JP2001005938A - Non-contact ic card - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the communication distance from being reduced and a failure in data reading from occurring without increasing the consumption current of a reader/writer even when the resonance frequency of an IC card deviates. SOLUTION: The resonance circuit 11 of an IC card 3 consists of an antenna coil 14 and a resonance circuit controlling part 5. The circuit 11 outputs a direct current voltage from a rectifying part 6 by receiving an electromagnetic signal for power from a reader/writer. Here, the part 5 is made to control the resonance frequency of the circuit 11 so that the direct current voltage from the part 6 can be maximum. Accordingly, the card 3 can perform communications in a resonance state with the reader/writer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-contact type IC card for exchanging data with a reader / writer.

2. Description of the Related Art In recent years, attempts have been made to replace employee cards, commuter passes, telephone cards, and the like from magnetic cards to non-contact IC cards. Since this type of IC card does not have a built-in power supply, power is supplied by transmitting a power electromagnetic wave signal from the reader / writer to the IC card, and the reader / writer exchanges data with the IC card in the power supply state. Generally, the resonance frequency of the resonance circuit of the IC card matches the frequency of the power signal. Specifically, the values of the antenna coil and the capacitor are selected so as to resonate at a predetermined frequency, and the resonance frequency of the resonance circuit is fixedly set in the IC card.

[0002]

However, the above configuration has the following problems. (1) The resonance frequency of the IC card shifts due to variations in the capacitance of the antenna coil and the capacitor. (2) When the resonance frequency is adjusted by an IC card alone, or when a plurality of IC cards are overlapped, the resonance frequency of the IC card is shifted due to mutual coupling between the IC cards. (3) If the IC card gets wet with water, the resonance frequency of the IC card shifts.

[0003] When the resonance frequency of the IC card is shifted as described above, the communication distance between the reader / writer and the IC card is shortened, or the reader / writer cannot reliably read data from the IC card. is there.

In this case, in order to solve the above problem, it is conceivable to increase the output on the reader / writer side.
There are the following restrictions, which cannot be completely solved.

(1) The upper limit of the output of a reader / writer is determined by regulations such as the electromagnetic wave law. (2) In recent years, there is a high demand for power saving, and current consumption must be suppressed. The present invention has been made in view of the above circumstances, and its purpose is to reduce the communication distance with the reader / writer without increasing current consumption and to reduce data transfer by the reader / writer even when the resonance frequency is shifted. Non-contact type I that can prevent inconvenience in reading
To provide a C card.

[0006]

According to the first aspect of the present invention, when the resonance frequency of the resonance circuit deviates from the frequency of the electromagnetic wave signal from the reader / writer, the DC voltage from the rectification unit decreases. However, since the resonance frequency control unit controls the resonance frequency of the resonance circuit so that the DC voltage from the rectification unit is maximized, the resonance frequency of the resonance circuit is controlled to the frequency that resonates with the reader / writer, and the reader / writer and the IC The communication distance with the card can be prevented from being shortened.

According to the second aspect of the present invention, when the DC voltage output from the rectifier is low, there is a possibility that the deviation of the resonance frequency of the resonance circuit is large and the communication by the control circuit may be defective. Since the operation of the control circuit is stopped until the DC voltage detected by the detection unit reaches the predetermined voltage, the control circuit operates with the resonance circuit adjusted to an appropriate resonance frequency.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The outline of the present invention will be described below with reference to FIGS. FIG. 2 schematically shows the entire configuration of the present invention. In FIG. 2, the reader / writer 1 has an antenna coil 2 and the IC card 3 has an antenna coil 4. An electromagnetic wave signal for power is transmitted from the antenna coil 2 of the reader / writer 1 to the antenna coil 4 of the IC card 3. The reader / writer 1 sends an IC
Data can be exchanged with the card 3. Incidentally, the antenna coil 4 is generally built in the IC card 3.

FIG. 1 schematically shows the configuration of the IC card 3. In FIG. 1, an IC card 3 includes an antenna coil 4 and a capacitor 4 for transmitting and receiving an electromagnetic wave signal.
a, a resonance frequency control unit 5 for controlling the resonance frequency,
It comprises a rectifier 6, a smoothing capacitor 7, a control / arithmetic unit 8, a clock generator 9, a memory 10, and the like.

The antenna coil 4, the capacitor 4a, and the resonance frequency control unit 5 are connected in parallel to form a resonance circuit 11.
The resonance circuit 11 receives a power electromagnetic wave signal of a predetermined frequency from the reader / writer 1 and converts it into a power signal. The rectifier 6 rectifies the power signal output from the resonance circuit 11, smoothes the signal to a constant DC voltage (operating voltage) by the smoothing capacitor 7, and outputs the DC voltage to each circuit.

