Non-contact communication device, control method and program

Abstract

An IC card (500) of the present invention comprises: a coil antenna (501) that receives power from a transmission / reception device via non-contact communication; a resonance frequency variable circuit (502) for varying a resonance frequency of the coil antenna (501); a rectification unit (505) that rectifies an antenna output current output from the coil antenna (501); a control unit (508) that consumes a load current; a detection unit (507) that detects an excessive current which is a difference between the load current and a rectified output current output from the rectification unit (505); and a resonance frequency control unit (509) that changes the resonance frequency of the coil antenna (501) by controlling the resonance frequency variable circuit (502) in accordance with a detection signal which indicates a detection result of the excessive current and which is output from the detection unit (507).

Description

Non-contact communication device, control method and program

[0001] The present invention relates to a contactless communication device or the like that is a contactless IC responder called a contactless IC card or IC tag, which performs contactless data communication via electromagnetic waves with an interrogator such as a reader / writer.

[0002] In recent years, the use of contactless IC transponders such as contactless IC cards or IC tags that transmit and receive data without contact has increased, and standardization of communication methods, etc. For example, there are standards such as ISO 14443 for proximity-type contactless IC transponders with a communication distance of about 10 cm, and ISO 15693 for nearby-type contactless IC transponders with a communication distance of about 70 cm.

[0003] This type of contactless IC card is being increasingly adopted for a variety of purposes, such as commuter passes, credit cards, and passports.

[0004] FIG. 1 is a schematic diagram of a conventional IC card system using an IC card.

[0005] FIG. 1 shows a configuration diagram of an IC card 111 and a reader / writer 101. For example, the reader / writer 101 includes a transmitter 102, a receiver 103, a coil antenna 104, and a resonance capacitor 105. For example, the IC card 111 includes a coil antenna 112, a resonance capacitor 113, a rectifier 114, and a load circuit 115. In the IC card system shown in FIG. 1 , power and signals are transmitted and received between the reader / writer 101 and the IC card 111 by electromagnetic induction using electromagnetic waves. More specifically, when the reader / writer 101 transmits electromagnetic waves in which a data signal is superimposed on a carrier wave of a predetermined frequency, a voltage is induced across the coil antenna 112, which constitutes a resonance circuit, in the IC card 111 by electromagnetic induction. This voltage is rectified by the rectifier 114 and used as a power supply voltage Vcc to operate the load circuit 115, and a data signal is extracted and subjected to various processes.

[0006] FIG. 2 is a diagram showing the relationship between the resonant frequency and the voltage between the coil ends for one IC card.

[0007] The voltage induced across both ends of the coil antenna 112 is highest at V1 when the resonant frequency f0 of the resonant circuit is equal to the carrier frequency fc of the received electromagnetic wave, as shown in Figure 2. The resonant frequency f0 is expressed as follows:

[0008] f0=1 / {2×π×√(L×C)}

[0009] Here, L is the inductance of the coil antenna 112 , and C is the capacitance of the resonance capacitor 113 .

[0010] Therefore, when the IC card 111 is manufactured, the inductance of the coil antenna 112 and the capacitance of the resonance capacitor 113 are set so that the resonance frequency f0 is equal to the carrier frequency fc.

[0011] In such an IC card system, it is possible to read data from multiple IC cards at once. However, when multiple IC cards are stacked, a difference in resonance frequency occurs, making it difficult to reliably read data in the conventional IC card system.

[0012] 3 is a schematic diagram of a card system using conventional IC cards when two IC cards are placed close to each other. Like the IC card 111, the IC card 211 includes a coil antenna 212, a resonance capacitor 213, a rectifier 214, and a load circuit 215.

[0013] When the coil antenna 112 and the coil antenna 212 are close to each other as shown in Fig. 3, the resonant frequency decreases due to the mutual inductance M caused by the coupling relationship shown in Fig. 3. Specifically, the resonant frequency f1 of each of the resonant circuits of the two IC cards 111 and 211 is as follows:

[0014] f1=1 / [2×π×√{(L+M)×C}]

[0015] Here, L is the inductance of the coil antennas 112 and 212, C is the capacitance of the resonance capacitors 113 and 213, and M is the mutual inductance.

[0016] FIG. 4 is a diagram showing the relationship between the resonant frequency and the voltage between the coil ends when two IC cards are used.

[0017] The voltage induced in the coil antennas 112 and 212 drops to V2 as shown in Figure 4. This drop in induced voltage becomes more pronounced the more IC cards are nearby and the closer the IC cards are to each other. If the voltage drops below the minimum operable voltage Vo of the IC cards 111 and 211, communication with the reader / writer 101 becomes impossible.

[0018] To avoid this problem, a method has been proposed in which a plurality of resonant capacitance elements are provided and selectively switched to correct the resonant frequency (see, for example, Patent Documents 1 and 2).

[0019] JP 2000-151480 A JP 2007-228621 A

[0020] However, in the resonance frequency correction methods disclosed in Patent Documents 1 and 2, the resonance frequency is corrected when it is detected that the induced voltage exceeds the minimum voltage Vo at which the IC card can operate. However, changing the resonance frequency reduces the induced voltage across the coil antenna, resulting in a decrease in the power supply voltage Vcc. Furthermore, when the load current fluctuates due to the transmission or reception operation of the IC card, the power supply voltage Vcc also decreases. In other words, when the induced voltage decreases due to a change in the resonance frequency, or when the load current increases due to the transmission or reception operation of the IC card, it is not guaranteed that the minimum voltage Vo at which the IC card can operate can be maintained, resulting in unstable operation of the IC card.

[0021] Therefore, the present invention provides a contactless communication device, etc., which can maintain the minimum voltage at which an IC card can operate when the resonant frequency is corrected, regardless of whether the IC card is in a single state or in a state where multiple IC cards are stacked, thereby ensuring stable operation of the IC card.

[0022] The non-contact communication device of the present invention comprises an antenna unit that receives power from a transmitting / receiving device via non-contact communication, a resonant frequency variable circuit for changing the resonant frequency of the antenna unit, a rectifier unit that rectifies the antenna output current output from the antenna unit, a load circuit unit that consumes a load current, a detection unit that detects an excess current which is the difference between the rectified output current output from the rectifier unit and the load current, and a resonant frequency control unit that changes the resonant frequency of the antenna unit by controlling the resonant frequency variable circuit in accordance with a detection signal indicating the detection result of the excess current output from the detection unit.

[0023] The control method of the present invention is a control method for a contactless communication device, wherein the contactless communication device comprises an antenna unit that receives power from a transmitting / receiving device via contactless communication, a resonant frequency variable circuit for changing the resonant frequency of the antenna unit, a rectifier unit that rectifies the antenna output current output from the antenna unit, a load circuit unit that consumes a load current, and a detection unit that detects an excess current which is the difference between the rectified output current output from the rectifier unit and the load current, and the control method includes a step of acquiring a detection signal indicating the detection result of the excess current output from the detection unit, and a step of changing the resonant frequency of the antenna unit by controlling the resonant frequency variable circuit in accordance with the detection signal.

[0024] A program according to the present invention is a program for causing a computer to execute the above control method.

[0025] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0026] According to a non-contact communication device of one aspect of the present invention, whether the IC card is in a single state or in a state where multiple IC cards are stacked, the minimum voltage at which the IC card can operate can be maintained when the resonant frequency is corrected, thereby ensuring stable operation of the IC card.

[0027] 1 is a schematic configuration diagram of an IC card system using a conventional IC card. FIG. 2 is a relationship diagram between the resonant frequency and the voltage between the coil ends for one IC card. FIG. 3 is a schematic configuration diagram of a card system using a conventional IC card when two IC cards are close to each other. FIG. 4 is a relationship diagram between the resonant frequency and the voltage between the coil ends for two IC cards. FIG. 5 is a configuration diagram of a contactless IC card according to embodiment 1. FIG. 6 is a configuration diagram of a variable resonant frequency circuit according to embodiment 1. FIG. 7 is a configuration diagram of a rectifier according to embodiment 1. FIG. 8 is a configuration diagram of a power supply according to embodiment 1. FIG. 9 is a configuration diagram of a detector according to embodiment 1. FIG. 10 is a relationship diagram between the distance between one IC card and a reader / writer according to embodiment 1 and the rectified output current. FIG. 11 is a relationship diagram between the distance between two IC cards and a reader / writer according to embodiment 1 and the rectified output current. FIG. 12 is a time chart of control signals controlled by a resonant frequency control unit according to embodiment 1. 1 is a time chart showing the transitions of the rectified output current, the load current, and the power supply voltage when communication is performed between one IC card and a reader / writer according to a first embodiment, which is a time chart of an IC card system having a function of switching the resonance frequency. FIG. 2 is a time chart showing the transitions of the rectified output current, the load current, and the power supply voltage of an IC card system having a function of switching the resonance frequency. FIG. 3 is a configuration diagram of a contactless IC card according to a second embodiment. FIG. 4 is a configuration diagram of a variable resonance frequency circuit according to the second embodiment. FIG. 5 is a configuration diagram of a detection unit according to the second embodiment. FIG. 6 is a relationship diagram between the distance between one IC card and a reader / writer according to the second embodiment and the rectified output current. FIG. 7 is a relationship diagram between the distance between one IC card and a reader / writer according to the second embodiment and the rectified output current. FIG. 8 is a relationship diagram between the distance between two IC cards and a reader / writer according to the second embodiment and the rectified output current. FIG. 9 is a relationship diagram between the distance between two IC cards and a reader / writer according to the second embodiment and the rectified output current. FIG. 10 is a relationship diagram between the resonance frequency and the rectified output current when communication is performed between one IC card and a reader / writer. 10 is a diagram showing the relationship between the resonance frequency and the rectified output current when communication is performed between two IC cards and a reader / writer. FIG. 11 is a diagram showing the configuration of a contactless IC card according to a third embodiment.10 is a time chart when a reader / writer transmits a command to an IC card according to embodiment 3. FIG. 11 is a time chart when a reader / writer transmits a command to an IC card according to embodiment 3. FIG. 12 is a time chart when a reader / writer transmits a command to an IC card other than the IC card according to embodiment 3. FIG. 13 is a flowchart showing an example of a control method according to another embodiment.

