HK1139764B - Transponder, interrogator, and communication device - Google Patents

Description

Transponder, interrogator, and communication device

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention comprises subject matter relating to japanese priority patent application JP 2008-142131 filed to the present patent office at 30.5.2008, the entire contents of which are incorporated herein by reference.

Technical Field

The present invention relates to a transponder and an interrogator, and particularly to a transponder and an interrogator that realize high-speed communication via electromagnetic waves.

Background

In the related art, a communication system constituted by an interrogator which stores and reads predetermined information and a responder which responds to a request command from such an interrogator is widely used. A system that performs communication via electromagnetic waves with such a communication system is called a contactless communication system. Such a contactless communication system is used with, for example, an automatic turnstile (automatic turnstile) or a room entrance/exit management system, and by such a contactless communication system, a reader/writer is generally used as an interrogator, and a contactless IC card or a contactless ID card is used as a transponder.

For the noncontact IC card, for example, the tuning frequency that can most efficiently receive electromagnetic wave energy from the reader/writer is generally fixed at 13.56 MHz. However, in the case where such a noncontact IC card is placed in a wallet accommodating a plurality of noncontact IC cards having different uses, the influence of mutual inductance between the other noncontact IC cards stored in the wallet by a reader/writer lying flat on the other cards causes the tuning frequency of the noncontact IC card to fall to a frequency of less than 13.56 MHz. Therefore, assuming that a plurality of noncontact IC cards are used while being stored in a wallet, a noncontact IC card has been proposed in which the tuning frequency is fixed to 13.56MHz by shifting the tuning frequency thereof to a higher frequency (see, for example, japanese unexamined patent application publication No. 2005-197890) (fig. 2).

However, as shown below, if the tuning frequency of the contactless IC card is fixed to 13.56MHz, the data transfer speed between the contactless IC card and the reader/writer can reach a higher speed.

Fig. 16 is a conceptual diagram showing a modulation wave at the time of low-speed and high-speed communication transmitted from a reader/writer according to the related art. The modulated waves 720 and 721 of the reader/writer are shown by solid lines and broken lines, respectively, and the horizontal axis shows the frequency and the vertical axis shows the electromagnetic wave intensity. Further, the carrier frequency is 13.56 MHz.

The modulated waves 720 and 721 of the reader/writer are frequency components of a data signal to be transmitted to the noncontact IC card, and these two modulated waves are generated on both sides due to the carrier frequency of the carrier wave to transport the data signal at the center. Further, the modulated waves 720 and 721 of the reader/writer are modulated waves at the time of low-speed communication and high-speed communication, respectively. The high-speed communication described here means communication in the case where the data transfer speed between the reader/writer and the noncontact IC card is 1600Kbps or more.

Therefore, with a higher data transfer speed between the reader/writer and the noncontact IC card, the frequency bandwidth of the modulation wave 721 of the reader/writer spreads to be further away from the carrier frequency than the modulation wave 720 of the reader/writer. Additionally, we can see that the peak level of the modulation wave 721 of the reader/writer is reduced only by the amount of the frequency bandwidth widening of the modulation wave. This is because the output level of the electromagnetic wave decreases according to the gain of the antenna when the wave moves farther from the carrier frequency due to the antenna characteristics of the reader/writer. Next, high-speed communication with a contactless IC card according to the related art will be briefly described.

Fig. 17 is a conceptual diagram illustrating frequency characteristics of an antenna on a contactless IC card according to the related art. Here, the carrier frequency is 13.56 MHz. Furthermore, the horizontal axis shows frequency and the vertical axis shows gain.

Fig. 17A is a conceptual diagram illustrating frequency characteristics of an antenna on a contactless type C card according to the related art at the time of reception. A relationship between a reception frequency characteristic 810 of a noncontact IC card according to the related art and a modulation wave 721 of a reader/writer at the time of high-speed communication as shown in fig. 16 is shown in fig. 17A, and the reception frequency characteristic 810 of the noncontact IC card is shown by a solid line and the modulation wave of the reader/writer is shown by a broken line.

The reception frequency characteristic 810 of the noncontact IC card is a frequency characteristic of an antenna of the noncontact IC card in the case of receiving an electromagnetic wave from a reader/writer, and the vertical axis shows a gain. Here, the frequency at which the gain of the reception frequency characteristic 810 is the largest is the tuning frequency, and the tuning frequency thereof is set to the same frequency as the carrier frequency.

In this case, the frequency bandwidth of the modulated wave 721 of the reader/writer at the time of high-speed communication is wider and the electromagnetic intensity of the modulated wave 721 thereof is lower than the reception frequency characteristic 810 of the noncontact IC card according to the related art, so that it is difficult to receive the modulated wave 721 with the noncontact IC card according to the related art. Therefore, as a method of enabling reception of a low-level modulation wave by a noncontact IC card, it is conceivable to increase the size of a circuit to improve data detection accuracy, but this also leads to an increase in power consumption. Therefore, with a contactless IC card having no power supply, it is difficult to increase the circuit size to increase the detection accuracy of the data signal from the reader/writer.

On the other hand, as shown in fig. 17B, when data can be received from the reader/writer, a modulated wave 821 at the time of high-speed communication from a contactless IC card having a transmission frequency characteristic 820 is transmitted to the reader/writer. In this case, the reader/writer has a power supply different from that of the noncontact IC card, and thus the data detection accuracy can be improved by increasing the circuit size, and the modulated wave 821 from the noncontact IC card can be received.

Therefore, in the case of performing high-speed communication between the reader/writer and the noncontact IC card, if the tuning frequency of the noncontact IC card is fixed to the carrier frequency as in the related art, it is difficult to receive data at the time of high-speed communication from the reader/writer with the noncontact IC card.

Disclosure of Invention

With the related art described above, it is possible to perform stable communication by fixing the tuning frequency and the carrier frequency of the contactless IC card so as to match them with each other. However, when the tuning frequency and the carrier frequency of the contactless IC card are fixed as in the related art, it becomes difficult to increase the data transfer speed between the contactless IC card and the reader/writer to a high speed. Therefore, with reference to the following diagram, a description will be given about a case where the tuning frequency of the noncontact IC card is shifted from the carrier frequency.

Fig. 18A and 18B are conceptual diagrams showing the frequency characteristics of the noncontact IC card in the case where the tuning frequency of the noncontact IC card is shifted from the carrier frequency. The carrier frequency is 13.56 MHz. Also, the horizontal axis shows frequency.

Fig. 18A shows a relationship between the reception frequency characteristic 811 of the noncontact IC card and the modulation wave 721 of the reader/writer at the time of high-speed communication as shown in fig. 16.

The reception frequency characteristic 811 of the noncontact IC card is a frequency characteristic of an antenna of the noncontact IC card in the case of receiving an electromagnetic wave from a reader/writer, and the vertical axis shows a gain. The tuning frequency of the reception frequency characteristic 811 is fixed to a frequency (f) higher than the carrier frequency_c) So that only the sidebands with the high frequency of the modulated wave 721 can be received. Therefore, only one sideband of the modulation wave 721 of the reader/writer is received by the contactless IC card, but the reception level of the sideband thereof becomes high by the antenna gain of the contactless IC card. Therefore, the contactless IC card can ensure sufficient energy to detect high-speed data at the time of high-speed communication from the reader/writer. Therefore, the noncontact IC card can detect high-speed data from the reader/writer by shifting the tuning frequency of the noncontact IC card from the carrier frequency.

However, in this case, even if data received with the noncontact IC card is processed and replied to the reader/writer at the same data transfer speed, no replied data signal is received. This is because when the tuning frequency of the contactless IC card is shifted from the carrier frequency, as shown in fig. 18B, the transmission frequency characteristic 821 of the contactless IC card also exhibits the same tuning frequency (f) as the reception frequency characteristic 811_c). Specifically, when a data signal for responding to a reader/writer is replied from the contactless IC card, the frequency component of the data signal thereof is only one sideband 822 of the modulation wave. In this case, the noncontact IC card tunes the antenna frequency (f) during transmission_c) Moving to the side of sideband 822 so that the electromagnetic intensity of sideband 822 becomes high. However, with the reader/writer, sufficient energy cannot be obtained with only one sideband 822, and thus, it is difficult to detect data from the contactless IC card.