A signal such as data transmitted from the reader / writer 1 is transmitted by being superimposed on a power electromagnetic wave signal, and the signal is demodulated by the receiving unit 12 and is transmitted to the control / arithmetic unit 8. Given to. The control / calculation unit 8
Performs processing according to the signal input from the receiving unit 12,
The data stored in the memory 10 is modulated by the modulation unit 13 and transmitted from the antenna coil 4 while being superimposed on the power electromagnetic wave signal.

Here, if the resonance frequency of the resonance circuit 11 deviates from the electromagnetic wave frequency f0 of the reader / writer 1 due to various factors, the communication distance between the reader / writer 1 and the IC card 3 decreases, or the reader / writer 1 The reading of data from the IC card 3 by the data may be uncertain.

Therefore, in the present invention, the deviation of the resonance frequency is prevented by controlling the resonance frequency by the resonance frequency control unit 5 as follows. That is, as shown in FIG. 3, the DC voltage from the rectifying unit 6 drops from the original voltage V2 to V1 or V3, so that the resonance frequency control unit 5 determines the resonance frequency of the resonance circuit 11 based on the DC voltage. Was controlled. That is, when the resonance frequency f of the resonance circuit 11 is f> f0 and f <f0 with respect to the electromagnetic wave frequency f0 of the reader / writer 1, the DC voltage from the rectifying unit 6 decreases from the maximum voltage V2 and f = f0. Since the DC voltage from the rectifier 6 becomes the maximum voltage V2, it is possible to determine whether the resonance circuit 11 has resonated with the reader / writer 1 based on the DC voltage from the rectifier 6.

Therefore, by controlling the resonance frequency of the resonance circuit 11 so that the DC voltage from the rectification unit 6 is maximized, the resonance circuit 11 can be controlled so as to be in resonance with the reader / writer 1. Thereafter, the reader / writer 1 and the IC card 3 resonate, and the reader / writer 1 can reliably communicate with the IC card 3.

Here, the resonance frequency control unit 5 includes a capacitor capacitance control method as shown in FIG. 4 and a resonance circuit resistance control method to control the impedance of the capacitor 14 as shown in FIG. The resonance frequency in the control method is f0 = 1 / (2.pi. (LC)
^1/2 ), and the resonance frequency in the resonance circuit resistance control method is f0 = 1 / (2 ・ π ・ (LC-C
Can be represented by ² R ^{2) 1/2).}

FIG. 6 shows a capacitor capacity method.
As shown in FIG. 7, there are a switch switching system using a plurality of switches 15 for selecting the capacitor 14 and a variable capacitor system using a variable capacitor 16 as shown in FIG. There is a transistor control method using a transistor 17 as shown in FIG.

(First Embodiment) Next, a first embodiment of the present invention will be described with reference to FIGS. In the first embodiment, a variable capacitor method in a capacitor capacity control method is employed as a resonance frequency control unit.

FIG. 9 shows the configuration of the resonance frequency control unit 5. In FIG. 9, the resonance frequency control unit 5 includes an IC
The capacitor 14 is connected to the gate of the FET 18 and the DC voltage from the rectifier 6 is connected to the gate of the FET 18.
1 and are connected so as to be applied.

Here, the junction capacitance Cgs between the gate and the source of the FET 18 (see FIG. 10) has a characteristic that the capacitance decreases as the voltage Vg between the gate and the source increases as shown in FIG. Accordingly, as shown in FIG. 12, the resonance frequency of the resonance circuit 11 has such a characteristic that it increases as the DC voltage increases. In this case, the resonance frequency control unit 5 sets the initial resonance frequency of the resonance circuit 11 to the reader / writer 1.
Is set lower than the electromagnetic wave frequency f0.

Next, the operation of the above configuration will be described. The reader / writer 1 transmits a power electromagnetic wave signal having a reference frequency from the antenna coil 2.

In the IC card 3, a power electromagnetic wave signal from the reader / writer 1 is received by the antenna coil 4,
A power signal is output from the resonance circuit 11. This power signal is generated as a DC voltage by the rectifier 6 and output to each circuit as an operating voltage.

Now, as the IC card 3 approaches the reader / writer 1, the DC voltage from the rectifier 6 rises. At this time, as shown in FIG. 12, the resonance frequency of the resonance circuit 11 rises as the DC voltage rises, while as shown in FIG. 3, the DC voltage rises as the resonance frequency approaches the electromagnetic wave frequency f0. As it rises, the capacity C
When gs decreases and the resonance frequency rises, the DC voltage further rises, so that a positive feedback is performed, and the DC voltage rises at once. Then, when the resonance frequency becomes the electromagnetic wave frequency f0, the DC voltage becomes maximum, and when the resonance frequency exceeds the electromagnetic wave frequency f0, the DC voltage starts to decrease.
Will be adjusted automatically. Therefore, hereinafter, communication with the reader / writer 1 is performed in a state where the resonance frequency of the resonance circuit 11 is adjusted to the electromagnetic wave frequency f0.