[0028] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0029] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, materials, components, component placement and connection configurations, steps, and step sequences shown in the following embodiments are merely examples and are not intended to limit the present invention.

[0030] First Embodiment A contactless communication device according to a first embodiment will be described below.

[0031] FIG. 5 shows a schematic configuration of a contactless IC card 500 according to the first embodiment.

[0032] The IC card 500 is an example of a contactless communication device and includes a coil antenna 501, a variable resonant frequency circuit 502, a receiver 503, a transmitter 504, a rectifier 505, a power supply 506, a detector 507, a controller 508, a resonant frequency controller 509, and a smoothing capacitor 510.

[0033] The coil antenna 501 is an example of an antenna unit that receives power from a transmitting / receiving device through contactless communication. For example, the transmitting / receiving device is a reader / writer.

[0034] The resonant frequency variable circuit 502 is a circuit for changing the resonant frequency of the coil antenna 501. The configuration of the resonant frequency variable circuit 502 is shown in FIG.

[0035] FIG. 6 is a configuration diagram of the variable resonant frequency circuit 502 according to the first embodiment.

[0036] One end of the capacitance element 524 is connected to the terminal VA, and the other end is connected to the terminal VB. Each of the capacitance elements 520 to 523 has one end connected to the terminal VA, and the other end connected to the terminal VB via the switch elements 525 to 528, respectively. The switch elements 525 to 528 are turned on when the control signal CRES[3:0] is at an H level, and turned off when the control signal CRES[3:0] is at an L level, depending on the logic level. An LC resonant circuit is formed by the inductance L of the coil antenna 501 and at least the capacitance element 524 of the capacitance elements 520 to 524 provided in the resonant frequency variable circuit 502.

[0037] The rectifier 505 rectifies the antenna output current output from the coil antenna 501. Specifically, the rectifier 505 rectifies the AC voltage generated between the terminal VA and the terminal VB at both ends of the coil antenna 501 to output a current Irect, which charges the smoothing capacitor 510 and generates the power supply voltage Vcc. The configuration of the rectifier 505 is shown in FIG.

[0038] FIG. 7 is a configuration diagram of the rectification unit 505 according to the first embodiment.

[0039] For example, the rectifier 505 is configured by diode elements 530 to 533 connected in a bridge configuration, and performs full-wave rectification.

[0040] The power supply unit 506 generates a predetermined power supply voltage Vcc to be applied to the control unit 508 from the rectified output current (current Irect) output from the rectifier unit 505. Specifically, the power supply unit 506 includes a shunt power supply circuit that flows a shunt current Is to a ground reference potential Vss in accordance with the input voltage to the power supply unit 506 and the predetermined power supply voltage Vcc. The power supply unit 506 uses the shunt power supply circuit to flow the shunt current Is to the ground reference potential Vss when the power supply voltage Vcc exceeds the predetermined voltage, thereby controlling the power supply voltage Vcc to not exceed the predetermined value. The configuration of the power supply unit 506 is shown in FIG.

[0041] FIG. 8 is a configuration diagram of the power supply unit 506 according to the first embodiment.

[0042] A constant voltage source 540 outputs a predetermined reference voltage VREF, which is input to the positive input terminal of a comparator 541. A voltage Vr is output according to the magnitudes of resistors 543 and 544, which is input to the negative input terminal of the comparator 541. The comparator 541 compares the voltage Vr with the reference voltage VREF and outputs the result to the gate of a P-type MOSFET 542. When the voltage Vr exceeds the reference voltage VREF, the gate voltage Vg of the P-type MOSFET 542 decreases, increasing the shunt current Iss. When the voltage Vr falls below the reference voltage VREF, the gate voltage Vg increases, decreasing the shunt current Iss. This prevents the power supply voltage Vcc from exceeding a predetermined voltage. Note that the resistance values ​​of resistors 543 and 544 are large and the currents flowing through them are very small, so the shunt current Iss is approximately the same as the shunt current Iss.

[0043] The control unit 508 is an example of a load circuit unit that is connected to the power supply unit 506 and consumes the load current Iload.

[0044] The detector 507 detects the surplus current, which is the difference between the current Irect and the load current Iload (specifically, the value obtained by subtracting the load current Iload from the current Irect). The configuration of the detector 507 is shown in FIG.

[0045] FIG. 9 is a diagram showing the configuration of the detection unit 507 according to the first embodiment.

[0046] The detection unit 507 includes a P-type MOSFET 550, which is a current detection circuit that outputs a detection current (current Idet = Iss / n) whose current value correlates with the current value of the shunt current Iss, and a comparator 552 that compares the current value of the detection current with a first detection current threshold and outputs the comparison result as a detection signal (Up / Down signal). The P-type MOSFET 550 is configured so that its gate width is 1 / n of the gate width of the P-type MOSFET 542 shown in FIG. 8. As a result, the current Idet flowing through the P-type MOSFET 550 is 1 / n of the shunt current Iss. The current mirror 554 passes a current equal to the current Ith of the constant current source 553 to a connection node connected to the positive input terminal of the comparator. The voltage at this connection node is defined as voltage Vdet. When the current Idet is greater than the current Ith, the voltage Vdet increases so that the current Idet decreases toward the current Ith (i.e., the potential difference between the power supply voltage Vcc and the voltage Vdet decreases). When the current Idet is smaller than the current Ith, the voltage Vdet decreases so that the current Idet increases toward the current Ith (i.e., the potential difference between the power supply voltage Vcc and the voltage Vdet increases). The comparator 552 compares the voltage Vdet with the voltage VREF output from the constant voltage source 551 and outputs an UpDown signal. When the voltage Vdet is greater than the voltage VREF, the comparator 552 outputs an UpDown signal with a logic high level. When the voltage Vdet is smaller than the voltage VREF, the comparator 552 outputs an UpDown signal with a logic low level. This configuration of the detector 507 makes it possible to detect whether the current Idet=Iss / n is greater than the current Ith or less than the current Ith. When the current Isr and current Idet flowing through the resistance elements 543 and 544 are designed to be sufficiently smaller than the load current Iload consumed by the control unit 508, the shunt current Iss is expressed as follows:

[0047] Iss≒Irect-Iload

[0048] The shunt current Iss is a surplus current that is the difference between the current Irect supplied by the rectification unit 505 and the load current Iload consumed by the control unit 508 .

[0049] The receiver 503 detects the voltage amplitude generated between terminals VA and VB and outputs a demodulated signal RX. The transmitter 504 changes the impedance between terminals VA and VB in accordance with the transmission data TX and transmits the transmission data to the reader / writer. The controller 508 performs predetermined processing in accordance with the demodulated signal RX and outputs predetermined response data as transmission data TX. The controller 508 also detects that the demodulated signal RX has a predetermined pattern and outputs a HOLD signal that controls the execution and suspension of the operation of the resonant frequency controller 509 (specifically, the operation of changing the resonant frequency of the coil antenna 501).

[0050] The resonant frequency control unit 509 changes the resonant frequency of the coil antenna 501 by controlling the resonant frequency variable circuit 502 in accordance with a detection signal (UpDown signal) indicating the detection result of the surplus current output from the detection unit 507. Specifically, the resonant frequency control unit 509 controls the control signal CRES[3:0] in accordance with the UpDown signal and holds the control signal CRES[3:0] in accordance with the HOLD signal.

[0051] FIG. 10 is a diagram showing the relationship between the distance d between one IC card 500 and the reader / writer according to the first embodiment and the rectified output current (current Irect).

[0052] The load current Iload is the current consumed by the IC card 500, and when the rectified output current exceeds the load current Iload, the IC card 500 starts operating (distance ds0). When the IC card 500 starts operating, the control signal CRES[3:0] is set to 0b1111, and the capacitance Cr0 of the capacitive elements 520 to 523 and the capacitance Crf of the capacitive element 524 are set to satisfy the following equation so that the resonant frequency of the coil antenna 501 at the start of the IC card 500 operation roughly matches the carrier frequency fc.

[0053] fc≒fds01=1 / {2×π×√(L×(Cr0×4+Crf))}

[0054] When the distance d becomes smaller than the distance ds0, the current Irect increases. When the distance d becomes the distance ds1 and the current Irect exceeds the threshold Ith×n (first detection current threshold), the UpDown signal becomes H level, the control signal CRES[3:0] transitions to 0b0111, and the resonant frequency increases to fds12 as shown below.

[0055] fds12=1 / {2×π×√(L×(Cr0×3+Crf))}

[0056] Similarly, the resonant frequency is given by the following with respect to the distance d:

[0057] ds0>=d>=ds1: fds01=1 / {2×π×√(L×(Cr0×4+Crf))} ds1>=d>=ds2: fds12=1 / {2×π×√(L×(Cr0×3+Crf))} ds2>=d>=ds3: fds23=1 / {2×π×√(L×(Cr0×2+Crf))} ds3>=d>=ds4: fds34=1 / {2×π×√(L×(Cr0×1+Crf))} ds4>=d:fds45=1 / {2×π×√(L×(Cr0×0+Crf))}

[0058] In the section from distance ds1 to distance ds4, the current Irect changes in accordance with the change in the resonant frequency. By setting the threshold value Ith×n to a value greater than dImax, which is the maximum value of the change in the current Irect shown in Figure 10, it is possible to satisfy Irect > Iload even if the resonant frequency is shifted, and therefore it is possible to prevent the power supply voltage of the IC card 500 from becoming unstable.

[0059] 11A and 11B are diagrams showing the relationship between the distance d between the two IC cards 500 and the reader / writer according to embodiment 1 and the rectified output current (current Irect). Fig. 11A shows the relationship when the two IC cards 500 approach the reader / writer, and Fig. 11B shows the relationship when the two IC cards 500 move away from the reader / writer. First, the case where the two IC cards 500 approach the reader / writer will be described.

