Wireless communication device

Abstract

To provide a wireless communication device that can perform carrier sensing even when leakage occurs in the modulator. [Solution] The wireless communication device according to the embodiment comprises a first filter, an oscillator circuit, a modulation circuit, and a demodulator. The first filter restricts the input signal to a first passband. The oscillator circuit outputs a first signal with a frequency outside the first passband. The modulation circuit modulates the first signal to a second signal that detunes a predetermined frequency from the frequency at which the received signal strength is measured. The demodulator demodulates the signal that has passed through the first filter based on the second signal.

Description

Technical Field

[0001] Embodiments of the present invention relate to a wireless communication device.

Background Art

[0002] A direct conversion radio capable of carrier sense even when receiving an unmodulated wave is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When leakage occurs in the modulator, signals of multiple frequencies are input to the demodulator, beats occur in the output of the demodulator, and carrier sense may become difficult. An embodiment of the present invention provides a wireless communication device capable of carrier sense even when leakage occurs in the modulator.

Means for Solving the Problems

[0005] The wireless communication device according to the embodiment includes a first filter, an oscillation circuit, a modulation circuit, and a demodulator. The first filter limits the input signal to a first passband. The oscillation circuit outputs a first signal having a frequency outside the first passband. The modulation circuit modulates the first signal into a second signal that detunes a predetermined frequency from the frequency for measuring the received signal strength. The demodulator demodulates the signal that has passed through the first filter based on the second signal.

Brief Description of the Drawings

[0006] [Figure 1] A block diagram showing a configuration example of a wireless communication device according to the first embodiment. [Figure 2]A table showing an example of the characteristics of each part of the wireless communication device according to the first embodiment. [Figure 3] A table showing an example of the frequencies of each signal in the carrier sense operation of the wireless communication device according to the first embodiment. [Figure 4] A block diagram showing an example configuration of a wireless communication device according to the first embodiment. [Figure 5] A table showing an example of the frequencies of each signal in the communication operation of the wireless communication device according to the first embodiment. [Figure 6] A block diagram showing an example configuration of a wireless communication device according to the second embodiment. [Figure 7] A table showing an example of the characteristics of each part of the wireless communication device according to the second embodiment. [Figure 8] A table showing an example of the frequencies of each signal in the carrier sense operation of the wireless communication device according to the second embodiment. [Figure 9] A block diagram showing an example configuration of a wireless communication device according to the second embodiment. [Figure 10] A table showing an example of the frequencies of each signal in the communication operation of the wireless communication device according to the second embodiment. [Modes for carrying out the invention]

[0007] The embodiments will be described below with reference to the drawings. In the description, components having substantially the same function and configuration will be denoted by the same reference numerals. Furthermore, the embodiments shown below are illustrative of the technical concept. The embodiments do not specify the material, shape, structure, arrangement, etc., of the components. Various modifications can be made to the embodiments.

[0008] <First Embodiment> <Structure> Figure 1 is a block diagram showing an example configuration of a wireless communication device according to the first embodiment. The wireless communication device 1 is a wireless tag reader / writer that communicates with a wireless tag and reads information stored in the wireless tag and writes information to the wireless tag. The wireless tag is typically an RFID (Radio Frequency Identification) tag. The wireless communication device 1 includes a CPU (Central Processing Unit) 100, a local oscillator 101, a quadrature modulator 102, a DA (Digital to Analog) converter 103, a distributor 104, a switch 105, a first BPF (Band Pass Filter) 106, a power amplifier 107, an LPF (Low Pass Filter) 108, an antenna 109, an antenna sharer 110, a second BPF 111, a low-noise amplifier 112, a quadrature demodulator 113, a third BPF 114, an amplifier 115, and an AD (Analog to Digital) converter 116.

[0009] The CPU 100 controls the overall operation of the wireless communication device 1.

[0010] The local oscillator 101 is an oscillation circuit that generates a signal by oscillating at a frequency based on the control of the CPU 100, and outputs the generated signal to the quadrature modulator 102 and the switch 105.