Therefore, in the case of performing high-speed communication, if the tuning frequency of the noncontact IC card is changed from the carrier frequency and fixed, a problem arises in that response data cannot be received from the noncontact IC card.

The need for high speed communication between the transponder and the interrogator has been met.

According to an embodiment of the invention, for a transponder, comprising: an antenna circuit that performs communication with an interrogator that is a communication target via an electromagnetic wave, the antenna circuit being configured from a coil and a variable capacitance circuit that are connected in parallel with each other, wherein a tuning frequency of the antenna circuit is a first frequency; and a tuning frequency control circuit that switches a tuning frequency of the coil and the variable capacitance circuit, which are connected in parallel with each other, to a second frequency in a case where the electromagnetic wave is transmitted through the antenna circuit. This leads to the effect that, in the case of transmission of electromagnetic waves, the tuning frequency is switched from a first frequency to a second frequency.

When the data processing of the data received from the interrogator is finished, the tuning frequency control circuit may switch the tuning frequency to the second frequency before transmitting the electromagnetic wave through the antenna circuit. This results in the following effects: the tuning frequency is switched to a second frequency before the transmission of the electromagnetic wave. In this case, the tuning frequency control circuit may switch the tuning frequency to the first frequency after transmitting the data processing result to the interrogator via the antenna circuit. This results in the following effects: after transmitting the result of the data processing to the interrogator, the tuning frequency is switched to the first frequency.

In the case where the tuning frequency control circuit switches the tuning frequency to the second frequency before the electromagnetic wave is transmitted through the antenna circuit at the time of ending the data processing of the data transmitted from the interrogator, the tuning frequency control circuit may switch the tuning frequency to the first frequency in the case where a power supply voltage generated by an alternating-current voltage induced in the antenna circuit via the electromagnetic wave from the interrogator is lower than a predetermined voltage. This results in the following effects: the tuning frequency is switched to a first frequency in a case where a power supply voltage generated by an alternating voltage induced in the antenna circuit is lower than a predetermined voltage.

Further, the first frequency may be set to a frequency higher than a peak of a sideband with a high frequency among sidebands transmitted from the interrogator. This results in the following effects: the data signal from the interrogator can be easily received.

Further, the first frequency may be set to a frequency lower than a peak of a sideband having a low frequency among the sidebands transmitted from the interrogator. This results in the following effects: the data signal from the interrogator can be easily received.

Further, the tuning frequency control circuit may switch the tuning frequency to the second frequency by controlling the variable capacitance circuit. This results in the following effects: the tuning frequency is switched to a second frequency by changing the capacitance of the variable capacitance circuit.

Further, the variable capacitance circuit may include a first fixed capacitance element and a switch that are directly connected and a second fixed capacitance element that is connected in parallel to the first fixed capacitance element and the switch that are directly connected; wherein the tuning frequency control circuit can change the capacitance of the variable capacitance circuit and switch the tuning frequency to the second frequency by controlling the switch.

Further, the variable capacitance circuit may include a variable capacitance diode, wherein the tuning frequency control circuit may switch the tuning frequency to the second frequency by controlling a capacitance of the variable capacitance diode. This results in the following effects: the tuning frequency is switched to a second frequency by controlling the capacitance of the variable capacitance diode.

According to an embodiment of the present invention, an interrogator comprises: an antenna circuit configured by a coil and a variable capacitance circuit connected in parallel to each other to perform communication with a transponder as a communication object via electromagnetic waves; and a tuning frequency control circuit that switches the tuning frequency of the antenna circuit to a first frequency when the electromagnetic wave from the antenna circuit is transmitted, and switches the tuning frequency of the antenna circuit to a second frequency when the electromagnetic wave transmitted by the transponder is received. This results in the following effects: the tuning frequency is switched to a first frequency in case of transmitting the electromagnetic wave and to a second frequency in case of receiving the electromagnetic wave.

Further, the tuning frequency control circuit may switch the tuning frequency of the antenna circuit to the second frequency after transmitting the data to be transmitted to the transponder via the antenna circuit. This results in the following effects: the tuning frequency of the antenna circuit is switched to a second frequency after the data to be transmitted have been transmitted to the transponder. In this case, when the processing of the response data with respect to the data from the transponder is ended, the tuning frequency control circuit may switch the tuning frequency of the antenna circuit to the first frequency before transmitting the electromagnetic wave from the antenna circuit. This results in the following effects: after transmission of the electromagnetic wave from the antenna circuit, the tuning frequency is switched to the first frequency.

Further, the first frequency may be set to a frequency higher than a peak of a sideband having a high frequency among sidebands transmitted from the antenna circuit. This results in the following effects: the peak level of the sidebands with high frequencies is further increased.

Further, the first frequency may be set to a frequency lower than a peak of a sideband having a low frequency among sidebands transmitted from the antenna circuit. This results in the following effects: the peak level of the sidebands with high frequencies is further increased.

Further, the tuning frequency control circuit may switch the tuning frequency of the antenna circuit to the first frequency or the second frequency by controlling the variable capacitance circuit. This results in the following effects: the tuning frequency is switched to the first frequency or the second frequency by changing the capacitance of the variable capacitance circuit.

Further, the variable capacitance circuit includes a first fixed capacitance element and a switch that are directly connected and a second fixed capacitance element that is connected in parallel to the first fixed capacitance element and the switch that are directly connected; wherein the tuning frequency control circuit can change the capacitance of the variable capacitance circuit by controlling the switch and switch the tuning frequency of the antenna circuit to the first frequency or the second frequency. This results in the following effects: the tuning frequency is switched to the first frequency or the second frequency by controlling a switch of the variable capacitance circuit.

Further, the variable capacitance circuit includes a variable capacitance diode, wherein the tuning frequency control circuit switches the tuning frequency of the antenna circuit to the first frequency or the second frequency by controlling a capacitance of the variable capacitance diode. This results in the following effects: the tuning frequency is switched to the first frequency or the second frequency by controlling the capacitance of the variable capacitance diode.

According to an embodiment of the present invention, a communication apparatus includes: an antenna circuit configured by a coil and a variable capacitance circuit connected in parallel with each other, and performing communication with another communication apparatus as a communication target via electromagnetic waves; and a tuning frequency control circuit that switches the tuning frequency of the antenna circuit to a first frequency in a case where an electromagnetic wave from another communication device is received, and switches the tuning frequency of the antenna circuit to a second frequency in a case where an electromagnetic wave transmitted by the antenna circuit is transmitted. This results in the following effects: the tuning frequency is switched to a first frequency in case of receiving the electromagnetic wave and to a second frequency in case of transmitting the electromagnetic wave.

According to the above configuration, a good advantage can be obtained in that the communication speed between the interrogator and the responder can be performed at an increased speed.