[0060] 11A, when the rectified output current exceeds the load current Iload, the IC card 500 starts operating (distance dm0). When the IC card 500 starts operating, the control signal CRES[3:0] is set to 0b1111. When the distance d becomes smaller than the distance dm0, the current Irect increases. When the distance d becomes dm1 and the current Irect exceeds the threshold Ith×n (first detection current threshold), the UpDown signal becomes H level, the control signal CRES[3:0] transitions to 0b0111, and the resonant frequency of the coil antenna 501 increases to fdm12 as shown below.

[0061] fdm12=1 / {2×π×√((L+M)×(Cr0×3+Crf))}

[0062] Because the resonant frequency fdm01 is smaller than the carrier frequency fc when the distance d is between distances dm0 and dm1, the value of the current Irect at the resonant frequency fdm12 is greater than the value of the current Irect at the resonant frequency fdm01. As described above, the resonant frequency of the coil antenna 501 is set to approximately match the carrier frequency fc when the IC card 500 starts operating, and the resonant frequency decreases when multiple IC cards 500 are stacked. Therefore, even after the resonant frequency transitions to fdm12, the current Irect remains greater than the threshold value Ith×n, so the resonant frequency transitions almost instantaneously from fdm12 to fdm23, fdm34, and fdm45 in that order. The resonant frequencies are as follows for the distance d:

[0063] dm0>=d>=dm1:fdm01=1 / {2×π×√((L+M)×(Cr0×4+Crf))} d=dm1:fdm12=1 / {2×π×√((L+M)×(Cr0×3+Crf))} d=dm1:fdm23=1 / {2×π×√((L+M)×(Cr0×2+Crf))} d=dm1:fdm34=1 / {2×π×√((L+M)×(Cr0×1+Crf))} dm1>=d: fdm45=1 / {2×π×√((L+M)×(Cr0×0+Crf))}

[0064] By setting the capacitance Crf so that the resonant frequency fdm45 when there are two IC cards 500 roughly matches the carrier frequency fc, the IC card 500 can be operated with the resonant frequency and carrier frequency fc matched when the distance d is shorter than the distance dm1.

[0065] At the distance dm1, the current Irect increases as shown in FIG. 11A in response to changes in the resonant frequency, so Irect>Iload is satisfied and the power supply voltage of the IC card 500 does not become unstable.

[0066] Next, a case where two IC cards 500 move away from the reader / writer will be described.

[0067] 11B , as the IC card 500 moves farther away from the reader / writer, the current Irect decreases, the distance d becomes dm1B, and when the current Irect falls below the threshold Ith×n, the UpDown signal goes low, the control signal CRES[3:0] transitions from 0b0000 to 0b0001, and the resonant frequency drops from fdm45 to fdm34. Because the resonant frequency fdm45 roughly coincides with the carrier frequency fc, the value of the current Irect at the resonant frequency fdm34, which is shifted from the carrier frequency fc, is smaller than the value of the current Irect at the resonant frequency fdm45. Therefore, even after the resonant frequency transitions to fdm34, the current Irect remains smaller than the threshold Ith×n, and the resonant frequency transitions almost instantaneously from fdm45 to fdm34, fdm23, and fdm12, in that order. The resonance frequency is given by the following with respect to the distance d:

[0068] dm0>=d>=dm1B: fdm01=1 / {2×π×√((L+M)×(Cr0×4+Crf))} d=dm1B: fdm12=1 / {2×π×√((L+M)×(Cr0×3+Crf))} d=dm1B:fdm23=1 / {2×π×√((L+M)×(Cr0×2+Crf))} d=dm1B:fdm34=1 / {2×π×√((L+M)×(Cr0×1+Crf))} dm1B>=d: fdm45=1 / {2×π×√((L+M)×(Cr0×0+Crf))}

[0069] At a distance dm1B, the current Irect changes in accordance with a change in the resonant frequency. By setting the threshold value Ith×n to a value greater than dImB, which is the amount of change in the current Irect shown in FIG. 11B, Irect>Iload can be satisfied even if the resonant frequency is shifted, and therefore the power supply voltage of the IC card 500 can be prevented from becoming unstable.

[0070] In this way, the resonant frequency control unit 509 may control the resonant frequency variable circuit 502 to lower the resonant frequency of the coil antenna 501 when the detection signal (UpDown signal) of the detection unit 507 indicates that the current value of the detection current (current Idet) correlated with the shunt current Iss is less than the first detection current threshold (Ith×n), and may control the resonant frequency variable circuit 502 to raise the resonant frequency of the coil antenna 501 when the detection signal (UpDown signal) of the detection unit 507 indicates that the current value of the detection current (current Idet) is greater than the first detection current threshold (Ith×n).

[0071] The shunt current Iss is a current corresponding to the surplus current, and the value of the detection current (current Idet) correlates with the current value of the surplus current. The value of current Idet increases as the distance d between the IC card 500 and the reader / writer decreases. In other words, the value of current Idet decreases as the distance d between the IC card 500 and the reader / writer increases. For example, when the IC card 500 starts operating independently, the resonant frequency of the coil antenna 501 is set to the minimum resonant frequency fds01 that can be changed by the resonant frequency variable circuit 502, and this minimum value fds01 is set to the carrier frequency fc. Furthermore, the threshold value Ith×n is set to a value corresponding to a sufficient surplus current.

[0072] When the IC card 500 is brought close to a reader / writer in a standalone state, the current value of the current Idet gradually increases, and when it exceeds the threshold value Ith×n, the resonant frequency is raised. As a result, the resonant frequency deviates from the carrier frequency fc, reducing the excess current. However, even if the excess current decreases slightly from a state in which sufficient current is flowing, the minimum voltage at which the IC card 500 can operate can be maintained. On the other hand, when the IC card 500 is moved away from the reader / writer in a standalone state, the current value of the current Idet gradually decreases, and when it falls below the threshold value Ith×n, the resonant frequency is lowered. As a result, the resonant frequency approaches the carrier frequency fc, increasing the excess current, and the minimum voltage at which the IC card 500 can operate can be maintained.

[0073] When multiple IC cards 500 are stacked, the resonant frequency of the coil antenna 501 is lower than when each IC card 500 is alone. Therefore, when multiple IC cards 500 are stacked and brought closer to a reader / writer, the resonant frequency of the IC cards 500 at the start of operation is lower than the carrier frequency fc. When multiple IC cards 500 are stacked and brought closer to a reader / writer, the current value of the current Idet gradually increases, and when it exceeds the threshold value Ith×n, the resonant frequency is raised. As a result, the resonant frequency approaches the carrier frequency fc, increasing the excess current, and the minimum voltage at which the IC cards 500 can operate can be maintained. On the other hand, when multiple IC cards 500 are stacked and moved away from the reader / writer, the current value of the current Idet gradually decreases, and when it falls below the threshold value Ith×n, the resonant frequency is lowered. As a result, the resonant frequency deviates from the carrier frequency fc and the surplus current decreases, but even if the surplus current decreases slightly from the state in which a sufficient amount of current is flowing, the minimum voltage at which the IC card 500 can operate can be maintained.

[0074] As a result, whether the IC card 500 is in a single state or in a state where multiple IC cards are stacked, when the resonant frequency is corrected, the minimum voltage at which the IC card 500 can operate can be maintained, thereby ensuring stable operation of the IC card 500.

[0075] For example, the threshold value Ith×n may be a value greater than the difference between the current Irect before and after the resonant frequency of the coil antenna 501 is changed.

[0076] In this way, by setting the threshold value Ith×n to a value greater than the difference in current Irect caused by changing the resonant frequency, it is possible to prevent excess current from being generated by changing the resonant frequency, that is, to prevent the IC card 500 from being able to maintain the minimum voltage at which it can operate.

[0077] FIG. 12 is a time chart of the control signal CRES[3:0] controlled by the resonance frequency control unit 509 according to the first embodiment.

[0078] The RF (electromagnetic wave) signal shows the envelope waveform of the electromagnetic wave transmitted from the reader / writer, and data is transmitted to the IC card 500 by AM modulation. Figure 12 shows an example in which data is encoded using Manchester. Also shown is an example of a communication standard in which specific pre-data is transmitted before a command is transmitted.

[0079] When the IC card 500 receives the command following the pre-data (data consisting of 48 consecutive 0 bits in this embodiment), it processes the data according to the command and transmits response data.

[0080] The clock signal CLK_d is a signal that samples the Up / Down signal and has a sampling period t_CLK. While the logic level of the HOLD signal is low, the state of the control signals CRES[3:0] is updated according to the state of the Up / Down signal at the rising edge of the clock signal CLK_d. While the logic level of the HOLD signal is high, the state of the control signals CRES[3:0] is maintained.

[0081] In this embodiment, the IC card 500 performs control to transition the HOLD signal to H level after receiving a demodulated signal RX of 0 four times in a row, and performs control to transition the HOLD signal to L level after transmitting response data. AM modulation is performed at a period of the data rate t_EU.

[0082] When the control signal CRES[3:0] transitions and the resonant frequency changes, the envelope waveform of the RF signal is affected. If the control signal CRES[3:0] transitions while the reader / writer is transmitting data, the demodulation signal RX changes, raising concerns that the IC card 500 may not be able to correctly receive the transmitted data from the reader / writer. Furthermore, if the control signal CRES[3:0] transitions while the reader / writer is receiving a response from the IC card 500, the envelope waveform of the RF signal is affected, raising concerns that the reader / writer may not be able to correctly receive the response from the IC card 500. These concerns will now be explained using FIG. 13 .

[0083] FIG. 13 is a time chart of an IC card system having a function for switching the resonant frequency.