[0011] The quadrature modulator 102 is a modulation circuit that modulates the output of the local oscillator 101 based on the output of the DA converter 103 and outputs it to the distributor 104.

[0012] The DA converter 103 is a circuit that converts the digital signal input from the CPU 100 into an analog signal and outputs it to the quadrature modulator 102.

[0013] The distributor 104 is a circuit that distributes the output of the quadrature modulator 102 to the switch 105 and the first BPF 106, respectively, and outputs them.

[0014] Based on the control of the CPU 100, the switch 105 is a circuit that outputs either the signal input from the local oscillator 101 or the signal input from the distributor 104 to the quadrature demodulator 113. In this specification, the state in which the switch 105 outputs the signal input from the distributor 104 to the quadrature demodulator 113 is referred to as the first state. The state in which the switch 105 outputs the signal input from the local oscillator 101 to the quadrature demodulator 113 is referred to as the second state. In the example shown in FIG. 1, the switch 105 is in the first state.

[0015] The first BPF 106 is a circuit that restricts the signal input from the distributor 104 to the first frequency band and outputs it to the power amplifier 107. The first frequency band includes at least the frequency band of the radio wave that the wireless communication device Ⅰ transmits from the antenna 109 to the outside.

[0016] The power amplifier 107 is a circuit that power-amplifies the signal input from the first BPF 106 and outputs it to the LPF 108. The power amplifier 107 switches between an on state in which the input signal is power-amplified and output and an off state in which no signal is output based on the control of the CPU 100.

[0017] The LPF 108 is a circuit that passes the components of the signal input from the power amplifier 107 having frequencies lower than the cut-off frequency and outputs them to the antenna duplexer 110. The cut-off frequency is higher than the frequency used when the wireless communication device Ⅰ communicates with the wireless tag and lower than twice the frequency used when the wireless communication device Ⅰ communicates with the wireless tag.

[0018] The antenna 109 is an antenna that emits the supplied signal as a radio wave into space and receives the radio wave in space and outputs it as a signal. The antenna 109 is connected to the antenna duplexer 110.

[0019] The antenna sharer 110 is a circuit for switching between transmitting and receiving with antenna 109. The antenna sharer 110 supplies the signal input from LPF 108 to antenna 109 and outputs the signal received by antenna 109 to the second BPF 111.

[0020] The second BPF 111 is a circuit that restricts the signal input from the antenna sharer 110 to a second frequency band and outputs it to the low-noise amplifier 112. The second frequency band includes at least the frequency band of the signal used for communication between the wireless communication device 1 and the wireless tag.

[0021] The low-noise amplifier 112 is an amplification circuit that amplifies the signal input from the second BPF 111 and outputs it to the quadrature demodulator 113. The low-noise amplifier 112 has superior low-noise performance compared to other amplifiers included in the wireless communication device 1, such as the power amplifier 107 and amplifier 115.

[0022] The quadrature demodulator 113 is a circuit that demodulates the signal input from the low-noise amplifier 112 based on the signal input from the switch 105 and outputs it to the third bandpass filter 114.

[0023] The third BPF 114 is a circuit that limits the signal input from the quadrature demodulator 113 to a third frequency band and outputs it to the amplifier 115. The third frequency band includes at least the frequency band of the signal that the radio tag superimposes on the carrier frequency and a predetermined frequency that is detuned from the frequency used in the carrier sense operation described later to measure the received signal strength. Furthermore, the third frequency band does not include the frequency difference between the frequency of the signal output by the local oscillator 101 and the frequency of the signal output by the quadrature modulator 102 in the carrier sense operation described later.

[0024] Amplifier 115 is an amplification circuit that amplifies the signal input from the third BPF 114 and outputs it to the AD converter 116.

[0025] The AD converter 116 is a circuit that converts the signal input from the amplifier 115 into a digital signal and outputs it to the CPU 100.