Drawings

Fig. 1 is a conceptual diagram showing a configuration example of a noncontact IC card according to an embodiment of the present invention;

fig. 2 is a conceptual diagram showing a configuration example of a tuning frequency adjustment circuit of a first example of a noncontact IC card according to an embodiment of the present invention;

fig. 3 is a conceptual diagram showing a configuration example of a tuning frequency control circuit of a first example of a noncontact IC card according to an embodiment of the present invention;

fig. 4A and 4B are conceptual diagrams schematically illustrating frequency characteristics of the antenna in fig. 2 and 3;

fig. 5 is a conceptual diagram schematically showing the frequency characteristics of the antenna when receiving in the case of using a p-type transistor as the switch 213;

fig. 6 is a flowchart showing an example of a processing sequence of the tuning frequency control processing of the contactless IC card according to the embodiment of the present invention;

fig. 7 is a conceptual diagram showing a configuration example of a tuning frequency adjustment circuit of a second example of a noncontact IC card according to an embodiment of the present invention;

fig. 8 is a conceptual diagram showing a configuration example of a tuning frequency control circuit of a second example of a noncontact IC card according to an embodiment of the present invention;

fig. 9 is a conceptual diagram showing a configuration example of a reader/writer according to an embodiment of the present invention;

fig. 10 is a conceptual diagram showing a configuration example of a first example of a reader/writer according to an embodiment of the present invention;

fig. 11 is a conceptual diagram showing a configuration example of a tuning frequency control circuit of a first example of a reader/writer according to an embodiment of the present invention;

fig. 12A and 12B are conceptual diagrams schematically illustrating frequency characteristics of the antenna in fig. 10 and 11;

fig. 13 is a conceptual diagram schematically showing the frequency characteristics of the antenna when transmission is performed using a p-type transistor as the switch 513;

fig. 14 is a flowchart showing an example of a processing sequence of the tuning frequency control processing of the reader/writer according to the embodiment of the present invention;

fig. 15 is a conceptual diagram showing a configuration example of a tuning frequency adjustment circuit of a second example of a reader/writer according to the embodiment of the present invention;

fig. 16 is a conceptual diagram showing a modulation wave at the time of low-speed and high-speed communication transmitted from a reader/writer according to the related art;

fig. 17A and 17B are conceptual diagrams illustrating frequency characteristics of an antenna of a contactless IC card according to the related art; and

fig. 18A and 18B are conceptual diagrams illustrating frequency characteristics of the contactless IC card in a case where the tuning frequency of the contactless IC card is shifted from the carrier frequency.

Detailed Description

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 is a conceptual diagram showing a configuration example of a noncontact IC card according to an embodiment of the present invention. Here, it is assumed that the data transfer speeds between the noncontact IC card and the reader/writer are the same as each other and the speed is high speed, and for example, the data transfer speed is 1696 Kbps.

The noncontact IC card 100 performs communication with a reader/writer via electromagnetic waves, and has an antenna 110 and a tuning frequency control circuit 300. The antenna 110 receives electromagnetic waves from a reader/writer that can pass communication, and transmits electromagnetic waves to the reader/writer corresponding thereto. The antenna 110 is a tuned circuit including a coil 120 and a tuned frequency adjusting circuit 200 connected in parallel with each other. The frequency at which the electromagnetic wave from the antenna 110 has the highest intensity is a tuning frequency, and the tuning frequency thereof is determined by the capacitance of the coil 120 and the tuning frequency adjusting circuit 200 connected in parallel with each other.

The tuning frequency adjustment circuit 200 changes the capacitance based on a signal from the tuning frequency control circuit 300. The tuning frequency adjustment circuit 200 is configured to cause the tuning frequency of the antenna 110 to change as the capacitance of the tuning frequency adjustment circuit 200 changes.

The tuning frequency control circuit 300 switches the tuning frequency of the antenna 110 between when receiving the electromagnetic wave and when transmitting the electromagnetic wave by controlling the capacitance of the tuning frequency adjustment circuit 200. For example, the tuning frequency control circuit 300 receives data to be transmitted from a reader/writer, and when data processing of such data is ended, the tuning frequency control circuit 300 switches the tuning frequency of the antenna 110 before transmission of the electromagnetic wave to the transmission frequency for transmission. In order to stably receive a data signal from a noncontact IC card with a reader/writer, it is assumed that a transmission frequency matches a carrier frequency. Here, the carrier frequency is 13.56MHz, for example.

Further, when the result of processing data from the reader/writer as response data is transmitted to the reader/writer via the antenna 110, the tuning frequency control circuit 300 switches the tuning frequency of the antenna 110 to the reception frequency to receive the electromagnetic wave from the reader/writer. It is assumed that the reception frequency is a frequency at which one sideband of the modulation wave from the reader/writer can be received, for example, about 17.30 MHz. Note that the modulation wave referred to here is a frequency component generated by superimposing a carrier wave on data with a reader/writer and appears symmetrically on both sides of the carrier frequency. Frequency components that occur at frequencies below the carrier frequency are the lower sidebands and frequency components that occur at frequencies above the carrier frequency are the upper sidebands.

Further, in the case where the power supply voltage generated by the electromagnetic wave from the reader/writer is lower than a predetermined voltage, the tuning frequency control circuit 300 switches the tuning frequency of the antenna 110 to the reception frequency. For example, in a case where the distance from the reader/writer increases and the power supply voltage drops below a predetermined voltage in a case where the tuning frequency of the antenna 110 is switched to the transmission frequency and the response data is transmitted to the reader/writer, the tuning frequency control circuit 300 switches the tuning frequency of the antenna 110 to the reception frequency. Therefore, before the power supply voltage is generated by the electromagnetic wave from the reader/writer, a case can be configured so that data from the reader/writer can be easily received.

Therefore, by switching the tuning frequency of the antenna 110 between the time of transmission and the time of reception, the data transfer speed between the noncontact IC card 100 and the reader/writer can be made higher.

Next, a configuration example of the tuning frequency adjustment circuit 200 will be described with reference to the following diagram. Fig. 2 is a conceptual diagram showing a configuration example of a tuning frequency adjustment circuit 200 in the first example of the noncontact IC card 100 according to the embodiment of the present invention. The noncontact IC card 100 has a coil 120, a variable capacitance circuit 210, and a tuning frequency control circuit 300. Except for the variable capacitance circuit 210, the configuration thereof is the same as in fig. 1, and thus a description thereof will be omitted here.

The variable capacitance circuit 210 has fixed capacitance elements 211 and 212 and a switch 213. The variable capacitance circuit 210 changes the capacitance of the variable capacitance circuit 210 by switching the switch 213 to an on state or an off state based on a signal from the tuning frequency control circuit 300. For example, in the case of receiving data from a reader/writer, the tuning frequency control circuit 300 switches the switch 213 to a non-on state, thereby setting the tuning frequency determined by the coil 120 and the fixed capacitance element 211 as the reception frequency. On the other hand, in the case of transmitting the response data to the reader/writer, the tuning frequency control circuit 300 switches the switch 213 to the on state, thereby setting the tuning frequency determined by the combined capacitance of the coil 120 and the fixed capacitance elements 211 and 212 as the transmission frequency.

Note that in this case, the added fixed capacitance elements 211 and 212 become a combined capacitance, and the capacitance of the variable capacitance circuit 210 is very large at the time of transmission, so that the transmission frequency of the antenna 110 is lower than the reception frequency. The transmission frequency is set to the same frequency as the carrier frequency so that the reader/writer can receive the response data, and therefore, the reception frequency is set to a frequency higher than the carrier frequency so that the reception frequency is set to receive the upper sideband from the reader/writer.

Therefore, with the first example of the noncontact IC card according to the embodiment of the present invention, the capacitance of the variable capacitance circuit 210 is changed by using the fixed capacitance elements 211 and 212 and the switch 213. Thus, the tuning frequency of the antenna 110 can be switched between transmission and reception.

Next, a configuration example of the tuning frequency control circuit 300 will be described with reference to the following diagram. Fig. 3 is a diagram showing a configuration example of a tuning frequency control circuit 300 in the first example of the noncontact IC card 100 according to the embodiment of the present invention. With the configuration shown in fig. 3, here is shown an example of the configuration of the tuning frequency control circuit 300 and the n-type transistor 233 in place of the switch 213 in the variable capacitance circuit 210. The other configurations are the same as those shown in fig. 2, so a description thereof will be omitted here.

The variable capacitance circuit 210 has an n-type transistor 233 in place of the switch 213. The n-type transistor 233 functions as a switch such that the n-type transistor 233 is in a conductive state when an H (high) level potential is applied to its gate terminal, and the n-type transistor 233 is in a non-conductive state when an L (low) level potential is applied to its gate terminal.

The tuning frequency control circuit 300 has a data processing circuit 310, a power generation circuit 320, a capacitance control circuit 330, a resistor 340, and an n-type transistor 350.