[0084] The RF (electromagnetic wave) signal shows the envelope waveform of the electromagnetic wave transmitted from the reader / writer, and data is sent to the IC card by AM modulation. Figure 13 shows an example in which data is encoded using Manchester. It also shows an example of a communication standard in which specific pre-data is transmitted before a command is transmitted. The demodulated signal RX is the internal signal of the IC card obtained by demodulating the RF signal, and the transmitted data TX is response data that the IC card transmits to the reader / writer in response to a command. Figure 13 shows a state in which the resonant frequency changes periodically from fa0 to fa1, fa2, fa3, and fa4. When the resonant frequency changes, the impedance between terminals VA and VB changes, and the envelope of the RF (electromagnetic wave) signal changes. If the resonant frequency changes while the IC card is performing a receiving operation, the times at which transmitted data may not be received correctly are shown as t_fa1, t_fa2, and t_fa3 in Figure 13. There is a concern that the influence of changes in impedance between terminals VA and VB will be superimposed on the AM-modulated waveform of the RF signal, preventing correct demodulation. Also, t_fa4 in Figure 13 shows the time at which a response may not be received correctly if the resonant frequency changes while the IC card is transmitting response data. There is a concern that the influence of changes in impedance between terminals VA and VB will be superimposed on the AM-modulated waveform of the RF signal, preventing the response data from being erroneously transmitted to the reader / writer.

[0085] For this reason, it is desirable not to change the resonant frequency during the period when data is transmitted from the reader / writer and the period when the IC card 500 transmits a response.

[0086] For example, by setting the sampling period t_CLK to 4×t_EU or more, a period in which the control signal CRES[3:0] does not change can be set to 4×t_EU or more, and by transitioning the HOLD signal to H level before a command is sent from the reader / writer, the resonant frequency can be prevented from changing.

[0087] In this way, receiving unit 503 receives data based on the signal obtained from coil antenna 501, and control unit 508 controls, in accordance with the data, whether resonant frequency control unit 509 executes or stops the operation of changing the resonant frequency of coil antenna 501. If the resonant frequency of coil antenna 501 changes while IC card 500 is receiving data from a reader / writer, there is a risk that the data may not be received correctly, so the operation of changing the resonant frequency can be stopped while data is being received.

[0088] Figure 14 is a time chart showing the changes in the rectified output current (current Irect), the load current Iload (Icc or Istb), and the power supply voltage Vcc when communication is taking place between one IC card 500 according to embodiment 1 and a reader / writer.

[0089] The RF (electromagnetic wave) signal shows the envelope waveform of the electromagnetic wave transmitted from the reader / writer, and data is sent to IC card 500 by AM modulation. At time t_fc0, it is detected that the excess current (current Irect - load current Iload) is greater than the first detection current threshold (threshold Ith x n), and the resonant frequency transitions from fds34 to fds45. The current Irect is lower after the transition to fds45 than when the resonant frequency is fds34. During the period from time t_fc1 to time t_fc2, IC card 500 receives a command, and after time t_fc2, data processing begins, and the load current Iload increases from Istb to Icc.

[0090] When the reader / writer transmits an AM modulated signal (command) and the receiver 503 receives the command, the load current Iload increases in response to the command. If this change (Icc-Istb) is greater than the detection current threshold (Ith×n) for the detection current (current Idet), the current Irect falls below the load current Iload, causing a drop in the power supply voltage Vcc and resulting in unstable operation of the IC card 500.

[0091] This problem will be explained with reference to FIG.

[0092] FIG. 15 is a time chart showing the transitions of the rectified output current (current Irect), the load current Iload, and the power supply voltage Vcc of an IC card system having a function of switching the resonant frequency.

[0093] The RF (electromagnetic wave) signal shows the envelope waveform of the electromagnetic wave transmitted from the reader / writer, and data is sent to the IC card by AM modulation. At time t_fb0, it is detected that voltage Vcc is greater than voltage Vo, and the resonant frequency transitions from fb0 to fb1. If the resonant frequency fb0 is the same as the carrier frequency fc, the current Irect decreases. The IC card receives a command between time t_fb1 and time t_fb2, and data processing begins after time t_fb2, causing the load current Iload to increase from Istb to Icc.

[0094] At this time, if the current Irect falls below Icc, the power supply voltage Vcc cannot maintain the minimum voltage Vo at which the IC card can operate, and the IC card stops operating. Conventional methods of changing the resonant frequency depending on the power supply voltage, etc., have the problem that the rectified output current required when the operating current suddenly increases cannot be maintained.

[0095] In contrast, by setting the current Ith as follows, taking into account the operating current of the IC card 500, even if the operating current of the IC card 500 suddenly increases due to a change in the resonant frequency, it is possible to prevent the current Irect from falling below the load current Iload, as shown in Figure 14, thereby enabling stable operation of the IC card 500.

[0096] Ith>{(Icc-Istb)+dImax} / n dImax=Irect_fc34-Irect_fc45

[0097] In this way, the control unit 508 may have at least a first state (where the current value of the load current Iload is Istb) and a second state (where the current value of the load current Iload is Icc), and the resonant frequency variable circuit 502 may be a circuit for changing the resonant frequency of the coil antenna 501 to at least a fifth resonant frequency and a sixth resonant frequency. For example, the fifth resonant frequency is one of the resonant frequencies fds01 to fds34, and the sixth resonant frequency is a resonant frequency higher than the fifth resonant frequency of the resonant frequency fds12 to fds45. The first detection current threshold may be greater than the sum of the value obtained by subtracting the current value of the rectified output current when the resonant frequency of the coil antenna 501 is the sixth resonant frequency from the current value of the rectified output current when the resonant frequency of the coil antenna 501 is the fifth resonant frequency, and the value obtained by subtracting the load current Iload (Istb) in the first state from the load current Iload (Icc) in the second state.

[0098] In the IC card 500, when data processing is being performed by the control unit 508 (second state), the load current Iload is larger than when data processing is not being performed by the control unit 508 (first state). Therefore, by setting the first detection current threshold in consideration of the load current Iload (Icc) in the second state, it is possible to prevent excess current from being generated due to a change in the resonant frequency, in other words, to prevent the IC card 500 from being unable to maintain the minimum voltage at which it can operate.

[0099] In addition to the first state and the second state, the control unit 508 may have a state in which the load current Iload is different from the load current Iload in the first state and the second state.

[0100] In the above-described first embodiment, whether the IC card 500 is in a single state or in a state where multiple IC cards are stacked, unless a certain amount of surplus current is generated, the resonant frequency of the coil antenna 501 is not changed (corrected). In other words, the generation of a certain amount of surplus current causes the correction of the resonant frequency of the coil antenna 501. Therefore, whether the IC card 500 is in a single state or in a state where multiple IC cards are stacked, the minimum voltage at which the IC card 500 can operate can be maintained when the correction of the resonant frequency is performed, thereby ensuring stable operation of the IC card 500. Consequently, stable operation of transmission and reception between the IC card 500 and the reader / writer can be ensured. This also applies to the second and third embodiments described below.

[0101] Second Embodiment FIG. 16 is a diagram showing the configuration of a contactless IC card 500a according to a second embodiment.

[0102] The IC card 500a differs from the IC card 500 according to the first embodiment in that it includes a resonant frequency variable circuit 511, a detection unit 513, and a resonant frequency control unit 512 instead of the resonant frequency variable circuit 502, the detection unit 507, and the resonant frequency control unit 509. The coil antenna 501, the receiving unit 503, the transmitting unit 504, the rectifying unit 505, the power supply unit 506, the control unit 508, and the smoothing capacitor 510 are the same components as those in the first embodiment, and therefore detailed description thereof will be omitted.

[0103] The configuration of the resonant frequency variable circuit 511 is shown in FIG.

[0104] FIG. 17 is a configuration diagram of a variable resonance frequency circuit 511 according to the second embodiment.

[0105] One end of the capacitance element 524 is connected to the terminal VA, and the other end is connected to the terminal VB. One end of the capacitance element 560 is connected to the terminal VA, and the other end is connected to the terminal VB via the switch element 561. The switch element 561 is turned on when the control signal CRES_S is at an H level, and turned off when the control signal CRES_S is at an L level, depending on the logical level of the control signal CRES_S. An LC resonant circuit is formed by the inductance L of the coil antenna 501 and at least the capacitance element 524 of the capacitance elements 524 and 560 provided in the resonant frequency variable circuit 511.

[0106] The resonance frequency control section 512 controls the control signal CRES_S in response to the Up / Down signal and holds the control signal CRES_S in response to the HOLD signal.

[0107] The configuration of the detection unit 513 is shown in FIG.

[0108] FIG. 18 is a diagram showing the configuration of the detection unit 513 according to the second embodiment.

[0109] The P-type MOSFET 550, constant voltage source 551, comparator 552, constant current source 553, and current mirror 554 are the same components as those in the first embodiment, and detailed description thereof will be omitted. The constant current source 555 is a low constant current source that supplies a current Iths having a current value smaller than the current Ith. The switch elements 556 and 557 are controlled to be turned on or off depending on the state of the UpDown signal. When the UpDown signal is at an L level, the switch element 556 is turned on and the switch element 557 is turned off. When the UpDown signal is at an H level, the switch element 557 is turned on and the switch element 556 is turned off.

[0110] 19A and 19B are diagrams showing the relationship between the distance d between one IC card 500a and the reader / writer and the rectified output current (current Irect) according to embodiment 2. Fig. 19A shows the relationship when the IC card 500a approaches the reader / writer, and Fig. 19B shows the relationship when the IC card 500a moves away from the reader / writer. First, the case where one IC card 500a approaches the reader / writer will be described.

[0111] 19A, when the rectified output current exceeds the load current Iload, the IC card 500a starts operating (distance dss0). When the IC card 500a starts operating, the control signal CRES_S is set to 0b1, and the capacitance Cr_S of the capacitive element 560 and the capacitance Crf_S of the capacitive element 524 are set to satisfy the following equation so that the resonant frequency of the coil antenna 501 approximately matches the carrier frequency fc.

[0112] fc≒fdss01=1 / {2×π×√(L×(Cr_S+Crf_S))}

[0113] When the distance d becomes smaller than the distance dss0, the current Irect increases. When the distance d becomes the distance dss1 and the current Irect exceeds the threshold value Ith×n (first detection current threshold), the UpDown signal changes from the L level to the H level, the control signal CRES_S transitions to 0b0, and the resonant frequency increases to the following fdss12.

