductor circuit 110 and the resistive circuit 130. In this case, the single side band can be implemented using the transmission circuit, a phase shifter that shifts a phase of the signal connected to the transmission circuit by 90°, and the switch element.

A configuration of the transmission circuit according to the second embodiment will be described with reference to FIG. 6. FIG. 6 is a diagram for describing an example of a configuration of the transmission circuit according to the second embodiment.

As illustrated in FIG. 6, the transmission circuit 28A includes the capacitor circuits 120₁to 120₃. The capacitor circuit 120₁includes the signal source 140₁and a switch element 150A₁; the capacitor circuit 120₂includes the signal source 140₂and a switch element 150A₂; the capacitor circuit 120₃includes the signal source 140₃and a switch element 150A₃. When it is not necessary to particularly distinguish the switch elements 150A₁to 150A₃from one another, they may be collectively referred to as a switch element 150A. The switch element 150A is similar to the switch element 150 described in the first embodiment, and thus description thereof is omitted.

Capacitor circuits 120₁to 120₃are electrically connected to one another by a signal line 103. The signal line 103 is electrically connected to an input/output terminal 104. The capacitor circuits 120₁to 120₃are circuits used in rotationally controlling the reflection coefficient clockwise or counterclockwise from −135° to −90° and from −90° to 0° in the complex plane (polar chart).

The capacitor circuits 120₁to 120₃are similar to the capacitor circuits 120₁to 120₃, respectively, described in the first embodiment. Specifically, capacitance of the capacitor C1 is 1.32 [pF]. The capacitance of the capacitor C2 is 3.18 [pF]. The capacitance of the capacitor C3 is 7.68 [pF].

The control circuit 27 can control the impedance of the transmission circuit 28A to rotate in the complex plane by controlling the open/closed state of each of the switch elements 150A₁to 150A₃. The control circuit 27 is controllable to rotate the impedance of the transmission circuit 28A in the complex plane by causing any one of the switch elements 150A₁to 150A₃to be in the closed state or by causing all of the switch elements to be in the open state. The control circuit 27 may be controllable to rotate the impedance of the transmission circuit 28A in the complex plane by causing the plurality of switch elements among the switch elements 150A₁to 150A₃to be in the open state.

When all of the switch elements 150A₁to 150A₃are in the open state, the transmission circuit 28A is configured such that the impedance is located at 0° in the complex plane. When only the switch element 150A₁is in the closed state, the transmission circuit 28A is configured such that the impedance is located at −45°. When only the switch element 150A₂is in the closed state, the transmission circuit 28A is configured such that the impedance is located at −90°. When only the switch element 150A₃is in the closed state, the transmission circuit 28A is configured such that the impedance is located at −135°. In other words, the control circuit 27 may control the position of the impedance on the complex plane with four-point switching by controlling the switch elements 150A₁to 150A₃. The capacitor circuits 120₁to 120₃may be configured to rotationally control the impedance between −135° and −90° and between −90° and 0°. The control circuit 27 is configured to rotationally control the impedance of the transmission circuit 28A clockwise by sequentially causing only one of the switch elements 150A₁, 150A₂, and 150A₃to be in the closed state. The control circuit 27 is configured to rotationally control the impedance of the transmission circuit 28A counterclockwise by sequentially causing only one of the switch elements 150A₃, 150A₂, and 150A₁to be in the closed state.

A method of rotationally controlling the impedance in the complex plane in the transmission circuit according to the second embodiment will be described with reference to FIG. 7. FIG. 7 is a diagram for describing a method of rotationally controlling the reflection coefficient in the complex plane according to the second embodiment (FIG. 6).

As illustrated in FIG. 7, the transmission circuit 28A (the capacitor circuits 120₁to 120₃) illustrated in FIG. 6 may be integrated and used as a capacitor IC 160. In this case, the capacitor IC 160 is configured to be connected to either a phase shifter 170 or a signal line 180 by switching of a changeover switch element 190 by a changeover switch control circuit 200.

The phase shifter 170 includes a capacitor, an inductor, and a capacitor, which are not illustrated. The phase shifter 170 shifts a phase of the input signal by 90° to output the shifted signal.

The changeover switch control circuit 200 controls the changeover switch element 190 to connect the capacitor IC 160 and the signal line 180 when rotationally controlling the impedance between 0° and −90° and between −90° and −135°.

The changeover switch control circuit 200 controls the changeover switch element 190 to connect the capacitor IC 160 and the phase shifter 170 when rotationally controlling the impedance between 45° and 90° and between 90° and 180°. The position of the impedance on the complex plane can be controlled with eight-point switching by connecting the capacitor IC 160 and the phase shifter 170. By forming an integrated circuit in this manner, a configuration advantageous for miniaturization can be obtained.

A method of implementing the single side band according to the second embodiment will be described with reference to FIG. 8.

FIG. 8 illustrates an analysis result of the frequency spectrum of the backscatter signal when the reflection coefficient is rotated counterclockwise. A spectrum waveform of the backscatter signal transmitted by the wireless communication apparatus 1 is illustrated. In FIG. 8, a carrier signal 61A, a USB signal 62A, and an LSB signal 63A are illustrated. The frequency of the carrier signal 61A is, for example, 1.0 [GHz]. The frequency of the USB signal 62A is 1.001 [GHz]. The frequency of the LSB signal 63A is 0.999 [GHz]. The spectrum intensity of the carrier signal 61A is approximately −50 [dB]. The spectrum intensity of the USB signal 62A is approximately 0 [dB]. The spectrum intensity of the LSB signal 63A is approximately −50 [dB]. The difference in spectrum intensity between the USB signal 62A and the LSB signal 63A is approximately −50 [dB]. In other words, in the spectrum waveform illustrated in FIG. 8, the LSB signal 63 is suppressed as compared with the USB signal 62, and thus the single side band of the USB signal 62 is implemented.

In the second embodiment illustrated in FIG. 7, the use of the inductor having larger size than the resistive element and the capacitor can be reduced. In the second embodiment shown in FIG. 7, since it is easy to form an IC, the configuration is more advantageous for miniaturization.