The data processing circuit 310 performs data processing upon receiving data from the reader/writer via the antenna 110, and replies response data to the reader/writer via the antenna 110. When the data processing ends, the data processing circuit 310 outputs its end notification to the capacitance control circuit 330. Further, when the reply to the response data of the reader/writer ends, the data output circuit 310 outputs its reply end notification to the capacitance control circuit 330. Further, the data processing circuit 310 generates a response data signal having a predetermined data transfer speed (e.g., 1696 Kbps).

The power supply generation circuit 320 rectifies an ac voltage induced in the antenna 110 by an electromagnetic wave from the reader/writer to generate a dc voltage as a power supply voltage. The power supply generation circuit 320 supplies the generated power supply voltage to the data processing circuit 310, the capacitance control circuit 330, and the resistor 340.

The n-type transistor 350 functions as a switch so as to be in a conductive state when an H-level potential is applied to its gate terminal and in a non-conductive state when an L-level potential is applied to its gate terminal. Through the n-type transistor 350, a source terminal thereof is connected to one end of the resistor 340 and a gate terminal of the n-type transistor 233, and a drain terminal thereof is grounded.

When the n-type transistor 350 is in a conducting state, the resistor 340 lowers the power supply voltage supplied from the power supply generation circuit 320. In this case, 0V (volt) is supplied as an L level to the gate terminal of the n-type transistor 233. Note that when the n-type transistor 350 is in a non-conductive state, a current does not flow into the resistor 340, so that the power supply voltage supplied from the power supply generation circuit 320 is supplied to the gate terminal of the n-type transistor 233. Further, one end of the resistor 340 is connected to the source terminal of the n-type transistor 350 and the gate terminal of the n-type transistor 233, and the other end thereof is connected to the data processing circuit 310, the power supply generation circuit 320, and the capacitance control circuit 330.

The capacitance control circuit 330 applies an H-level or L-level potential to the gate terminal of the n-type transistor 350. For example, when the power supply potential is supplied from the power supply generation circuit 320, the capacitance control circuit 330 applies an H-level potential to the gate terminal of the n-type transistor 350. In this case, the n-type transistor 350 is turned on, and the gate of the n-type transistor 233 is at the L level, so that the n-type transistor 233 is not turned on. Accordingly, the tuning frequency control circuit 300 can cause the tuning frequency of the antenna 110 determined by the fixed capacitive element 211 and the coil 120 to be set as the reception frequency.

Further, when the notification of data processing output from the data processing circuit 310 ends, the capacitance control circuit 330 applies an L-level potential to the gate terminal of the n-type transistor 350. In this case, the n-type transistor 350 is off, and the power supply voltage is supplied as an H-level potential to the gate terminal of the n-type transistor 233, so that the n-type transistor 233 is turned on. Accordingly, the tuning frequency control circuit 300 may cause the tuning frequency of the antenna 110 determined by the combined capacitance of the fixed capacitance elements 211 and 212 and the coil 120 to be set as the transmission frequency.

Further, when a reply end notification to the response data is output from the data processing circuit 310, the capacitance control circuit 330 applies an H-level potential to the gate terminal of the n-type transistor 350. In this case, the n-type transistor 350 is turned on, and the gate terminal of the n-type transistor 233 is at the L level, so that the n-type transistor 233 is non-conductive. Accordingly, the tuning frequency control circuit 300 can cause the tuning frequency of the antenna 110 determined by the fixed capacitance element 211 and the coil to be set as the reception frequency.

Therefore, if the distance between the noncontact IC card 100 and the reader/writer is a certain distance, the power supply voltage is lower than the moving voltage of the noncontact IC card. In this case, the n-type transistor 233 is non-conductive, and the tuning frequency of the antenna 110 is set to the reception frequency determined by the fixed capacitive element 211 and the coil 120. Therefore, if communication between the noncontact IC card 100 and the reader/writer is restarted, the tuning frequency of the antenna 110 is set to the reception frequency, so that the tuning frequency control circuit 300 can receive data from the reader/writer.

Next, the frequency characteristics of the antenna 110 will be described with reference to the following diagrams. Fig. 4A and 4B are conceptual diagrams schematically illustrating frequency characteristics of the antenna 110 in fig. 2 and 3. Here, the carrier frequency is 13.56 MHz. Further, the horizontal axis is shown as frequency.

Fig. 4A is a conceptual diagram illustrating frequency characteristics of the antenna 110 at the time of reception. Here, the relationship between the reception frequency characteristic 250 of the noncontact IC card and the modulation wave 661 of the reader/writer is shown, and the reception frequency characteristic 250 of the noncontact IC card is shown by a solid line, and the modulation wave 661 of the reader/writer is shown by a broken line.

The modulation wave 661 of the reader/writer is a frequency component of the data signal from the reader/writer, and is generated symmetrically on both sides of the carrier frequency. Frequency components that occur at frequencies below the carrier frequency are the lower sidebands, while frequency components that occur at frequencies above the carrier frequency are the upper sidebands.

The reception frequency characteristic 250 of the noncontact IC card is a frequency characteristic of the antenna 110 at the time of reception, and the vertical axis is shown as a gain. The contactless IC card has the highest reception frequency characteristic 250Frequency (f) of gain_cr1) To tune a frequency, and to tune a frequency (f)_cr1) Is the receive frequency. The reception frequency characteristic 250 of the noncontact IC card is set to be able to stably receive the upper sideband of the modulated wave 661, thereby setting the reception frequency (f)_cr1) Is set to a frequency at least higher than the peak of the upper sideband. This is because the frequency component higher than the peak of the upper sideband is equal to the high frequency component of the data signal, so that the frequency component higher than the peak of the upper sideband can be received more stably, and thus the data signal can be detected more stably. However, if the frequency (f) is received_cr1) Frequencies that are too high above the peak of the upper band receive no energy from the carrier. Therefore, the reception frequency is set in view of this situation. Therefore, by setting the reception frequency higher than that of the upper sideband, a high-speed data signal can be received from the reader/writer.

Note that the peak frequency of the upper/lower sidebands changes depending on the continuous bit value of the data signal, but here we assume the case where the peak of the upper/lower sidebands is farthest from the carrier frequency. For example, if we assume a transmission method in which a data signal that has been manchester-encoded is subjected to amplification modulation, this applies when a bit of the data signal occurs randomly, in the case where the peak of the upper/lower sidebands is farthest from the carrier frequency. The distance of the peak of the upper/lower sidebands from the carrier frequency at this time is only the frequency of the clock signal that generates the data transfer speed. Therefore, for example, if the frequency of the clock signal generating the data transfer speed is 1.696MHz, the peak frequency of the upper/lower sidebands is 15.256(═ 13.560+1.696) MHz, and thus, the reception frequency (f) will be received_cr1) Is set to a frequency at least higher than 15.256 MHz.

Fig. 4B is a conceptual diagram illustrating frequency characteristics of the antenna 110 at the time of transmission. Here, the relationship between the transmission frequency characteristic 260 of the noncontact IC card and the modulation wave 361 of the reader/writer is shown, and the transmission frequency characteristic 260 of the noncontact IC card is shown by a solid line and the modulation wave 361 of the reader/writer is shown by a broken line. The transmission frequency characteristic 260 of the noncontact IC card is a frequency characteristic in the case of transmitting an electromagnetic wave from the antenna 110 and the vertical axis shows a gain. The transmission frequency, which is the tuning frequency of the transmission frequency characteristic 260 of the contactless IC card, is set to the same frequency as the carrier frequency.

Therefore, by setting the transmission frequency to the same frequency as the carrier frequency, the modulated wave generated by the data signal of the noncontact IC card 100 can be received with the reader/writer.