[0114] fdss12=1 / {2×π×√(L×Crf_S)}

[0115] When the Up / Down signal transitions from L level to H level, the switch element 556 of the detection unit 513 is turned off, the switch element 557 is turned on, and the input current to the current mirror 554 is changed from the current Ith to the current Iths. This makes it possible to prevent the Up / Down signal from chattering.

[0116] At the distance dss1, the current Irect changes in accordance with the change in the resonant frequency. By setting the threshold value Ith×n to a value greater than dIs, which is the amount of change in the current Irect shown in FIG. 19A, Irect>Iload can be satisfied even if the resonant frequency is shifted, and therefore the power supply voltage of the IC card 500a can be prevented from becoming unstable.

[0117] Next, a case where one IC card 500a moves away from the reader / writer will be described.

[0118] 19B, as the IC card 500a moves away from the reader / writer, the current Irect decreases, the distance d becomes distance dss1B, and when the current Irect falls below the threshold Iths×n (second detection current threshold), the UpDown signal goes low, the control signal CRES_S transitions from 0b0 to 0b1, the resonant frequency drops from fdss12 to fdss01, and the current Irect increases. At the distance dss1B where the resonant frequency switches, the current Irect does not fall below the load current Iload, and the power supply voltage of the IC card 500a does not become unstable.

[0119] 20A and 20B are diagrams showing the relationship between the distance d between two IC cards 500a and a reader / writer and the rectified output current (current Irect) according to embodiment 2. Fig. 20A shows the relationship when the two IC cards 500a approach the reader / writer, and Fig. 20B shows the relationship when the two IC cards 500a move away from the reader / writer. First, the case where the two IC cards 500a approach the reader / writer will be described.

[0120] As shown in Figure 20A, when the rectified output current exceeds the load current Iload, the IC card 500a begins operating (distance dms0). When the IC card 500a begins operating, the control signal CRES_S is set to 0b1. When the distance d becomes smaller than the distance dms0, the current Irect increases. When the distance d becomes dms1 and the current Irect exceeds the threshold Ith x n (first detection current threshold), the UpDown signal becomes H level, the control signal CRES_S transitions to 0b0, and the resonant frequency of the coil antenna 501 increases to fdms12 as shown below.

[0121] fdms12=1 / {2×π×√((L+M)×(Cr0×3+Crf))}

[0122] When the UpDown signal transitions from L level to H level, the switch element 556 is turned off, the switch element 557 is turned on, and the input current to the current mirror 554 is changed from the current Ith to the current Iths. The resonant frequency is controlled according to the distance d as follows:

[0123] dms0<=d<=dms1:fdms01=1 / {2×π×√((L+M)×(Cr_S+Crf_S))} d<=dms1:fdms12=1 / {2×π×√((L+M)×Crf_S)}}

[0124] By setting the capacitance Crf_S so that the resonant frequency fdms12 when there are two IC cards 500a is roughly equal to the carrier frequency fc, the IC card 500a can be operated with the resonant frequency and carrier frequency fc equal when the distance d is shorter than the distance dms1.

[0125] Next, a case where two IC cards 500a move away from the reader / writer will be described.

[0126] As shown in Figure 20B, as the IC card 500a moves away from the reader / writer, the current Irect decreases, and the distance d becomes distance dms1B. When the current Irect falls below the threshold Iths x n (second detection current threshold), the UpDown signal goes low, the control signal CRES_S transitions from 0b0 to 0b1, the resonant frequency drops from fdss12 to fdss01, and the current Irect decreases. At the distance dss1B where the resonant frequency switches, the current Irect falls below the load current Iload, and the operation of the IC card 500a stops. When the IC card 500a moves away from the reader / writer, the communication distance can be extended compared to when it moves closer.

[0127] FIG. 21 is a diagram showing the relationship between the resonant frequency and the rectified output current when communication is performed between one IC card 500a and a reader / writer.

[0128] An IC card 500a starts operating with a resonant frequency of f0. f0 is the resonant frequency at which the rectified output current is at its maximum (point A in FIG. 21), maximizing the communication distance of the IC card 500a. When the rectified output current exceeds the first detection current threshold (threshold Ith×n) + the load current Iload of the IC card 500a, control is performed to increase the resonant frequency, and the resonant frequency rises to f0u at point B in FIG. 21. Between points A and B in FIG. 21, the rectified output current decreases, but does not fall below the load current Iload of the IC card 500a. This ensures a minimum operating voltage Vo or higher, enabling stable operation of the IC card 500a.

[0129] FIG. 22 is a diagram showing the relationship between the resonant frequency and the rectified output current when communication is performed between two IC cards 500a and a reader / writer.

[0130] The two IC cards 500a start operation when the resonant frequency is f1. Point A in Fig. 22 indicates the rectified output current when the resonant frequency is f1, and the rectified output current is equal to (first detection current threshold (threshold Ith × n) + load current Iload of IC card 500a).

[0131] When the rectified output current exceeds (first detection current threshold + IC card load current), control is performed to increase the resonant frequency, and it rises to resonant frequency f2 at point B in Fig. 22. By controlling C below to the value of C2 so that resonant frequency f2 is equal to carrier frequency fc, the rectified output current can be maximized, and furthermore, the resonant frequency can be made to match carrier frequency fc, thereby improving transmission characteristics (no null point occurs).

[0132] f1=1 / [2×π×√{(L+M)×C}] f2=1 / [2×π×√{(L+M)×C2}]=fc

[0133] In this way, the resonant frequency variable circuit 511 may be a circuit for changing the resonant frequency of the coil antenna 501 to at least a first resonant frequency and a second resonant frequency, where the second resonant frequency is higher than the first resonant frequency. For example, the first resonant frequency is f0 and the second resonant frequency is f0u. When the IC card 500a receives power solely between the reader / writer and the coil antenna 501, the current Irect is larger when the resonant frequency of the coil antenna 501 is the first resonant frequency than when it is the second resonant frequency.

[0134] For example, suppose the resonant frequency of the coil antenna 501 is set to a first resonant frequency when the IC card 500a starts operating alone. If the resonant frequency of the coil antenna 501 is increased from the first resonant frequency to a second resonant frequency when the IC card 500a is alone, the resonant frequency of the coil antenna 501 deviates from the carrier frequency fc, reducing the current Irect. However, since the resonant frequency is changed while a certain amount of surplus current is generated, the minimum voltage at which the IC card 500a can operate can be maintained. When multiple IC cards 500a are stacked, the resonant frequency of the coil antenna 501 is lower than when each IC card 500a is alone. Therefore, the resonant frequency of the IC cards 500a when multiple IC cards 500a are stacked together when they start operating is lower than the carrier frequency fc. When multiple IC cards 500a are stacked and the resonant frequency of the coil antenna 501 is increased from the first resonant frequency to the second resonant frequency, the resonant frequency of the coil antenna 501 approaches the carrier frequency fc and the current Irect increases, so that the minimum voltage at which the IC cards 500a can operate can be maintained.

[0135] As a result, whether the IC card 500a is in a single state or in a state where multiple IC cards are stacked, when the resonant frequency is corrected, the minimum voltage at which the IC card 500a can operate can be maintained, thereby ensuring stable operation of the IC card 500a.

[0136] Furthermore, the resonant frequency variable circuit 511 may be a circuit for changing the resonant frequency of the coil antenna 501 to at least a third resonant frequency or a fourth resonant frequency. For example, the third resonant frequency is fdss01, and the fourth resonant frequency is fdss12. Furthermore, the comparator 552 of the detection unit 513 may compare the current value of the current Idet with a first detection current threshold (threshold Ith×n), or may compare the current value of the current Idet with a second detection current threshold (threshold Iths×n) that is smaller than the first detection current threshold, and output the comparison result as an Up / Down signal. The resonant frequency control unit 512 may control the resonant frequency variable circuit 511 to change the resonant frequency of the coil antenna 501 to a fourth resonant frequency when the Up / Down signal indicates that the current value of the current Idet is greater than the threshold value Ith×n, and may control the resonant frequency variable circuit 511 to change the resonant frequency of the coil antenna 501 to a third resonant frequency when the Up / Down signal indicates that the current value of the current Idet is equal to or less than the threshold value Iths×n.

[0137] The shunt current Iss is a current corresponding to the surplus current, and the current value of the current Idet correlates with the current value of the surplus current. The closer the distance d between the IC card 500a and the reader / writer, the larger the current value of the current Idet. In other words, the farther the distance d between the IC card 500a and the reader / writer, the smaller the current value of the current Idet. For example, when the IC card 500a starts operating independently, the resonant frequency of the coil antenna 501 is set to a third resonant frequency, and the third resonant frequency is set to the carrier frequency fc. Furthermore, the threshold value Ith×n is set to a value corresponding to a sufficient surplus current.

[0138] When the IC card 500a is brought close to a reader / writer in a standalone state, the current value of the current Idet gradually increases, and when it exceeds the threshold value Ith×n, the resonant frequency is raised to the fourth resonant frequency. As a result, the resonant frequency deviates from the carrier frequency fc, reducing the excess current. However, even if the excess current decreases slightly from a state where sufficient current is flowing, the minimum voltage at which the IC card 500a can operate can be maintained. On the other hand, when the IC card 500a is moved away from the reader / writer in a standalone state, the current value of the current Idet gradually decreases, and when it falls below the threshold value Iths×n, the resonant frequency is lowered to the third resonant frequency. As a result, the resonant frequency approaches the carrier frequency fc, increasing the excess current, and the minimum voltage at which the IC card 500a can operate can be maintained.