According to such an embodiment, the FET 1
8, the resonance frequency of the resonance circuit 11 of the IC card 3 is automatically adjusted to be the electromagnetic wave frequency f0 from the reader / writer 1, so that the resonance frequency of the resonance circuit 11 is fixed. Unlike the one described above, the communication distance between the reader / writer 1 and the IC card 3 is prevented from being reduced, and there is no problem in reading data from the IC card 3 by the reader / writer 1.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
The embodiment will be described with reference to FIGS.
In the second embodiment, the resonance frequency control unit 5
This adopts a switch switching method in the capacitor capacity control method.

FIG. 13 shows the configuration of the resonance frequency control unit 5. In FIG. 13, a capacitor 14 is an FET
19, and a capacitor switching unit 20 is connected to the gate of the FET 19, and when the selected FET 19 is turned on, the resonance circuit 11 is turned on.
And the resonance frequency of the resonance circuit 11 is controlled. This capacitor switching unit 20
As shown in FIG. 14, a plurality of voltage comparison circuits 21 are provided, and the voltage comparison circuit 21 controls the resonance frequency by turning on the connected FET 19 when the DC voltage exceeds a predetermined switching set voltage. It is supposed to. In this case, the resonance circuit 11 has such a characteristic that the resonance frequency decreases stepwise as the DC voltage increases, as shown in FIG. Further, the capacitor switching unit 20 sets the initial resonance frequency of the resonance circuit 11 higher than the electromagnetic wave frequency f0 of the reader / writer 1.

When the DC voltage from the rectifier 6 rises as the IC card 3 approaches the reader / writer 1,
As shown in FIG. 15, the resonance frequency of the resonance circuit 11 decreases stepwise as the DC voltage rises, while the DC voltage rises as the resonance frequency approaches the electromagnetic wave frequency f0 as shown in FIG. Since the DC voltage rises, a positive feedback that the DC voltage further rises when the resonance frequency lowers is performed, and the DC voltage rises at a stretch. When the resonance frequency becomes the electromagnetic wave frequency f0, the DC voltage becomes maximum, and when the resonance frequency becomes lower than the electromagnetic wave frequency f0, the DC voltage starts to decrease. Will be automatically adjusted. Therefore, hereinafter, communication with the reader / writer 1 is performed in a state where the resonance frequency of the resonance circuit 11 is adjusted to the electromagnetic wave frequency f0.

According to the second embodiment, when the predetermined FET 19 is turned on by the capacitor switching unit 20, the switching is performed so that the resonance frequency of the resonance circuit 11 decreases as the DC voltage increases. So the first
As in the first embodiment, the resonance frequency of the resonance circuit 11 can be automatically adjusted to the electromagnetic wave frequency f0 of the reader / writer 1 to prevent the communication distance between the reader / writer 1 and the IC card 3 from being reduced, and to reduce There is no problem in reading the data of the IC card 3 by the writer 1.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIGS. In the third embodiment, the resonance frequency control section 5 employs a transistor control method in a resonance circuit resistance control method.

That is, in FIG. 16 showing the resonance frequency control unit 5, a transistor 22 is connected in series to a capacitor 14, and a DC voltage divided by resistors 23 and 24 is applied to the base of the transistor 22. And the resonance circuit 1 according to the transistor 22 to be turned on.
1 is controlled. In this case, since the resistance between the collector and the emitter of the transistor 22 increases as the base voltage of the transistor 22 increases, the resonance frequency of the resonance circuit 11 decreases as the DC voltage increases, as shown in FIG. It shows characteristics. The initial resonance frequency of the resonance circuit 11 is set higher than the electromagnetic wave frequency f0 of the reader / writer 1.

When the DC voltage from the rectifier 6 rises as the IC card 3 approaches the reader / writer 1,
As shown in FIG. 17, the resonance frequency of the resonance circuit 11 decreases as the DC voltage increases, while the DC voltage increases as the resonance frequency decreases so as to approach the electromagnetic wave frequency f0 as shown in FIG. When the resonance frequency decreases, the DC voltage further rises, so that a positive feedback is performed, and the DC voltage rises at a stretch. When the resonance frequency becomes the electromagnetic wave frequency f0, the DC voltage becomes maximum, and when the resonance frequency becomes lower than the electromagnetic wave frequency f0, the DC voltage starts to decrease. Will be automatically adjusted. Therefore, hereinafter, communication with the reader / writer 1 is performed in a state where the resonance frequency of the resonance circuit 11 is adjusted to the electromagnetic wave frequency f0.