Note that, with the first example of the contactless IC card 100 according to the embodiment of the present invention, a description is given with respect to an example in which the reception frequency of the antenna 110 is set so that the upper sideband can be received more stably, but setting that the lower sideband can be received more stably can be performed. In this case, this can be achieved by using a p-type transistor operating opposite to the n-type transistor 233 instead of the n-type transistor 233 as the switch 213. The p-type transistor is a switch that enters a non-conductive state when an H-level potential is applied to its gate terminal and enters a conductive state when an L-level potential is applied. For example, when an electromagnetic wave is received from a reader/writer, an H-level potential is applied from the capacitance control circuit 330 to the gate terminal of the n-type transistor 350, the potential of the gate terminal of the p-type transistor is L-level, and the p-type transistor is turned on. Therefore, the reception frequency of the antenna 110 is determined by the combined capacitance of the fixed capacitance elements 211 and 212 and the coil 120.

Further, in the case of transmitting response data to the reader/writer, an L-level potential is applied to the gate terminal of the n-type transistor 350 through the capacitance control circuit 330, so that the gate terminal potential of the p-type transistor is H-level, and the p-type transistor is non-conductive. Therefore, the transmission frequency of the antenna 110 is determined by the fixed capacitive element 211 and the coil 120. Therefore, the reception frequency of the antenna 110 can be set to a frequency lower than the transmission frequency. The transmission frequency is set to the same frequency as the carrier frequency so that response data can be received with the reader/writer. Therefore, the reception frequency is set so that the lower sideband of a frequency lower than the carrier frequency can be received more stably.

Fig. 5 is a diagram schematically showing the antenna 110 receiving in the case of using a p-type transistor as the switch 213Conceptual diagram of frequency characteristics of time. Here, the carrier frequency is shown as 13.56 MHz. Furthermore, the horizontal axis is shown as frequency. Note that the modulation wave 661 of the reader/writer is the same as that shown in fig. 4A. In addition, the frequency characteristics of the antenna 110 at the time of transmission are the same as those shown in fig. 4B, so a description thereof will be omitted here. The reception frequency characteristic 251 is shown by a solid line and the modulation wave 661 of the reader/writer is shown by a broken line. The reception frequency characteristic 251 is a frequency characteristic at the time of reception with the antenna 110, and the vertical axis shows a gain. The highest gain (f) in the reception frequency characteristic 251_cr2) The frequency of (1) is a reception frequency.

In this case, the reception frequency characteristic 251 is set so that the lower sideband of the modulated wave 661 can be received more stably. When receiving the lower sideband, the receiving frequency (f)_cr2) Is set to a frequency opposite the upper sideband below the peak of the lower sideband. Thus, the data signal can be detected more stably as described above.

Therefore, as a modified example of the first embodiment, the reception frequency is set to a frequency lower than the peak value of the lower sideband by using the p-type transistor as the switch 213, so that a high-speed data signal can be received from the reader/writer.

Next, the operation of the noncontact IC card 100 according to the embodiment of the present invention will be described with reference to the drawings. Fig. 6 is a flowchart showing an example of a processing sequence of the tuning frequency control processing of the noncontact IC card 100 according to the embodiment of the present invention.

First, the flow waits until an electromagnetic wave from the reader/writer is detected (step S911). Next, the electromagnetic wave is received and power is supplied through the power supply generation circuit, and data is received from the reader/writer (step S912). Then, a CRC value of the received data is calculated (step S913). By confirming the CRC value, it is determined whether there is any error in the received data (step S914). In the case where there is an error in the received data, the flow returns to step S911.

On the other hand, if there is no error in the received data, data processing of such data is performed (step S915). Next, when the data processing is ended, the tuning frequency of the antenna 110 is switched to the transmission frequency to transmit the electromagnetic wave (step S916). Next, response data as a result of the data processing of the received data is transmitted to the reader/writer (step S917). Next, when the response data is transmitted, the tuning frequency is switched to the reception frequency (step S918), and the flow returns to step S911.

Therefore, each time data is received from the reader/writer, communication is performed by switching the tuning frequency to the transmission frequency before transmitting response data to the reader/writer, and switching to the reception frequency when transmitting its response data, and these operations are repeated until a series of communication ends.

Therefore, with the first example of the noncontact IC card 100 according to the embodiment of the present invention, by using the fixed capacitance elements 211 and 212 and the switch 213, the capacitance of the variable capacitance circuit 210 can be changed and the tuning frequency of the antenna 110 can be switched between at the time of transmission and at the time of reception.

Fig. 7 is a conceptual diagram showing a configuration example of the tuning frequency adjustment circuit 200 in the second example of the noncontact IC card 100 according to the embodiment of the present invention. The configuration of the noncontact IC card 100 shown in fig. 7 has a variable capacitance diode 220 instead of the variable capacitance circuit 210 serving as the tuning frequency adjustment circuit 200. Note that the configuration is the same as that shown in fig. 1 except for the variable capacitance diode 220, so description will be omitted here.

The variable capacitance diode 220 is capable of varying capacitance according to a voltage applied through the tuning frequency control circuit 300.

Therefore, by using the variable capacitance diode 220, the capacitance of the variable capacitance diode 220 is changed and the tuning frequency of the antenna 110 is switched between at the time of transmission and at the time of reception.

Fig. 8 is a diagram showing a configuration example of the tuning frequency control circuit 300 in the second example of the noncontact IC card 100 according to the embodiment of the present invention. Instead of the resistor 340 shown in fig. 3, resistors 341 and 342 are shown here. Further, instead of the variable capacitance circuit 210, a variable capacitance diode 220 is shown.

The tuning frequency control circuit 300 has a data processing circuit 310, a power supply generation circuit 320, a capacitance control circuit 330, resistors 341 and 342, and an n-type transistor 350. The tuning frequency control circuit 300 is the same as that shown in fig. 3 except for the resistors 341 and 342, so description will be omitted herein.

The resistor (R1)341 and the resistor (R2)342 are based on the power supply voltage (V) supplied from the power supply generation circuit 320_CC) Two different potentials are provided to the variable capacitance diode 220. For example, in the case where the n-type transistor 350 is in a non-conductive state, a potential (Vcc · (R2/(R1+ R2))) divided by the resistors 341 and 342 is supplied as an H level. Further, in the case where the n-type transistor 350 is in a turned-on state, a current flows into the n-type transistor 350 via the resistor 341, thereby supplying a potential of 0V (volt) as an L level to the variable capacitance diode 220.

Therefore, the capacitance of the variable capacitance diode 220 is changed by changing the potential applied to the variable capacitance diode 220 using the resistors 341 and 342 and the n-type diode 350. Therefore, as shown in fig. 4, the tuning frequency of the antenna 110 is switched to the reception frequency (f)_cr1) To receive the upper sideband at reception and switch to the same transmission frequency as the carrier frequency at transmission. Further, as shown in fig. 5, by inverting the characteristic of the variable capacitance diode 220, the tuning frequency of the antenna 110 can be switched to a reception frequency (f) at which the lower sideband can be stably received from the reader/writer at the time of reception_cr2). Further, at the time of transmission, the tuning frequency of the antenna 110 may be switched to a transmission frequency of the same frequency as the carrier frequency.

Further, with the second example of the noncontact IC card 100 according to the embodiment of the present invention, the number of configuration elements for switching the tuning frequency can be reduced as compared with the first example, and thus, the circuit size can be suppressed.

As described above, with the noncontact IC card 100, the capacitance of the tuning frequency adjustment circuit 200 is changed in accordance with the reception and transmission of electromagnetic waves by the tuning frequency control circuit 300, so that the tuning frequency of the antenna 110 can be switched to the reception frequency or the transmission frequency of electromagnetic waves. An example of switching the tuning frequency of the noncontact IC card 100 at the time of transmission and reception of electromagnetic waves is described, thereby realizing high-speed communication between the noncontact IC card and the reader/writer, but this is similarly applicable to the reader/writer.

Now, an application example of the reader/writer will be described with reference to the following diagram. Fig. 9 is a conceptual diagram illustrating a configuration example of a reader/writer according to an embodiment of the present invention. We assume that the data transfer speeds between the noncontact IC card and the reader/writer are the same as each other and are high speeds, and for example, we assume that the data transfer speed thereof is 1696 Kbps. Further, it is assumed that the tuning frequency of the noncontact IC card is not switched at the time of data transmission and at the time of reception, but is fixed at the same frequency as the carrier frequency.