[0139] When multiple IC cards 500a are stacked, the resonant frequency of the coil antenna 501 is lower than when each IC card 500a is used alone. Therefore, the resonant frequency of the IC cards 500a when multiple IC cards 500a are stacked is lower than the carrier frequency fc when the IC cards 500a start operating. When multiple IC cards 500a are stacked and brought closer to a reader / writer, the current value of the current Idet gradually increases, and when it exceeds the threshold value Ith×n, the resonant frequency is raised. As a result, the resonant frequency approaches the carrier frequency fc, increasing the excess current, and the minimum voltage at which the IC cards 500a can operate can be maintained. On the other hand, when multiple IC cards 500a are stacked and moved away from the reader / writer, the current value of the current Idet gradually decreases, and when it falls below the threshold value Iths×n, the resonant frequency is lowered. As a result, the resonant frequency deviates from the carrier frequency fc, reducing the surplus current, but because the threshold value Iths×n is smaller than the threshold value Ith×n, the surplus current reduces after the IC card 500a is moved farther away from the reader / writer than when the current value of the current Idet is compared with the threshold value Ith×n. Therefore, when the IC card 500a is moved farther away from the reader / writer, the communication distance between the IC card 500a and the reader / writer can be increased.

[0140] In addition, the threshold value Ith×n may be a value greater than the current value of the current Irect when the resonant frequency of the coil antenna 501 is the third resonant frequency minus the current value of the current Irect when the resonant frequency of the coil antenna 501 is the fourth resonant frequency.

[0141] In this way, by setting the threshold value Ith×n to a value greater than the difference in current Irect generated by changing from the third resonant frequency to the fourth resonant frequency, it is possible to prevent excess current from being generated by changing the resonant frequency, that is, to prevent the IC card 500a from being unable to maintain the minimum voltage at which it can operate.

[0142] Furthermore, in the second embodiment, the number of switch elements in the resonant frequency variable circuit 511 can be reduced compared to the first embodiment, and the circuit area can be reduced.

[0143] Third Embodiment FIG. 23 is a diagram showing the configuration of a contactless IC card 500b according to a third embodiment.

[0144] The IC card 500b differs from the IC card 500a according to the second embodiment in that it includes a control unit 514 and a resonant frequency control unit 515 instead of the control unit 508 and the resonant frequency control unit 512. The coil antenna 501, the receiving unit 503, the transmitting unit 504, the rectifying unit 505, the power supply unit 506, the smoothing capacitor 510, the resonant frequency variable circuit 511, and the detecting unit 513 are the same components as those in the second embodiment, and therefore detailed description thereof will be omitted.

[0145] The control unit 514 performs a predetermined process in response to the demodulated signal RX and outputs predetermined response data as transmission data TX. It also detects that the demodulated signal RX is a predetermined command and outputs a MATCH signal or UNMATCH signal.

[0146] The resonance frequency control section 515 controls the control signal CRES_S in accordance with the UpDown signal and the MATCH signal or UNMATCH signal.

[0147] 24A and 24B are time charts when a reader / writer transmits a command to an IC card 500b (IC card A) according to the third embodiment.

[0148] FIG. 24A shows a time chart when the Up / Down signal is at L level, and FIG. 24B shows a time chart when the Up / Down signal is at H level.

[0149] The RF (electromagnetic wave) signal represents the envelope waveform of the electromagnetic wave transmitted from the reader / writer, and data is transmitted to IC card 500b by AM modulation. The command transmitted from the reader / writer includes an ID unique to IC card 500b, thereby specifying IC card 500b as the target for processing. For example, if the command transmitted from the reader / writer includes the ID of IC card A, IC card A can be specified as the target for processing. When the ID of IC card A matches the ID of the command, the control unit 514 of IC card A outputs a pulse signal that remains high for a predetermined period as a MATCH signal. The resonant frequency control unit 515 controls the control signal CRES_S according to the state of the UpDown signal in synchronization with the rising edge of the MATCH signal. When the UpDown signal is low, the resonant frequency control unit 515 holds (does not change) the control signal CRES_S. When the UpDown signal is at H level, the resonant frequency control unit 515 transitions the control signal CRES_S to L level, thereby increasing the resonant frequency. When the UpDown signal is at H level, the rectified output current (current Irect) is equal to or greater than (load current Iload+threshold value Ith×n). Even after the resonant frequency is changed, the current Irect is greater than the load current Iload, so the operation of the IC card 500b can be stabilized.

[0150] FIG. 25 is a time chart showing a case where a reader / writer transmits a command to an IC card 500b (IC card A) according to the third embodiment for a card other than IC card A. When the ID of IC card A does not match the ID of the command, the control unit 514 of IC card A outputs a pulse signal that remains high for a predetermined period as an UNMATCH signal. The resonant frequency control unit 515 synchronizes with the rising edge of the UNMATCH signal to transition the control signal CRES_S to low, regardless of the state of the Up / Down signal, thereby controlling the increase of the resonant frequency. Since the reader / writer transmits a command to a card other than IC card A, it can be seen that the reader / writer is communicating with two or more IC cards 500b, i.e., the resonant frequency is lower than the carrier frequency fc. In this case, the current Irect can be increased by increasing the resonant frequency to bring the resonant frequency closer to the carrier frequency fc. This allows the current Irect to be greater than the load current Iload, preventing the operation of the IC card 500b from becoming unstable.

[0151] In this way, the control unit 514 determines whether the ID indicated by the received data matches the ID of the IC card 500b, and if they do not match, the resonant frequency control unit 515 performs an operation to change the resonant frequency of the coil antenna 501 regardless of the Up / Down signal.

[0152] When the ID of the card itself matches the ID of the command, it is not possible to determine whether a single IC card 500b is present or multiple IC cards are stacked, and therefore the resonant frequency is changed in response to the Up / Down signal. On the other hand, when the ID of the card itself does not match the ID of the command, multiple IC cards 500b are present (i.e., the resonant frequency is low), and therefore the resonant frequency can be forcibly increased regardless of the Up / Down signal, and the resonant frequency can be brought closer to the carrier frequency fc.

[0153] (Other Embodiments) As described above, embodiments 1, 2, and 3 have been described as examples of the technology according to the present invention. However, the technology according to the present invention is not limited to these, and can be applied to embodiments in which appropriate changes, substitutions, additions, omissions, etc. are made. For example, the following modifications are also included in one embodiment of the present invention.

[0154] In the first, second and third embodiments, a system in which communication takes place between one and two IC cards and a reader / writer is described, but the present invention can also be applied to a system in which communication takes place between three or more IC cards and a reader / writer.

[0155] Furthermore, in the first, second and third embodiments, the control method for increasing the resonant frequency higher than the carrier frequency has been described, but the present invention can also be applied to control for decreasing the resonant frequency.

[0156] Furthermore, in the first, second and third embodiments, the capacitance of the resonant frequency control section is changed as a component for changing the resonant frequency, but the present invention can also be applied to a method for changing the inductance of a coil antenna.

[0157] Furthermore, in the first, second and third embodiments, the IC card is provided with the power supply unit 506 , but the IC card does not necessarily have to be provided with the power supply unit 506 .

[0158] In addition, in the first, second, and third embodiments, the non-contact communication device is an IC card, and the communication system between the IC card and the reader / writer is described, but the present invention can also be applied to resonance frequency control in a general non-contact data communication system. For example, the IC card described in this specification can be replaced with an IC tag.

[0159] Furthermore, in the second and third embodiments, the resonant frequency variable circuit is provided with two capacitance elements, but as in the first embodiment, the number may be three or more.

[0160] For example, the present invention can be realized not only as a non-contact communication device, but also as a control method including steps (processing) performed by components (for example, a resonant frequency control unit) that make up the non-contact communication device.

[0161] FIG. 26 is a flowchart showing an example of a control method according to another embodiment.

[0162] The control method is a control method for a contactless communication device, the contactless communication device comprising an antenna unit that receives power from a transmitting / receiving device via contactless communication, a resonant frequency variable circuit for changing the resonant frequency of the antenna unit, a rectifier unit that rectifies the antenna output current output from the antenna unit, a load circuit unit that consumes a load current, and a detection unit that detects an excess current which is the difference between the rectified output current output from the rectifier unit and the load current, and the control method includes, as shown in Figure 26, a step (step S11) of acquiring a detection signal indicating the detection result of the excess current output from the detection unit, and a step (step S12) of changing the resonant frequency of the antenna unit by controlling the resonant frequency variable circuit in accordance with the detection signal.

[0163] For example, the present invention can be realized as a program for causing a computer (processor) to execute the steps included in the control method. Furthermore, the present invention can be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0164] For example, when the present invention is realized as a program (software), each step is performed by running the program using hardware resources such as a computer's CPU, memory, input / output circuits, etc. In other words, each step is performed by the CPU acquiring data from memory or input / output circuits, etc., performing calculations, and outputting the calculation results to memory or input / output circuits, etc.

[0165] In the above-described embodiment, each component included in the non-contact communication device may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0166] Some or all of the functions of the contactless communication device according to the above embodiments are typically realized as an LSI, which is an integrated circuit. These functions may be individually integrated into a single chip, or some or all of them may be integrated into a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array), which can be programmed after LSI manufacturing, or a reconfigurable processor, which can reconfigure the connections and settings of circuit cells within an LSI, may also be used.

[0167] Furthermore, if an integrated circuit technology that can replace LSIs emerges due to advances in semiconductor technology or other derivative technologies, that technology may naturally be used to integrate the components included in the non-contact communication device.

[0168] In addition, the present invention also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope of the present invention.

[0169] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0170] (Technology 1) A contactless communication device comprising: an antenna unit that receives power from a transmitting / receiving device via contactless communication; a resonant frequency variable circuit that changes the resonant frequency of the antenna unit; a rectifier unit that rectifies an antenna output current output from the antenna unit; a load circuit unit that consumes a load current; a detector unit that detects an excess current that is the difference between the rectified output current output from the rectifier unit and the load current; and a resonant frequency controller that changes the resonant frequency of the antenna unit by controlling the resonant frequency variable circuit in accordance with a detection signal that indicates the detection result of the excess current output from the detector unit.