[0026] To simplify the following explanation, the frequencies of the signals input and output by each part of the wireless communication device 1 are given names. Let Fa be the frequency of the signal that the local oscillator 101 outputs to the quadrature modulator 102 and the switch 105, respectively. Let Fb be the frequency of the signal that the quadrature modulator 102 outputs. Let Fc be the frequency of the signal that the distributor 104 outputs to the switch 105 and the first BPF 106, respectively. Let Fd be the frequency of the signal that the switch 105 outputs. Let Fe be the frequency of the signal that the antenna sharer 110 outputs. Let Ff be the frequency of the signal that the second BPF 111 outputs. Let Fg be the frequency of the signal that the low-noise amplifier 112 outputs. Let Fh be the frequency of the signal that the quadrature demodulator 113 outputs. Let Fi be the frequency of the signal that the third BPF 114 outputs.

[0027] <Operation> The operation of the wireless communication device 1 will be explained using specific numerical values ​​as an example. In the example shown herein, the wireless communication device 1 and the wireless tag communicate using a carrier frequency of 916.8 MHz. The frequency band of the signal that the wireless tag superimposes on the carrier frequency is, for example, 100 Hz to 30 kHz. The predetermined frequency used in the carrier sense operation described later, which is detuned from the frequency used to measure the received signal strength, is, for example, 30 kHz.

[0028] Figure 2 is a table showing an example of the characteristics of each part of the wireless communication device according to the first embodiment. As shown in Figure 2, the passband of the first BPF106 is 915MHz to 925MHz. The passband of the second BPF111 is 915MHz to 925MHz. The passband of the third BPF114 is 10Hz to 200kHz. The passband of the LPF108 is DC to 1.3GHz.

[0029] The carrier sense operation of the wireless communication device 1 will now be described. Carrier sense operation is the operation of measuring the received signal strength at the frequency to be measured. In the example described herein, the carrier sense operation is performed at the carrier frequency of 916.8 MHz. During the carrier sense operation, the CPU 100 controls the switch 105 to the first state and controls the power amplifier 107 to the off state. In other words, Figure 1 can be said to be a diagram showing the state of the wireless communication device 1 during the carrier sense operation.

[0030] Figure 3 is a table showing an example of the frequencies of each signal in the carrier sense operation of the wireless communication device according to the first embodiment. The carrier sense operation will be explained with reference to the frequencies of each signal shown in Figure 3.

[0031] In carrier sense operation, the local oscillator 101 outputs a signal at a frequency outside the passband of the second BPF 111. For example, the local oscillator 101 outputs a 910 MHz signal. That is, as shown in Figure 3, the frequency Fa is 910 MHz.

[0032] The quadrature modulator 102 modulates the signal input from the local oscillator 101 into a signal that detunes a predetermined frequency from the frequency at which the received signal strength is measured. Specifically, the quadrature modulator 102 modulates the 910MHz signal input from the local oscillator 101 from 916.8MHz, the frequency at which the received signal strength is measured, to 916.83MHz, which is a signal that detunes by a predetermined frequency of 30kHz. At this time, in addition to the modulated signal of 916.83MHz, the input signal of 910MHz is also leaked and output from the output of the quadrature modulator 102. Therefore, the frequencies Fb are 916.83MHz and 910MHz.

[0033] The distributor 104 distributes the input signal and outputs it without changing the frequency. Therefore, the frequencies Fc are the same as frequencies Fb, 916.83 MHz and 910 MHz.

[0034] Switch 105 is controlled to the first state by the CPU 100 during carrier sense operation. Therefore, switch 105 outputs the signal input from the distributor 104 to the quadrature demodulator 113. Since switch 105 does not change the frequency, the frequency Fd is the same as the frequency Fc, 916.83MHz and 910MHz.

[0035] The first BPF 106 band-limits the input signal and outputs it to the power amplifier 107. The power amplifier 107 is controlled to be in the off state by the CPU 100 during carrier sense operation and therefore does not output a signal. Consequently, no signal is input to the LPF 108, and the LPF 108 does not output a signal to the antenna sharer 110.