The reader/writer 400 performs communication with a contactless IC card via electromagnetic waves, and has an antenna 410 and a tuning frequency control circuit 600. The antenna 410 generates electromagnetic waves and transmits data to be transmitted to a noncontact IC card to be subjected to communication, and receives electromagnetic waves from the noncontact IC card. The antenna 410 is a tuned circuit composed of a coil 420 and a tuned frequency adjusting circuit 500. The frequency having the highest electromagnetic intensity from the antenna 410 is a tuning frequency, and the tuning frequency thereof is determined by the capacitance of the coil 420 and the tuning frequency adjusting circuit 500 connected in parallel to each other.

The tuning frequency adjustment circuit 500 changes the capacitance based on a signal from the tuning frequency control circuit 600. The tuning frequency adjustment circuit 500 is configured to cause the tuning frequency of the antenna 410 to change as the capacitance of the tuning frequency adjustment circuit 500 changes.

The tuning frequency control circuit 600 switches the tuning frequency of the antenna 410 between the time of transmission and the time of receiving data for communication by controlling the capacitance of the tuning frequency adjustment circuit 500. Specifically, when an electromagnetic wave is transmitted, the tuning frequency control circuit 600 switches the tuning frequency of the antenna 410 to a transmission frequency for transmission. We assume that the transmission frequency is a frequency in which only one sideband of the modulation wave from the reader/writer 400 is a high frequency (for example, about 17.30MHz) to enable stable reception of the data signal from the reader/writer 400 with the noncontact IC card.

Further, when transmitting data to the contactless IC card via the antenna 410, the tuning frequency control circuit 600 switches the tuning frequency of the antenna 410 to a reception frequency for receiving response data from the contactless IC card. It is assumed that the reception frequency is the same as the carrier frequency so that response data can be stably received from the contactless IC card. The carrier frequency here is 13.56MHz, for example.

Further, when processing response data from the contactless IC card, the tuning frequency control circuit 600 switches the tuning frequency of the antenna 410 to the transmission frequency in order to transmit data to the contactless IC card.

Therefore, by switching the tuning frequency of the antenna 410 at the time of transmission and at the time of reception, the data transfer speed between the reader/writer 400 and the noncontact IC card can be increased.

Next, a configuration example of the tuning frequency adjustment circuit 500 will be described with reference to the drawings. Fig. 10 is a conceptual diagram showing a configuration example of a first example of the reader/writer 400 according to the embodiment of the present invention. The reader/writer 400 has a coil 420, a variable capacitance circuit 510, and a tuning frequency control circuit 600.

The variable capacitance circuit 510 has fixed capacitance elements 511 and 512 and a switch 513.

The variable capacitance circuit 510 changes the capacitance of the variable capacitance circuit 510 by placing the switch 513 in an on state or an off state based on a signal from the tuning frequency control circuit 600. For example, in the case of transmitting data to be transmitted to the contactless IC card via the antenna 410, the tuning frequency control circuit 600 sets the tuning frequency determined by the coil 420 and the fixed capacitance element 511 as the transmission frequency by switching the switch 513 to the non-on state. On the other hand, in the case of receiving response data from the noncontact IC card, the tuning frequency control circuit 600 sets a tuning frequency determined by the combined capacitance of the coil 420 and the fixed capacitance elements 511 and 512 as a reception frequency by the switch 513 being turned on.

Therefore, the capacitance of the variable capacitance circuit 510 is changed by using the fixed capacitance elements 511 and 512 and the switch 513. Therefore, the tuning frequency of the antenna 110 can be switched between transmission and reception.

Next, a configuration example of the tuning frequency control circuit 600 will be described with reference to the following diagram. Fig. 11 is a diagram showing a configuration example of the tuning frequency control circuit 600 of the first example of the reader/writer 400 according to the embodiment of the present invention. With the configuration shown in fig. 11, an example of the configuration of the tuning frequency control circuit 600 and the n-type transistor 533 in place of the switch 513 in the variable capacitance circuit 510 is shown. The remaining configuration is the same as that shown in fig. 10, so description will be omitted herein.

The variable capacitance circuit 510 has an n-type transistor 533 instead of the switch 513. The n-type transistor 533 is a switch which is turned on when an H-level potential is applied to its gate terminal and is turned off when an L-level potential is applied to its gate terminal.

The tuning frequency control circuit 600 has a carrier generation circuit 610, a multiplier 620, an amplifier 630, a data processing circuit 640, and a capacitance control circuit 650. The carrier generation circuit 610 generates a carrier signal for carrying data as information to be transmitted to the noncontact IC card. The carrier generation circuit 610 supplies the carrier signal to the multiplier 620.

The multiplier 620 subjects the carrier signal among the data signals generated by the data processing circuit 640 to amplification modulation. The multiplier 620 supplies the amplified modulated wave subjected to the amplification modulation to the amplifier 630. The amplifier 630 amplifies the amplified modulation wave generated by the multiplier 620 and transmits it to the contactless IC card via the antenna 410.

The data processing circuit 640 encodes information to be transmitted to the noncontact IC card at a predetermined data transmission speed, and generates a data signal. For example, the data processing circuit 640 generates a data signal having a data transfer speed of 1696Kbps by Manchester (Manchester) encoding. Further, the data processing circuit 640 receives response data from the contactless IC card via the antenna 410, and processes the response data thereof. Further, the data processing circuit 640 outputs a data transmission notification to the capacitance control circuit 650 before generating and transmitting a data signal to the noncontact IC card. Further, when the data signal is transmitted to the noncontact IC card via the antenna 410, the data processing circuit 640 outputs a transmission end notification to the capacitance control circuit 650.

The capacitance control circuit 650 applies an H-level or L-level potential to the gate terminal of the n-type transistor 533. For example, if power is supplied to the reader/writer 400 itself and electromagnetic waves are generated, the capacitance control circuit 650 applies an L-level potential to the gate terminal of the n-type transistor 533. In this case, the n-type transistor 533 is non-conductive, and the tuning frequency control circuit 600 sets the tuning frequency of the antenna 410 determined by the fixed capacitance element 511 and the coil 420 as the transmission frequency.

Further, when the transmission end notification is output from the data processing circuit 640, the capacitance control circuit 650 applies an H-level potential to the gate terminal of the n-type transistor 533. In this case, the n-type transistor 533 is turned on, and the tuning frequency control circuit 600 sets the tuning frequency of the antenna 410 determined by the combined capacitance of the fixed capacitance elements 511 and 512 and the coil 420 as the reception frequency.

Further, when response data is received from the contactless IC card, the processing of the response data thereof is ended, and a data transmission notification is output, the capacitance control circuit 650 applies an L-level potential to the n-type transistor 533. In this case, the n-type transistor 533 is non-conductive, and the tuning frequency control circuit 600 sets the tuning frequency of the antenna 410 determined by the fixed capacitance element 511 and the coil 420 as the transmission frequency.

Therefore, by changing the capacitance of the variable capacitance circuit 510, the tuning frequency of the antenna 410 can be switched between when the electromagnetic wave is transmitted and when it is received.

Next, the frequency characteristics of the antenna 410 will be described with reference to the following diagrams. Fig. 12A and 12B are conceptual diagrams schematically illustrating frequency characteristics of the antenna 410 in fig. 10 and 11. The carrier frequency is assumed to be 13.56 MHz. Furthermore, the horizontal axis is shown as frequency. Note that it is assumed here that the antenna tuning frequency is fixedly set to the carrier frequency at the time of transmission and reception of the contactless IC card.

Fig. 12A is a conceptual diagram illustrating frequency characteristics of the antenna 410 at the time of reception. The relationship among the reception frequency characteristic 270 of the noncontact IC card, the transmission frequency characteristic 560 of the reader/writer, the upper sideband 662 of the reader/writer, and the modulation wave 721 of the reader/writer according to the related art is shown in the figure.