[0171] According to this, whether the non-contact communication device (for example, an IC card, hereinafter referred to as IC card) is in a single state or in a state where multiple non-contact communication devices are stacked, unless a certain amount of surplus current is generated, the resonant frequency of the antenna unit is not changed (corrected). In other words, the generation of a certain amount of surplus current causes the correction of the resonant frequency of the antenna unit, so whether the IC card is in a single state or in a state where multiple IC cards are stacked, the minimum voltage at which the IC card can operate can be maintained when the correction of the resonant frequency is performed, thereby ensuring stable operation of the IC card.

[0172] (Technology 2) The non-contact communication device according to Technology 1 further includes a power supply unit that generates a predetermined power supply voltage to be applied to the load circuit unit from the rectified output current, the power supply unit including a shunt power supply circuit that flows a shunt current to a ground reference potential in accordance with an input voltage to the power supply unit and the predetermined power supply voltage, the detection unit including a current detection circuit that outputs a detection current whose current value correlates with the current value of the shunt current, and a comparator that compares the current value of the detection current with a first detection current threshold and outputs the comparison result as the detection signal, and the resonant frequency control unit controls the resonant frequency variable circuit to lower the resonant frequency of the antenna unit when the detection signal indicates that the current value of the detection current is equal to or less than the first detection current threshold, and controls the resonant frequency variable circuit to raise the resonant frequency of the antenna unit when the detection signal indicates that the current value of the detection current is greater than the first detection current threshold.

[0173] The shunt current is a current equivalent to the excess current, and the value of the detection current correlates with the value of the excess current. The closer the distance between the IC card and the transmitting / receiving device (e.g., a reader / writer, hereinafter referred to as the reader / writer), the larger the value of the detection current. In other words, the farther the distance between the IC card and the reader / writer, the smaller the value of the detection current. For example, when the IC card starts operating independently, the resonant frequency of the antenna unit is set to the lowest resonant frequency that can be changed by the resonant frequency variable circuit, and this lowest value is set to the carrier frequency. Furthermore, the first detection current threshold is set to a value corresponding to a sufficient excess current.

[0174] When an IC card is brought close to a reader / writer in a standalone state, the current value of the detection current gradually increases, and when it exceeds the first detection current threshold, the resonant frequency is raised. As a result, the resonant frequency deviates from the carrier frequency and the excess current decreases, but even if the excess current decreases slightly from a state in which sufficient current is flowing, the minimum voltage at which the IC card can operate can be maintained. On the other hand, when an IC card is moved away from the reader / writer in a standalone state, the current value of the detection current gradually decreases, and when it falls below the first detection current threshold, the resonant frequency is lowered. As a result, the resonant frequency approaches the carrier frequency and the excess current increases, so the minimum voltage at which the IC card can operate can be maintained.

[0175] When multiple IC cards are stacked, the resonant frequency of the antenna unit is lower than when each IC card is alone, so the resonant frequency of the IC cards when they start operating when multiple IC cards are stacked is lower than the carrier frequency. When multiple IC cards are stacked and brought closer to a reader / writer, the current value of the detection current gradually increases, and when it exceeds the first detection current threshold, the resonant frequency is raised. As a result, the resonant frequency approaches the carrier frequency and the excess current increases, so the minimum voltage at which the IC cards can operate is maintained. On the other hand, when multiple IC cards are stacked and moved away from the reader / writer, the current value of the detection current gradually decreases, and when it falls below the first detection current threshold, the resonant frequency is lowered. As a result, the resonant frequency deviates from the carrier frequency and the excess current decreases, but even if the excess current decreases slightly from a state where it is flowing sufficiently, the minimum voltage at which the IC cards can operate is maintained.

[0176] As a result, whether the IC card is in a single state or in a state where multiple IC cards are stacked, the minimum voltage at which the IC card can operate can be maintained when the resonant frequency is corrected, thereby ensuring stable operation of the IC card.

[0177] (Technology 3) The non-contact communication device according to Technology 2, wherein the first detection current threshold is a value greater than a difference between the rectified output current before and after changing the resonant frequency of the antenna unit.

[0178] In this way, by setting the first detection current threshold to a value greater than the difference in rectified output current caused by a change in the resonant frequency, it is possible to prevent excess current from being generated due to a change in the resonant frequency, that is, to prevent the IC card from being unable to maintain the minimum voltage at which it can operate.

[0179] (Technology 4) The resonant frequency variable circuit is a circuit for changing the resonant frequency of the antenna unit to at least a first resonant frequency and a second resonant frequency, the second resonant frequency is higher than the first resonant frequency, and in a state in which the non-contact communication device receives power solely between the transceiver and the antenna unit, the rectified output current is larger when the resonant frequency of the antenna unit is the first resonant frequency than when it is the second resonant frequency.

[0180] For example, suppose the resonant frequency of the antenna unit when an IC card is in a standalone state is set to a first resonant frequency when the IC card starts operating. When the resonant frequency of the antenna unit is increased from the first resonant frequency to a second resonant frequency when the IC card is in a standalone state, the resonant frequency of the antenna unit deviates from the carrier frequency and the rectified output current decreases. However, because the resonant frequency is changed while a certain amount of surplus current is generated, the minimum voltage at which the IC card can operate can be maintained. When multiple IC cards are stacked, the resonant frequency of the antenna unit is lower than when an IC card is in a standalone state, so the resonant frequency at which the IC cards start operating when multiple IC cards are stacked is lower than the carrier frequency. When the resonant frequency of the antenna unit is increased from the first resonant frequency to the second resonant frequency when multiple IC cards are stacked, the resonant frequency of the antenna unit approaches the carrier frequency and the rectified output current increases, so the minimum voltage at which the IC cards can operate can be maintained.

[0181] As a result, whether the IC card is in a single state or in a state where multiple IC cards are stacked, the minimum voltage at which the IC card can operate can be maintained when the resonant frequency is corrected, thereby ensuring stable operation of the IC card.

[0182] (Technology 5) The present invention further includes a power supply unit that generates a predetermined power supply voltage to be applied to the load circuit unit from the rectified output current, and the resonant frequency variable circuit is a circuit for changing the resonant frequency of the antenna unit to at least a third resonant frequency and a fourth resonant frequency, the power supply unit includes a shunt power supply circuit that flows a shunt current to a ground reference potential in accordance with an input voltage to the power supply unit and the predetermined power supply voltage, and the detection unit includes a current detection circuit that outputs a detection current whose current value correlates with the current value of the shunt current, and compares the current value of the detection current with a first detection current threshold, or a comparator that compares the first detection current threshold with a second detection current threshold that is smaller than the first detection current threshold and outputs the comparison result as the detection signal, wherein the resonance frequency control unit controls the resonance frequency variable circuit to change the resonance frequency of the antenna unit to the fourth resonance frequency when the detection signal indicates that the current value of the detection current is greater than the first detection current threshold, and controls the resonance frequency variable circuit to change the resonance frequency of the antenna unit to the third resonance frequency when the detection signal indicates that the current value of the detection current is equal to or smaller than the second detection current threshold.

[0183] The shunt current is a current equivalent to the excess current, and the value of the detection current is correlated with the value of the excess current. The closer the distance between the IC card and the reader / writer, the larger the value of the detection current; in other words, the farther the distance between the IC card and the reader / writer, the smaller the value of the detection current. For example, suppose the resonant frequency of the antenna unit at the start of operation of the IC card in a standalone state is set to a third resonant frequency, and the third resonant frequency is set as the carrier frequency. Furthermore, suppose the first detection current threshold is set to a value corresponding to a sufficient excess current.

[0184] When an IC card is brought close to a reader / writer in a standalone state, the current value of the detection current gradually increases, and when it exceeds the first detection current threshold, the resonant frequency is raised to the fourth resonant frequency. As a result, the resonant frequency deviates from the carrier frequency and the excess current decreases, but even if the excess current decreases slightly from a state in which sufficient current is flowing, the minimum voltage at which the IC card can operate can be maintained. On the other hand, when an IC card is moved away from the reader / writer in a standalone state, the current value of the detection current gradually decreases, and when it falls below the second detection current threshold, the resonant frequency is lowered to the third resonant frequency. As a result, the resonant frequency approaches the carrier frequency and the excess current increases, so the minimum voltage at which the IC card can operate can be maintained.

[0185] When multiple IC cards are stacked, the resonant frequency of the antenna unit is lower than when each IC card is alone, so the resonant frequency of the IC cards when they start operating when multiple IC cards are stacked is lower than the carrier frequency. When multiple IC cards are stacked and brought closer to a reader / writer, the current value of the detection current gradually increases, and when it exceeds the first detection current threshold, the resonant frequency is raised. As a result, the resonant frequency approaches the carrier frequency and the excess current increases, so the minimum voltage at which the IC cards can operate can be maintained. On the other hand, when multiple IC cards are stacked and moved away from the reader / writer, the current value of the detection current gradually decreases, and when it falls below the second detection current threshold, the resonant frequency is lowered. As a result, the resonant frequency deviates from the carrier frequency and the excess current decreases, but because the second detection current threshold is lower than the first detection current threshold, the excess current decreases after the IC cards are moved farther away from the reader / writer than when the current value of the detection current is compared to the first detection current threshold. Therefore, when the IC card is moved away from the reader / writer, the communication distance between the IC card and the reader / writer can be increased.

[0186] (Technology 6) A non-contact communication device according to Technology 5, wherein the first detection current threshold is a value greater than the current value of the rectified output current when the resonant frequency of the antenna unit is the third resonant frequency minus the current value of the rectified output current when the resonant frequency of the antenna unit is the fourth resonant frequency.

[0187] In this way, by setting the first detection current threshold to a value greater than the difference in rectified output current resulting from the change from the third resonant frequency to the fourth resonant frequency, it is possible to prevent excess current from being generated due to the change in resonant frequency, that is, to prevent the IC card from being unable to maintain the minimum voltage at which it can operate.

[0188] (Technology 7) A non-contact communication device according to any one of technologies 1 to 6, comprising a receiving unit that receives data based on a signal obtained from the antenna unit, and the load circuit unit controls the execution and stop of an operation of the resonant frequency control unit to change the resonant frequency of the antenna unit in accordance with the data.