[0036] The antenna sharer 110 outputs the signals received by antenna 109. Here, we will explain using the example where antenna 109 receives signals at 916.8 MHz, 910.03 MHz, and 909.97 MHz. The frequencies Fe are 916.8 MHz, 910.03 MHz, and 909.97 MHz.

[0037] The second BPF 111 band-limits the input signal and outputs it to the low-noise amplifier 112. As explained with reference to Figure 2, the passband of the second BPF 111 is 915MHz to 925MHz, so 916.8MHz is passed through, and 910.03MHz and 909.97MHz are blocked. Therefore, the frequency Ff is 916.8MHz.

[0038] The low-noise amplifier 112 amplifies the input signal and outputs it without changing its frequency. Therefore, the frequency Fg is the same as the frequency Ff, at 916.8 MHz.

[0039] The quadrature demodulator 113 demodulates the signal with frequency Fg, i.e., the 916.8MHz signal, input from the low-noise amplifier 112, based on the signal with frequency Fd, i.e., the 916.83MHz and 910MHz signals input from the switch 105. The frequency Fh of the signal output by the quadrature demodulator 113 corresponds to the difference between these frequencies. Therefore, the frequency Fh is 30kHz, which is the difference between 916.83MHz and 916.8MHz; 6.8MHz, which is the difference between 916.8MHz and 910MHz; and 6.83MHz, which is the difference between 916.83MHz and 910MHz.

[0040] The third BPF 114 band-limits the input signal and outputs it to the amplifier 115. As explained with reference to Figure 2, the passband of the third BPF is 10Hz to 200kHz, so 30kHz is passed through, and 6.8MHz and 6.83MHz are blocked. Therefore, the frequency Fi is 30kHz.

[0041] The amplifier 115 amplifies the input signal and outputs it to the AD converter 116. The AD converter 116 converts the input signal into a digital signal and outputs it to the CPU 100. In this way, the CPU 100 detects the magnitude of a signal at a frequency of 30 kHz, that is, the magnitude of a signal at a predetermined frequency that is detuned from the frequency at which the received signal strength is measured. The wireless communication device 1 measures the received signal strength based on the magnitude of this signal.

[0042] Next, the communication operation of the wireless communication device 1 will be described. The communication operation involves sending and receiving information with the wireless tag. During the communication operation, the CPU 100 controls the switch 105 to the second state and controls the power amplifier 107 to the ON state.

[0043] Figure 4 is a block diagram showing an example configuration of a wireless communication device according to the first embodiment. Figure 4 shows the case where switch 105 is in the second state. In other words, Figure 4 can also be said to be a diagram showing the state of wireless communication device 1 during communication operation.

[0044] Figure 5 is a table showing an example of the frequencies of each signal in the communication operation of the wireless communication device according to the first embodiment. The communication operation will be explained with reference to the frequencies of each signal shown in Figure 5.

[0045] During communication, the local oscillator 101 outputs a signal at the carrier frequency used for communication. In the example shown herein, the carrier frequency is 916.8 MHz, so the local oscillator 101 outputs a signal at 916.8 MHz. That is, as shown in Figure 5, the frequency Fa is 916.8 MHz. Note that the carrier frequency is within the passband of the second BPF 111.

[0046] The quadrature modulator 102 outputs the signal input from the local oscillator 101 to the distributor 104 without frequency modulation. In communication operation, the quadrature modulator 102 may perform modulation other than frequency modulation, such as amplitude modulation. For example, the quadrature modulator 102 may include information to be transmitted to the wireless tag in the signal by amplitude modulation. Since the quadrature modulator 102 does not perform frequency modulation, the frequency Fb is the same as the frequency Fa, at 916.8 MHz.

[0047] The distributor 104 distributes the input signal and outputs it without changing the frequency. Therefore, the frequency Fc is the same as the frequency Fb, 916.8 MHz.

[0048] Switch 105 is controlled to the second state by the CPU 100 during communication operation. Therefore, switch 105 outputs the signal input from local oscillator 101 to quadrature demodulator 113. Since switch 105 does not change the frequency, frequency Fd is the same as frequency Fa, 916.8 MHz.