The reception frequency characteristic 270 of the noncontact IC card is a frequency characteristic of the antenna when the noncontact IC card is received, and the vertical axis shows a gain.

A modulated wave 721 shown by a broken line, which is a modulated wave component from the reader/writer according to the related art, with the modulated wave of the antenna set to the carrier frequency, and the vertical axis shows the electromagnetic wave intensity. Note that the lower sideband will be omitted here for simplicity.

The transmission frequency characteristic 560 of the reader/writer shown by the dotted line is a frequency characteristic of the antenna 410 at the time of transmission, and the vertical axis shows the gain. The frequency (f) having the highest gain in the transmission frequency characteristic 560 of the reader/writer_rt1) To tune a frequency, and in this case the frequency (f)_rt1) Is the transmission frequency. The tuning frequency of the transmission frequency characteristic 560 of the reader/writer is the transmission frequency (f)_rt1) Is set to be at least higher than the frequency of the modulated wave 721 to raise the transmission level of the modulated wave 721.

The upper band 662 of the reader shown with a solid line is the frequency component of the data signal from the antenna 410 with the transmission frequency characteristic 560 of the reader. The upper sideband 662 of the reader/writer increases in electromagnetic wave intensity as compared with the modulated wave 721 according to the related art. Therefore, the upper sideband 662 from the reader/writer 400 is received by the noncontact IC card, so that sufficient energy can be secured to detect the data of the reader/writer 400.

Therefore, by setting the transmission frequency of the tuning frequency to a frequency higher than the peak value of the upper band, a high-speed data signal from the reader/writer 400 can be received with the noncontact IC card.

Note that the peak frequency of the upper sideband changes according to the continuous bit values of the data signal, but we assume the case where the peak frequency of the upper sideband is at most higher than the carrier frequency. For example, if a transmission method in which a manchester-encoded data signal is subjected to amplification modulation is assumed, this applies to the case where data signal bits are randomly generated in the case where the peak frequency of the upper sideband is higher than the carrier frequency at maximum. The peak of the upper sideband is now only a distance from the carrier frequency by the amount of the frequency of the clock signal that generates the data transfer rate. Therefore, if the frequency of the clock signal generating the data transfer speed is 1.696MHz, the peak frequency of the upper sideband is 15.256(═ 13.560+1.696) MHz, so that the transmission frequency (f) will be transmitted_rt1) Is set to a frequency at least higher than 15.256 MHz.

Fig. 12B is a conceptual diagram illustrating frequency characteristics of the antenna 410 at the time of transmission. The modulated wave 361 of the contactless IC card is shown by a dotted line and the reception frequency characteristic 550 of the reader/writer is shown by a solid line.

The reception frequency characteristic 550 of the reader/writer is a frequency characteristic of the antenna 410 when receiving an electromagnetic wave from the noncontact IC card, and the vertical axis is shown as a gain. Herein, the tuning frequency of the reception frequency characteristic 550 of the reader/writer is set to the same frequency as the carrier frequency. Note that the tuning frequency at this time is referred to as a reception frequency. Therefore, by setting the reception frequency to the same frequency as the carrier frequency, the reader/writer 400 can receive the modulated wave from the noncontact IC card.

Note that, with the first example of the reader/writer 400 according to the embodiment of the present invention, a description will be given of an example in which the reception frequency of the antenna 410 is set so that the electromagnetic intensity of the upper sideband is high, but setting may be performed so that the electromagnetic intensity of the lower sideband is high. This may be achieved by using a p-type transistor having an operation opposite to that of the n-type transistor instead of the switch 513 shown in fig. 10. The P-type transistor is a switch which is non-conductive when an H-level potential is applied to the gate terminal and is conductive when an L-level potential is applied to the gate terminal. In this case, when an electromagnetic wave is generated from the reader/writer 400, an L-level potential is applied to the gate terminal of the p-type transistor with the capacitance control circuit 650, and the transmission frequency is determined by the combined capacitance of the fixed capacitance elements 511 and 512 and the coil 420.

Therefore, when transmission of data to be transmitted to the noncontact IC card is ended, an H-level potential is applied to the gate terminal of the p-type transistor with the capacitance control circuit 650, the p-type transistor is non-conductive, and the reception frequency is determined by the fixed capacitance element 511 and the coil 420.

Accordingly, the transmission frequency of the antenna 410 may be set to a frequency lower than the reception frequency. The reception frequency of the antenna 410 is set to the same frequency as the carrier frequency so that the reader/writer can receive the response data. Therefore, the transmission frequency is set so that the electromagnetic intensity of the lower sideband of the reader/writer is high.

Fig. 13 is a conceptual diagram schematically showing the frequency characteristics of the antenna 410 at the time of transmission in the case of using a p-type transistor as the switch 513. Here, the carrier frequency is 13.56 MHz. Further, the horizontal axis shows frequency. The frequency characteristics of the antenna 410 at the time of reception are the same as those shown in fig. 12B, so a description thereof will be omitted. A relationship between the transmission frequency characteristic 561 of the reader/writer, the lower sideband 663 of the reader/writer, and the modulated wave 721 of the reader/writer according to the related art is shown.

A modulated wave 721 of the reader/writer according to the related art shown by a dotted line is a modulated wave component from the reader/writer with the tuning frequency of the antenna set to the carrier frequency, and the vertical axis shows the electromagnetic intensity. Note that the upper sideband is omitted for simplicity.

Is shown by a dotted lineThe transmission frequency characteristic 561 of the reader/writer is a frequency characteristic in the case where an electromagnetic wave is transmitted from the antenna 410, and the vertical axis shows a gain. The frequency (f) having the highest gain in the transmission frequency characteristic 561 of the reader/writer_rt2) Is the transmission frequency of the tuning frequency. In order to increase the transmission level of the modulated wave 721, the transmission frequency characteristic 561 of the reader/writer in this document is to transmit the frequency (f)_rt2) Is set to a frequency at least higher than the peak value of the modulation wave 721.

The lower sideband 663 of the reader-writer, shown with a solid line, is the frequency component of the data signal from the antenna 410 with the transmission frequency characteristic 561 of the reader-writer. The lower sideband 663 of the reader/writer has a higher electromagnetic intensity than the modulated wave 721 according to the related art. Therefore, the lower sideband 663 from the reader/writer 400 is received by the noncontact IC card, so that sufficient energy can be confirmed to detect the data of the reader/writer 400.

Next, the operation of the reader/writer 400 according to the embodiment of the present invention will be described with reference to the drawings. Fig. 14 is a flowchart showing an example of a processing sequence of the tuning frequency control process of the reader/writer 400 according to the embodiment of the present invention.

First, power is supplied to the reader/writer 400 itself (step S921). Next, the tuning frequency of the antenna 410 is switched to the transmission frequency by the tuning frequency control circuit 600 (step S922). Next, data to be transmitted to the contactless IC card is transmitted via the antenna 410 (step S923). When the transmission of the data signal is ended, the tuning frequency of the antenna 410 is switched to the reception frequency by the tuning frequency control circuit 600 (step S924). Next, the flow waits until the response data is replied from the contactless IC card, and in a case where the reply is not transmitted even after a predetermined amount of time has elapsed (step S925), the flow returns to step S922, and the tuning frequency of the antenna 410 is switched to the transmission frequency.

On the other hand, in the case of receiving the response data from the contactless IC card (step S925), the CRC value of the response data is calculated by the data processing circuit 640 (step S926). Next, it is determined whether there is any error in the received response data by confirming the CRC value (step S927). If there is no error in the received response data, data processing of the response data thereof is performed (step S928), and when the data processing ends, the flow returns to step S922, and the tuning frequency of the antenna 410 is switched to the transmission frequency.

Accordingly, the tuning frequency of the antenna 410 is switched to the transmission frequency and data is transmitted each time data to be transmitted to the contactless IC card is transmitted, and when the transmission thereof is ended, the tuning frequency is switched to the reception frequency to receive response data. The operations herein are repeated until the series of communications is completed.