[0189] According to this, if the resonant frequency of the antenna part changes while the IC card is receiving data from a reader / writer, there is a risk that the data may not be received correctly, so the operation of changing the resonant frequency can be stopped while data is being received.

[0190] (Technology 8) The present invention further includes a power supply unit that generates a predetermined power supply voltage to be applied to the load circuit unit from the rectified output current, the power supply unit including a shunt power supply circuit that flows a shunt current to a ground reference potential in accordance with an input voltage to the power supply unit and the predetermined power supply voltage, the detection unit including a current detection circuit that outputs a detection current whose current value correlates with the current value of the shunt current, and a comparator that compares the current value of the detection current with a first detection current threshold and outputs the comparison result, the load circuit unit having at least a first state and a second state, The frequency variable circuit is a circuit for changing the resonant frequency of the antenna unit to at least a fifth resonant frequency and a sixth resonant frequency, and the first detection current threshold is greater than the sum of the current value of the rectified output current when the resonant frequency of the antenna unit is the fifth resonant frequency minus the current value of the rectified output current when the resonant frequency of the antenna unit is the sixth resonant frequency, and the value of the load current in the second state minus the load current in the first state.

[0191] According to this, when the IC card is in a state where data processing is being performed in the load circuit unit (second state), the load current is larger than when the IC card is in a state where data processing is not being performed in the load circuit unit (first state). Therefore, by setting the first detection current threshold taking into account the load current in the second state, it is possible to prevent excess current from being generated due to a change in the resonant frequency, that is, to prevent the IC card from being unable to maintain the minimum voltage at which it can operate.

[0192] (Technology 9) A non-contact communication device according to any one of technologies 1 to 8, comprising a receiving unit that receives data based on a signal obtained from the antenna unit, and the load circuit unit determines whether an ID indicated by the data matches an ID of the non-contact communication device, and if they do not match, executes an operation of the resonant frequency control unit to change the resonant frequency of the antenna unit regardless of the detection signal.

[0193] According to this, when the ID of the card itself matches the ID of the data, it is not possible to determine whether a single IC card or multiple IC cards are stacked, and the resonant frequency is changed according to the detection signal. On the other hand, when the ID of the card itself does not match the ID of the data, multiple IC cards are stacked (i.e., the resonant frequency is low), and the resonant frequency can be forcibly increased regardless of the detection signal, and the resonant frequency can be brought closer to the carrier frequency.

[0194] (Technology 10) A control method for a contactless communication device, the contactless communication device including: an antenna unit that receives power from a transmitting / receiving device via contactless communication; a resonant frequency variable circuit that changes the resonant frequency of the antenna unit; a rectifier unit that rectifies an antenna output current output from the antenna unit; a load circuit unit that consumes a load current; and a detector unit that detects an excess current that is the difference between the rectified output current output from the rectifier unit and the load current, the control method including the steps of: acquiring a detection signal indicating a detection result of the excess current output from the detector unit; and changing the resonant frequency of the antenna unit by controlling the resonant frequency variable circuit in accordance with the detection signal.

[0195] This provides a control method that can maintain the minimum voltage at which the IC card can operate when the resonant frequency is corrected, regardless of whether the IC card is in a single state or in a state where multiple IC cards are stacked, thereby ensuring stable operation of the IC card.

[0196] (Technology 11) A program for causing a computer to execute the control method described in Technology 10.

[0197] This allows a program to be provided that can maintain the minimum voltage at which the IC card can operate when the resonant frequency is corrected, regardless of whether the IC card is in a single state or in a state where multiple IC cards are stacked, thereby ensuring stable operation of the IC card.

[0198] 101 Reader / writer 102, 504 Transmitter 103, 503 Receiver 104, 112, 212, 501 Coil antenna 105, 113, 213 Resonant capacitance 111, 211 IC card 114, 214, 505 Rectifier 115, 215 Load circuit 500, 500a, 500b IC card 502, 511 Resonant frequency variable circuit 506 Power supply 507, 513 Detector 508, 514 Controller 509, 512, 515 Resonant frequency controller 510 Smoothing capacitor 520, 521, 522, 523, 524, 560 Capacitor element 525, 526, 527, 528, 556, 557, 561 Switch element 530, 531, 532, 533 Diode elements 540, 551 Constant voltage source 541, 552 Comparator 542, 550 P-type MOSFET 543, 544 Resistor element 553, 555 Constant current source 554 Current mirror

Claims

1. an antenna unit that receives power from a transmitting / receiving device through non-contact communication; a resonant frequency variable circuit for varying the resonant frequency of the antenna unit; a rectification unit that rectifies an antenna output current output from the antenna unit; a load circuit section that consumes a load current; a detection unit that detects an excess current that is a difference between a rectified output current output from the rectification unit and the load current; a resonance frequency control unit that changes the resonance frequency of the antenna unit by controlling the resonance frequency variable circuit in response to a detection signal that indicates a detection result of the surplus current output from the detection unit. Contactless communication device.

2. a power supply unit that generates a predetermined power supply voltage to be applied to the load circuit unit from the rectified output current; the power supply unit includes a shunt power supply circuit that flows a shunt current to a ground reference potential in accordance with an input voltage to the power supply unit and the predetermined power supply voltage; the detection unit includes a current detection circuit that outputs a detection current whose current value correlates with the current value of the shunt current, and a comparator that compares the current value of the detection current with a first detection current threshold and outputs the comparison result as the detection signal; The resonance frequency control unit When the detection signal indicates that the current value of the detection current is equal to or less than the first detection current threshold, the resonant frequency variable circuit is controlled to lower the resonant frequency of the antenna unit; When the detection signal indicates that the current value of the detection current is greater than the first detection current threshold, the resonant frequency variable circuit is controlled to increase the resonant frequency of the antenna unit. The non-contact communication device according to claim 1 .

3. The first detection current threshold is a value greater than the difference between the rectified output current before and after changing the resonant frequency of the antenna unit. The non-contact communication device according to claim 2.

4. the resonant frequency variable circuit is a circuit for changing the resonant frequency of the antenna unit to at least a first resonant frequency and a second resonant frequency, the second resonant frequency is higher than the first resonant frequency; In a state in which the non-contact communication device receives power solely between the transmitting / receiving device and the antenna unit, the rectified output current is larger when the resonant frequency of the antenna unit is the first resonant frequency than when the resonant frequency of the antenna unit is the second resonant frequency. The non-contact communication device according to claim 1 .

5. a power supply unit that generates a predetermined power supply voltage to be applied to the load circuit unit from the rectified output current; the resonant frequency variable circuit is a circuit for changing the resonant frequency of the antenna unit to at least a third resonant frequency and a fourth resonant frequency, the power supply unit includes a shunt power supply circuit that flows a shunt current to a ground reference potential in accordance with an input voltage to the power supply unit and the predetermined power supply voltage; the detection unit includes a current detection circuit that outputs a detection current whose current value correlates with the current value of the shunt current, and a comparator that compares the current value of the detection current with a first detection current threshold or compares the current value of the detection current with a second detection current threshold that is smaller than the first detection current threshold, and outputs the comparison result as the detection signal; The resonance frequency control unit When the detection signal indicates that the current value of the detection current is greater than the first detection current threshold, controlling the resonant frequency variable circuit to change the resonant frequency of the antenna unit to the fourth resonant frequency; When the detection signal indicates that the current value of the detection current is equal to or less than the second detection current threshold, the resonance frequency variable circuit is controlled to change the resonance frequency of the antenna unit to the third resonance frequency. The non-contact communication device according to claim 1 .

6. The first detection current threshold is a value greater than a value obtained by subtracting the current value of the rectified output current when the resonant frequency of the antenna unit is the fourth resonant frequency from the current value of the rectified output current when the resonant frequency of the antenna unit is the third resonant frequency. The non-contact communication device according to claim 5.

7. a receiving unit that receives data based on a signal obtained from the antenna unit, The load circuit section controls execution and stop of an operation of the resonance frequency control section to change the resonance frequency of the antenna section in accordance with the data. The non-contact communication device according to any one of claims 1 to 6.

8. a power supply unit that generates a predetermined power supply voltage to be applied to the load circuit unit from the rectified output current; the power supply unit includes a shunt power supply circuit that flows a shunt current to a ground reference potential in accordance with an input voltage to the power supply unit and the predetermined power supply voltage; the detection unit includes a current detection circuit that outputs a detection current whose current value correlates with the current value of the shunt current, and a comparator that compares the current value of the detection current with a first detection current threshold and outputs the comparison result; the load circuit section has at least a first state and a second state, the resonant frequency variable circuit is a circuit for changing the resonant frequency of the antenna unit to at least a fifth resonant frequency and a sixth resonant frequency, The first detection current threshold is greater than a value obtained by subtracting the current value of the rectified output current when the resonant frequency of the antenna unit is the sixth resonant frequency from the current value of the rectified output current when the resonant frequency of the antenna unit is the fifth resonant frequency, and adding the value obtained by subtracting the load current in the first state from the load current in the second state. The non-contact communication device according to any one of claims 1 to 6.

9. a receiving unit that receives data based on a signal obtained from the antenna unit, The load circuit unit determines whether the ID indicated by the data matches the ID of the non-contact communication device, and if they do not match, executes the operation of the resonance frequency control unit to change the resonance frequency of the antenna unit regardless of the detection signal. The non-contact communication device according to any one of claims 1 to 6.

10. A control method for a non-contact communication device, comprising: The non-contact communication device an antenna unit that receives power from a transmitting / receiving device through non-contact communication; a resonant frequency variable circuit for varying the resonant frequency of the antenna unit; a rectification unit that rectifies an antenna output current output from the antenna unit; a load circuit section that consumes a load current; a detection unit that detects an excess current that is a difference between a rectified output current output from the rectification unit and the load current, The control method includes: acquiring a detection signal indicating a detection result of the surplus current output from the detection unit; and changing the resonance frequency of the antenna unit by controlling the resonance frequency variable circuit in response to the detection signal. Control method.

11. A program for causing a computer to execute the control method according to claim 10.