[0049] The first BPF 106 band-limits the input signal and outputs it to the power amplifier 107. As explained with reference to Figure 2, the passband of the first BPF 106 is 915MHz to 925MHz, so the 916.8MHz signal passes through the first BPF 106, is power-amplified by the power amplifier 107, and is output to the LPF 108. As explained with reference to Figure 2, the passband of the LPF 108 is DC to 1.3GHz, so the 916.8MHz signal passes through the LPF 108 and is output to the antenna sharer 110.

[0050] The antenna sharer 110 outputs the signal input from the LPF 108 to the antenna 109, and outputs the signal received by the antenna 109 to the second BPF 111. Here, we will explain using the example where the antenna 109 receives a 916.8MHz signal with a tag response superimposed, a 910.03MHz signal, and a 909.97MHz signal. The frequencies Fe are 916.8MHz (with tag response superimposed), 910.03MHz, and 909.97MHz.

[0051] The second BPF111 band-limits the input signal and outputs it to the low-noise amplifier 112. As explained with reference to Figure 2, the passband of the second BPF111 is 915MHz to 925MHz, so 916.8MHz (superimposed tag response) is passed through, while 910.03MHz and 909.97MHz are blocked. Therefore, the frequency Ff is 916.8MHz (superimposed tag response).

[0052] The low-noise amplifier 112 amplifies the input signal and outputs it without changing its frequency. Therefore, the frequency Fg is the same as the frequency Ff, 916.8 MHz (with tag response superimposed).

[0053] The quadrature demodulator 113 demodulates the signal with frequency Fg, i.e., the 916.8 MHz signal (superimposed tag response), input from the low-noise amplifier 112, based on the signal with frequency Fd, i.e., the 916.8 MHz signal input from the switch 105. The frequency Fh of the signal output by the quadrature demodulator 113 corresponds to the difference between these frequencies. Therefore, the frequency Fh is the tag response, which is the difference between 916.8 MHz and 916.8 MHz (superimposed tag response).

[0054] The third BPF 114 band-limits the input signal and outputs it to the amplifier 115. As explained with reference to Figure 2, the passband of the third BPF is 10Hz to 200kHz, so the tag response from 100Hz to 30kHz passes through. Therefore, the frequency Fi is the tag response.

[0055] The amplifier 115 amplifies the input signal and outputs it to the AD converter 116. The AD converter 116 converts the input signal into a digital signal and outputs it to the CPU 100. The CPU 100 acquires the tag response. In this way, the wireless communication device 1 communicates with the wireless tag.

[0056] When performing carrier sensing with a direct conversion radio, the demodulator demodulates the received signal based on a signal that detunes a predetermined frequency from the frequency at which the received signal strength is measured, and evaluates the predetermined frequency signal output from the demodulator. At this time, if a signal with a similar frequency is output along with the predetermined frequency signal, it becomes difficult to evaluate the predetermined frequency signal, and carrier sensing may not be possible.

[0057] The wireless communication device 1 according to the first embodiment includes a second BPF 111 that restricts the input signal to a first passband, a local oscillator 101 that outputs a first signal at a frequency outside the first passband, a quadrature modulator 102 that modulates the first signal to a second signal that detunes a predetermined frequency from the frequency at which the received signal strength is measured, and a quadrature demodulator 113 that demodulates the signal that has passed through the second BPF 111 based on the second signal. As a result, in the wireless communication device 1 according to the first embodiment, only the pair of the external signal to be confirmed in carrier sensing and the signal modulated by the quadrature modulator 102 will have a frequency difference of the predetermined frequency. In other words, by setting the output frequency of the local oscillator 101 outside the passband of the second BPF 111, the wireless communication device 1 according to the first embodiment can limit the external signals that generate a signal of a predetermined frequency at the output of the quadrature demodulator 113 to only the external signals to be confirmed in carrier sensing. Therefore, the wireless communication device 1 according to the first embodiment can perform carrier sensing even if leakage occurs in the modulator.