According to the third embodiment, the resonance frequency of the resonance circuit 11 is controlled by adjusting the resistance between the collector and the emitter of the transistor 22 according to the DC voltage. Therefore, similarly to the first embodiment, the resonance frequency of the resonance circuit 11 is
The electromagnetic wave frequency f0 can be automatically adjusted to prevent the communication distance between the reader / writer 1 and the IC card 3 from being reduced, and there is no problem in reading data from the IC card 3 by the reader / writer 1.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIG. The feature of the fourth embodiment is that the control circuit is operated in accordance with the DC voltage.

That is, the IC card 3 is provided with a voltage detecting section 25. When the detected DC voltage is lower than the specified voltage, the voltage detecting section 25 controls / calculates (corresponds to a control circuit). 8 and clock generator (corresponding to control circuit)
9 is stopped.

Therefore, when the DC voltage is low and the resonance frequency deviates from the electromagnetic wave frequency f0 of the reader / writer 1, the control / calculation unit 8 and the clock generation unit 9 do not operate, and the DC voltage becomes sufficiently high. When the resonance frequency becomes the electromagnetic wave frequency f0 of the reader / writer 1, the arithmetic / control unit 8 and the clock generation unit 9 operate.

According to the fourth embodiment, the communication with the reader / writer 1 is performed while the resonance frequency of the resonance circuit 11 of the IC card 3 is controlled to the electromagnetic wave frequency f0 of the reader / writer 1. Communication with the reader / writer is not performed while the voltage is low, and there is no problem in reading data from the IC card 3 by the reader / writer 1.

The present invention is not limited to the above embodiments, but can be modified or expanded as follows.
In the first embodiment, a varicap diode may be connected instead of the FET, and the resonance frequency of the resonance circuit 11 may be controlled by adjusting the control voltage of the varicap diode.

In the fourth embodiment, the voltage detector 2
5, the power supply path to the control / calculation unit 8 and the clock generation unit 9 may be cut off.

The resonance frequency of the resonance circuit 11 may be continuously changed to control the resonance frequency at which the DC voltage from the rectification unit 6 becomes maximum.

[Brief description of the drawings]

FIG. 1 is a block diagram of an IC card for explaining an outline of the present invention.

FIG. 2 is a schematic diagram showing the overall configuration.

FIG. 3 is a diagram showing a relationship between a frequency and a DC voltage.

FIG. 4 is an electric circuit diagram showing a resonance frequency control unit of a capacitor capacity control method.

FIG. 5 is an electric circuit diagram showing a resonance frequency control unit of a resonance circuit resistance control method.

FIG. 6 is an electric circuit diagram showing a switch switching method in a capacitor capacity method.

FIG. 7 is an electric circuit diagram showing a variable capacitor system in the capacitor system.

FIG. 8 is an electric circuit diagram showing a transistor control method in a resonance circuit resistance control method.

FIG. 9 is an electric circuit diagram showing a resonance frequency control unit according to the first embodiment of the present invention.

FIG. 10 is a diagram showing a junction capacitance of an FET.

FIG. 11 is a diagram showing a relationship between a gate voltage and a junction capacitance of an FET.

FIG. 12 is a diagram showing a relationship between a DC voltage and a resonance frequency of an IC card.

FIG. 13 is a view corresponding to FIG. 9, showing a second embodiment of the present invention;

FIG. 14 is a schematic diagram showing a capacitor switching unit.

FIG. 15 is a diagram corresponding to FIG. 12;

FIG. 16 is a view corresponding to FIG. 9, showing a third embodiment of the present invention;

FIG. 17 is a diagram corresponding to FIG. 12;

FIG. 18 is a view corresponding to FIG. 9, showing a fourth embodiment of the present invention;

[Explanation of symbols]

1 is a reader / writer, 3 is an IC card, 5 is a resonance frequency control unit, 6 is a rectification unit, 8 is a control circuit, 9 is a clock generation unit (control circuit), 11 is a resonance circuit, and 25 is a voltage detection unit. is there.

Claims (4)

[Claims] 1. A non-contact IC card comprising: a resonance circuit that receives an electromagnetic wave signal from a reader / writer; and a rectifier that outputs a DC voltage in a state where the resonance circuit receives the electromagnetic wave signal from the reader / writer. A non-contact type IC card, comprising: a resonance frequency control unit that controls a resonance frequency of the resonance circuit so that a DC voltage from the rectification unit is maximized. 2. A voltage detection unit for detecting a DC voltage output from the rectification unit, wherein the operation of the control circuit is stopped until the voltage detected by the voltage detection unit reaches a predetermined voltage. The non-contact type IC card according to claim 1, wherein: 3. The non-contact IC card according to claim 1, wherein the resonance frequency control unit controls a resonance frequency of the resonance circuit by controlling a capacitance of the resonance circuit. 4. The non-contact IC card according to claim 1, wherein the resonance frequency control section controls a resonance frequency of the resonance circuit by controlling an impedance of the resonance circuit.