Therefore, with the first example of the reader/writer 400 according to the embodiment of the present invention, by using the fixed capacitance elements 511 and 512 and the switch 513, the capacitance of the variable capacitance circuit 510 can be changed and the tuning frequency of the antenna 410 can be switched at the time of transmission and at the time of reception.

Fig. 15 is a diagram showing a configuration example of the tuning frequency adjustment circuit 500 of the second example of the reader/writer 400 according to the embodiment of the present invention. The configuration of the reader/writer 400 shown in fig. 15 has a variable capacitance diode 520 in place of the variable capacitance circuit 510 as the tuning frequency adjustment circuit 500. Note that the configuration is the same as that in fig. 11 except for the variable capacitance diode 520, so a description thereof will be omitted.

The variable capacitance diode 520 varies capacitance according to a voltage applied by the capacitance control circuit 650.

Thus, by using the variable capacitance diode 520, it is possible to change the capacitance of the variable capacitance diode 520 and switch the tuning frequency of the antenna 410 at the time of transmission and at the time of reception. Therefore, as shown in fig. 12, the tuning frequency of the antenna 410 is set to the transmission frequency (f)_rt1) Wherein the electromagnetic wave intensity of the upper sideband is high at the time of transmission and the tuning frequency of the antenna 410 can be set to the same receiving frequency as the carrier frequency at the time of reception. Further, as shown in fig. 13, by inverting the characteristics of the variable capacitance diode 520, the characteristics are reversedThe tuning frequency of the antenna 410 is set to the transmission frequency (f)_rt2) Wherein the electromagnetic wave intensity of the upper sideband is high, and the reception frequency can be set to the carrier frequency.

Therefore, with the second example of the reader/writer 400 according to the embodiment of the present invention, the number of configuration elements for switching the tuning frequency can be reduced as compared with the reader/writer 400 according to the first example, so that the size of the circuit can be suppressed.

With the reader/writer 400 according to the embodiment of the present invention, the capacitance of the tuning frequency adjustment circuit 500 can be changed, so that the tuning frequency of the antenna 410 can be switched to a reception frequency or a transmission frequency.

Therefore, according to the embodiments of the present invention, the tuning frequency of the antenna can be switched by changing the capacitance of the tuning frequency adjustment circuit when transmitting the electromagnetic wave from the tuning frequency control circuit and when receiving the electromagnetic wave from the tuning frequency control circuit. Therefore, high-speed communication between the noncontact IC card and the reader/writer can be realized.

Note that, with the embodiments of the present invention, description is given of examples of a noncontact IC card and a reader/writer, but the present invention is also applicable to a portable terminal and a noncontact IC card.

It is noted that the embodiments of the present invention have been described exemplarily to give a detailed description about the present invention while ensuring support of claims, but the present invention is not limited to the described embodiments accordingly, but various modifications can be made within the spirit and scope of the present invention.

Further, the processing order described according to the embodiment of the present invention may be provided as a method having the series of programs, and may also be provided as a program to execute the series of programs by a computer and a recording medium storing the program. As the recording medium, a recording medium such as a CD (compact disc), an MD (mini disc), a DVD (digital versatile disc), a memory card, a blu-ray disc (registered trademark), or the like can be used.

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and improvements may be made in accordance with design requirements and other factors, and are intended to be included within the scope of the claims or equivalents of the present invention.

Claims (18)

1. A transponder, comprising:

an antenna circuit that performs communication with an interrogator that is a communication target via an electromagnetic wave,

wherein the antenna circuit is composed of a coil and a variable capacitance circuit which are connected in parallel with each other,

wherein, in case of receiving a data signal by the antenna circuit, the tuning frequency thereof is a first frequency; and

and a tuning frequency control circuit that switches a tuning frequency of the coil and the variable capacitance circuit connected in parallel to each other to a second frequency when a data signal is transmitted through the antenna circuit.

2. The transponder of claim 1 wherein the tuned frequency control circuit switches the tuned frequency to the second frequency prior to transmission of the data signal through the antenna circuit when data processing of data received from the interrogator is complete.

3. The transponder of claim 2 wherein the tuned frequency control circuit switches the tuned frequency to the first frequency after transmitting the results of the data processing to the interrogator via the antenna circuit.

4. The transponder of claim 2, wherein the tuning frequency control circuit switches the tuning frequency to the first frequency if a power supply voltage generated by an alternating voltage induced in the antenna circuit via electromagnetic waves from the interrogator is lower than a predetermined voltage.

5. The transponder of claim 1, wherein the first frequency is a frequency higher than a peak of a sideband with a high frequency of sidebands transmitted from the interrogator.

6. The transponder of claim 1, wherein the first frequency is a frequency lower than a peak of one of sidebands transmitted from the interrogator that has a low frequency.

7. The transponder of claim 1 wherein the tuned frequency control circuit switches the tuned frequency to the second frequency by controlling the variable capacitance circuit.

8. The transponder of claim 1,

the variable capacitance circuit includes:

a first fixed capacitive element and a switch connected directly, an

A second fixed capacitive element connected in parallel to the directly connected first fixed capacitive element and the switch,

wherein the tuning frequency control circuit changes the capacitance of the variable capacitance circuit by controlling the switch and switches the tuning frequency to the second frequency.

9. The transponder of claim 1,

the variable capacitance circuit comprises a variable capacitance diode; and is

Wherein the tuning frequency control circuit switches the tuning frequency to the second frequency by controlling a capacitance of the variable capacitance diode.

10. An interrogator, comprising:

an antenna circuit configured by a coil and a variable capacitance circuit connected in parallel to each other to perform communication with a transponder as a communication object via electromagnetic waves; and

the frequency control circuit is tuned in such a way that,

switching the tuning frequency of the antenna circuit to a first frequency in case of transmitting a data signal from the antenna circuit,

switching the tuning frequency of the antenna circuit to a second frequency in case of receiving a data signal transmitted with the transponder.

11. The interrogator of claim 10, wherein the tuned frequency control circuit switches the tuned frequency of the antenna circuit to the second frequency after transmitting data to be transmitted to the transponder via the antenna circuit.

12. The interrogator of claim 11, wherein the tuning frequency control circuit switches the tuning frequency of the antenna circuit to the first frequency prior to transmission of a data signal from the antenna circuit when response data processing with respect to the data from the transponder is finished.

13. The interrogator of claim 10, wherein the first frequency is a frequency higher than a peak of a sideband with a high frequency of sidebands transmitted from the antenna circuit.

14. The interrogator of claim 10, wherein the first frequency is a frequency lower than a peak of a sideband with a low frequency of sidebands transmitted from the antenna circuit.

15. The interrogator of claim 10, wherein the tuned frequency control circuit switches the tuned frequency of the antenna circuit to the first frequency or the second frequency by controlling the variable capacitance circuit.

16. The interrogator of claim 10, wherein,

the variable capacitance circuit includes:

a first fixed capacitive element and a switch connected directly, an

A second fixed capacitive element connected in parallel to the directly connected first fixed capacitive element and the switch,

wherein the tuning frequency control circuit changes a capacitance of the variable capacitance circuit by controlling the switch, and switches the tuning frequency of the antenna circuit to the first frequency or the second frequency.

17. The interrogator of claim 10, wherein,

the variable capacitance circuit comprises a variable capacitance diode;

wherein the tuning frequency control circuit switches the tuning frequency of the antenna circuit to the first frequency or the second frequency by controlling a capacitance of the variable capacitance diode.

18. A communication device, comprising:

an antenna circuit configured by a coil and a variable capacitance circuit connected in parallel to each other to perform communication with another communication apparatus as a communication object via electromagnetic waves; and

the frequency control circuit is tuned in such a way that,

in the case of receiving a data signal from the other communication device, switching the tuning frequency of the antenna circuit to a first frequency, an

Switching the tuning frequency of the antenna circuit to a second frequency in case of transmitting a data signal transmitted with the antenna circuit.