[0058] Furthermore, in the first embodiment of the wireless communication device 1, when measuring the received signal strength, the local oscillator 101 outputs a first signal, the quadrature modulator 102 outputs a second signal, and the quadrature demodulator 113 demodulates the signal that has passed through the second BPF 111 based on the second signal. When communicating with an external device, the local oscillator 101 outputs a third signal with a frequency within the first passband, and the quadrature demodulator 113 demodulates the signal that has passed through the second BPF 111 based on the third signal. In this way, when the wireless communication device 1 of the first embodiment communicates with an external device, i.e., a wireless tag, it handles frequencies within the passband of the second BPF 111, so it can communicate without any problems.

[0059] Furthermore, the wireless communication device 1 according to the first embodiment includes a second BPF 111, which is a bandpass filter circuit that limits the input signal to a first passband and outputs it. As a result, the wireless communication device 1 according to the first embodiment can limit the passband with the second BPF 111, thereby improving the degree of freedom in selecting the antenna 109.

[0060] Furthermore, the wireless communication device 1 according to the first embodiment further includes a third BPF 114 that limits the input signal to a second passband that does not include the frequency difference between the frequency of the first signal and the frequency of the second signal, and the output of the quadrature demodulator 113 is input to the third BPF 114. As a result, even if the quadrature demodulator 113 outputs a signal with the frequency difference between the frequency of the first signal and the frequency of the second signal, the wireless communication device 1 according to the first embodiment can remove it with the third BPF 114. Therefore, the wireless communication device 1 according to the first embodiment can perform carrier sensing even if leakage occurs in the modulator.

[0061] <Second Embodiment> A wireless communication device 1 according to the second embodiment will now be described. The wireless communication device 1 according to the second embodiment differs in some aspects of its configuration from the wireless communication device 1 according to the first embodiment. The differences between the wireless communication device 1 according to the second embodiment and the first embodiment will be described below.

[0062] <Structure> Figure 6 is a block diagram showing an example configuration of a wireless communication device according to the second embodiment. The wireless communication device 1 according to the second embodiment differs from the wireless communication device 1 according to the first embodiment in that the second BPF 111 is omitted and the antenna 109 is replaced with an antenna 117.

[0063] Antenna 117 is an antenna that emits a supplied signal as radio waves into space and receives radio waves from space and outputs them as signals. Antenna 117 functions as an antenna within the second frequency band, but does not function as an antenna outside the second frequency band.

[0064] Since the second BPF111 is omitted, the antenna sharer 110 outputs the signal received by antenna 117 to the low-noise amplifier 112.

[0065] To simplify the following explanation, the frequencies of the signals input and output by each part of the wireless communication device 1 are given names. The frequency of the signal output by the antenna sharer 110 and input to the low-noise amplifier 112 is denoted as Fj.

[0066] The other configurations of the wireless communication device 1 according to the second embodiment are the same as those of the wireless communication device 1 according to the first embodiment.

[0067] <Operation> The differences in the operation of the wireless communication device 1 according to the second embodiment compared to the first embodiment will be explained. An example of the signal frequency used to explain the operation of the wireless communication device 1 is the same as in the first embodiment.

[0068] Figure 7 is a table showing an example of the characteristics of each part of the wireless communication device according to the second embodiment. As shown in Figure 7, the passband of the antenna 117 is 915 MHz to 925 MHz. Other characteristics are the same as in the first embodiment.

[0069] The differences in the carrier sense operation of the wireless communication device 1 according to the second embodiment compared to the first embodiment will be explained. Figure 6 can also be described as a diagram showing the state of the wireless communication device 1 during carrier sense operation.

[0070] Figure 8 is a table showing an example of the frequencies of each signal in the carrier sense operation of the wireless communication device according to the second embodiment. The differences between the carrier sense operation and the first embodiment will be explained with reference to the frequencies of each signal shown in Figure 8.

[0071] The antenna sharer 110 outputs the signal received by antenna 117. Here, we will explain using the example where antenna 117 receives a signal at 916.8 MHz. As explained with reference to Figure 7, the passband of antenna 117 is 915 MHz to 925 MHz, so even if there are radio waves of 910.03 MHz or 909.97 MHz in space, antenna 117 will not receive them. Therefore, the frequency Fj is 916.8 MHz.

[0072] The low-noise amplifier 112 amplifies the input signal and outputs it without changing its frequency. Therefore, frequency Fg is the same as frequency Fj, at 916.8 MHz.

[0073] Other operations in the carrier sense operation are the same as in the first embodiment.

[0074] Next, the differences in the communication operation of the wireless communication device 1 according to the second embodiment compared to the first embodiment will be explained. Figure 9 is a block diagram showing an example configuration of the wireless communication device according to the second embodiment. Figure 9 shows the case where the switch 105 is in the second state. In other words, Figure 9 can also be said to be a diagram showing the state of the wireless communication device 1 in the communication state.

[0075] Figure 10 is a table showing an example of the frequencies of each signal in the communication operation of the wireless communication device according to the second embodiment. The differences in the communication operation from the first embodiment will be explained with reference to the frequencies of each signal shown in Figure 10.

[0076] The antenna sharer 110 outputs the signal input from the LPF 108 to the antenna 117, and outputs the signal received by the antenna 117 to the low-noise amplifier 112. Here, we will explain using the case where the antenna 117 receives 916.8 MHz with a superimposed tag response as an example. As explained with reference to Figure 7, the passband of the antenna 117 is 915 MHz to 925 MHz, so even if there are radio waves of 910.03 MHz or 909.97 MHz in space, the antenna 117 will not receive them. Therefore, the frequency Fj is 916.8 MHz (with superimposed tag response).

[0077] The low-noise amplifier 112 amplifies the input signal and outputs it without changing its frequency. Therefore, the frequency Fg is the same as the frequency Fj, 916.8 MHz (with tag response superimposed).

[0078] Other operations in the communication process are the same as in the first embodiment.

[0079] The wireless communication device 1 according to the second embodiment includes an antenna 117 that also functions as a filter to limit the input signal to a first passband, a local oscillator 101 that outputs a first signal with a frequency outside the first passband, a quadrature modulator 102 that modulates the first signal to a second signal that detunes a predetermined frequency from the frequency at which the received signal strength is measured, and a quadrature demodulator 113 that demodulates the signal that has passed through the antenna 117 based on the second signal. As a result, in the wireless communication device 1 according to the first embodiment, only the pair of the external signal to be confirmed in carrier sensing and the signal modulated by the quadrature modulator 102 will have a frequency difference of the predetermined frequency. In other words, the wireless communication device 1 according to the second embodiment can limit the external signals that generate a signal of a predetermined frequency at the output of the quadrature demodulator 113 to only the external signals to be confirmed in carrier sensing by setting the output frequency of the local oscillator 101 outside the passband of the antenna 117. Therefore, the wireless communication device 1 according to the second embodiment can perform carrier sensing even if leakage occurs in the modulator.

[0080] Furthermore, in the second embodiment of the wireless communication device 1, when measuring the received signal strength, the local oscillator 101 outputs a first signal, the quadrature modulator 102 outputs a second signal, and the quadrature demodulator 113 demodulates the signal that has passed through the antenna 117 based on the second signal. When communicating with an external device, the local oscillator 101 outputs a third signal with a frequency within the first passband, and the quadrature demodulator 113 demodulates the signal that has passed through the antenna 117 based on the third signal. In this way, when the wireless communication device 1 of the second embodiment communicates with an external device, i.e., a wireless tag, it handles frequencies within the passband of the antenna 117, so it can communicate without any problems.

[0081] Furthermore, the wireless communication device 1 according to the second embodiment achieves filter characteristics by an antenna 117 that functions within the first passband and does not function outside the first passband. As a result, the wireless communication device 1 according to the second embodiment can control the passband without configuring a bandpass filter with a circuit, thereby reducing the circuit size.

[0082] Furthermore, the wireless communication device 1 according to the second embodiment further includes a third BPF 114 that limits the input signal to a second passband that does not include the frequency difference between the frequency of the first signal and the frequency of the second signal, and the output of the quadrature demodulator 113 is input to the third BPF 114. As a result, even if the quadrature demodulator 113 outputs a signal with a frequency difference between the frequency of the first signal and the frequency of the second signal, the wireless communication device 1 according to the second embodiment can remove it with the third BPF 114. Therefore, the wireless communication device 1 according to the second embodiment can perform carrier sensing even if leakage occurs in the modulator.

[0083] <Other variations, etc.> In this specification, the functions of bandpass filters and lowpass filters are described using the terms passband, cutoff, and pass. Conceptually, an ideal filter allows signals within the passband to pass through and cuts off signals outside the passband. However, in reality, filters tend to increase attenuation as the signal moves away from the passband, and signals outside the passband are not immediately cut off. For example, in a filter, the frequency at which the signal amplitude is -3 dB below the passband is called the cutoff frequency, and the passband of the filter is expressed by the cutoff frequency. In this specification, the behavior of a signal within the passband defined by the cutoff frequency is described as pass, and the behavior of a signal outside the passband defined by the cutoff frequency is described as cutoff.

[0084] In the above embodiment, 30 kHz was used as an example to describe the predetermined frequency used in carrier sense operation to detune from the frequency at which the received signal strength is measured. The predetermined frequency is not limited to 30 kHz, and any value can be set within the passband of the third BPF114. For example, it could be 50 kHz or 100 kHz.

[0085] In the above embodiment, the case where the local oscillator 101 outputs a 910 MHz signal in a carrier sense operation measuring 916.8 MHz was described as an example, that is, the case where the local oscillator 101 outputs a signal with a frequency lower than the frequency measured in the carrier sense operation. The frequency of the signal output by the local oscillator 101 may be higher or lower than the frequency measured in the carrier sense operation, as long as it is outside the passband of the second BPF 111 or antenna 117, and the frequency of the difference between this frequency and the frequency measured in the carrier sense operation is outside the passband of the third BPF 114. For example, in a carrier sense operation measuring 916.8 MHz, the local oscillator 101 may output 930 MHz.

[0086] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0087] 1... Wireless communication device, 100... CPU, 101... Local oscillator, 102... Quadrature modulator, 103... DA converter, 104... Distributor, 105... Switch, 106... First BPF, 107... Power amplifier, 108... LPF, 109... Antenna, 110... Antenna sharer, 111... Second BPF, 112... Low-noise amplifier, 113... Quadrature demodulator, 114... Third BPF, 115... Amplifier, 116... AD converter, 117... Antenna.

Claims

1. A first filter that restricts the input signal to a first passband, An oscillator circuit that outputs a first signal with a frequency outside the first passband, A modulation circuit modulates the first signal to a second signal that detunes a predetermined frequency from the frequency at which the received signal strength is measured, A demodulator that demodulates the signal that has passed through the first filter based on the second signal, A wireless communication device equipped with the following features.

2. When measuring the received signal strength, The oscillator circuit outputs the first signal, The modulation circuit outputs the second signal, The demodulator demodulates the signal that has passed through the first filter based on the second signal. When communicating with external devices, The oscillator circuit outputs a third signal with a frequency within the first passband. The demodulator demodulates the signal that has passed through the first filter based on the third signal. The wireless communication device according to claim 1.

3. The wireless communication device according to claim 1, wherein the first filter includes a bandpass filter circuit that limits the input signal to a first passband and outputs it.

4. The wireless communication device according to claim 1, wherein the first filter is implemented by an antenna that functions within the first passband and does not function outside the first passband.

5. The system further includes a second filter that limits the input signal to a second passband that does not include the frequency of the difference between the frequency of the first signal and the frequency of the second signal, The wireless communication device according to claim 1, wherein the output of the demodulator is input to the second filter.

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