JPH1145319A - Data carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the rise of a voltage more than needed when the distance between a base unit and a hand set is comparatively shortened. SOLUTION: Signals from the base unit are received by a tuner circuit composed of an antenna coil 1 and tuning capacitors 2 and 3. While parallelly connecting the tuning capacitor 3 and a variable capacity diode 5, further, the tuning capacitor 2 is serially connected. In order to obtain power to be used in a data carrier, a voltage is rectified by a diode 4. The rectified voltage is detected by a resistor 6 and applied to the variable capacity diode 5. When the distance between the data carrier and the base unit changes and the rectified voltage rises, the capacity of the variable capacity diode 5 changes, the tuning frequency of the tuner circuit is gradually deviated from the frequency of signals from the base unit, and an induced voltage is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data carrier and, more particularly, to a non-contact type IC card type data carrier for exchanging signals between a master unit and a slave unit (data carrier).

[0002]

2. Description of the Related Art A non-contact type IC card system for transmitting and receiving signals between a parent device and a card of a child device by an electromagnetic coupling method or an electromagnetic induction method is widely known. In particular, batteryless non-contact IC card type data carriers that rectify a carrier wave on the slave device side and use it as power for the slave device have been widely used as ID cards, tags for recognizing goods, and the like. Have been.

In such an electromagnetic coupling type non-contact type IC card system, a base unit modulates a carrier generated by an OSC (oscillator) according to transmission data, and amplifies the modulated wave by a driver circuit. Then, the antenna coil is driven and transmitted to the slave unit. When the slave unit receives a signal from the master unit with the antenna coil, the rectifier circuit rectifies the carrier wave to obtain power for internal use, and the demodulation circuit demodulates the received signal and sends it to the data processing circuit to perform data processing. Data processing is performed by the circuit.

[0004] By the way, the power used in the slave unit is generated by rectifying a signal received from the master unit by a rectifier circuit. In order to enhance the selectivity of a signal from the master unit, the slave unit is provided with an antenna coil. In many cases, a tuning resonance circuit is formed by connecting capacitors in parallel. Tuning frequency f of this resonant circuit
0 is determined by the inductance L of the antenna coil and the capacitance C of the capacitor. Tuning frequency f0
Is adjusted to the frequency of the carrier wave, the coupling between the master unit and the slave unit is strengthened, and sufficient power can be obtained even if the distance between the master unit and the slave unit is large.

[0005]

However, in the conventional data carrier system, in order to ensure a sufficient distance between the master unit and the slave unit, sufficient power can be obtained even at a preset maximum communication distance. , The parameters of the rectifier circuit are set. Then, when the distance between the master unit and the slave unit becomes short, a large voltage is generated in the tuning circuit, and each component of the rectifier circuit must have a withstand voltage enough to withstand this high voltage. This has led to an increase in parts cost and size. This problem becomes a serious problem when the circuit is formed into an IC. Furthermore, the rectified output is regulated in order to keep the operating voltage of the internal circuit within a certain range, but there has been a problem that heat generation in the regulated circuit increases.

An object of the present invention is to solve the above-mentioned problems of the prior art. When the distance between the master unit and the slave unit becomes relatively short, data which can suppress an unnecessary rise in voltage can be suppressed. The purpose is to provide a career.

[0007]

To achieve the above object, a data carrier according to the present invention comprises a receiving coil, a resonant capacitor connected in parallel with the receiving coil to form a tuning circuit, and a signal received by the receiving coil. Demodulation means for demodulating the signal, signal processing means for performing various signal processing based on the signal demodulated by the demodulation means, and power supply means for rectifying the signal received by the receiving coil to generate power to the signal processing means. Is provided with a variable capacitance diode connected to the resonance capacitor, and the capacitance of the variable capacitance diode is changed in proportion to the output voltage of the power supply means.

When the distance between the master unit and the slave unit is short and the output voltage of the power supply means rises, the capacity of the variable capacitance diode is changed to deliberately shift the tuning frequency of the tuning circuit from the frequency of the received signal. As a result, the induction voltage of the coil of the slave unit decreases. Therefore, an increase in the voltage obtained from the rectifier circuit can be suppressed. Further, in order to achieve the above object, the data carrier of the present invention includes a receiving coil, a resonance capacitor connected in parallel with the receiving coil to form a tuning circuit, and a demodulating means for demodulating a signal received by the receiving coil. A data carrier comprising signal processing means for performing various signal processing based on the signal demodulated by the demodulation means, and power supply means for rectifying the signal received by the receiving coil to generate power for the signal processing means. The tuning circuit changes the tuning frequency according to the output voltage of the power supply means. As a result, the fluctuation range of the output voltage of the power supply means can be reduced, and the withstand voltage of components constituting the data carrier, particularly components used in the rectifier circuit, can be reduced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a non-contact type IC card type data carrier will be described below with reference to the drawings. FIG. 1 shows a block diagram of a data carrier according to an embodiment of the present invention. The data carrier of the embodiment of the present invention shown in FIG. 1 includes an antenna coil 1, tuning capacitors 2, 3, a rectifier diode 4, a resistor 6, a variable capacitance diode 5, a smoothing capacitor 8, a signal processing circuit 9, and a demodulation circuit 10. Having. There is also a data carrier configured to transmit data from the data carrier by adding a modulation circuit (not shown), but this is not shown because it does not directly relate to the description of the present invention.

The antenna coil 1 receives an electromagnetic wave from a transmission coil of a master unit (not shown) and electromagnetically couples. The induced voltage generated by the electromagnetic coupling at this time is the highest when the tuning frequency of the tuning circuit composed of the antenna coil 1 and the tuning capacitors 2 and 3 is the same as the transmission frequency, and can rapidly decrease as the frequency shifts. Are known. Also, the induced voltage decreases as the distance between the master unit and the slave unit increases. It is desirable to always obtain a constant voltage as the power supply used in the data carrier of the slave unit. However, when it is used as an ID card, a tag for recognition of a conveyed object, etc., it is necessary to enter a certain detection area. Is often the only condition for detection.
It is not uncommon for the distance between the data carrier and the parent device to vary from tens of centimeters to several centimeters. In order to keep the output voltage of the power supply circuit constant as much as possible even if the distance between the data carrier and the base unit greatly changes in this way (especially so as not to exceed the maximum permissible voltage that causes destruction of components), It is connected in parallel with the tuning capacitor 3.
An output voltage V output to both ends of the smoothing capacitor 8 is applied between the anode and the cathode of the variable capacitance diode 5 via the resistor 6.

Tuning capacitor 3 and variable capacitance diode 5
Are connected in parallel, and a tuning capacitor 2 is further connected in series. Further, a large resistor 6 is connected to the tuning capacitor 2 in parallel. Tuning capacitor 2 and resistor 6
Is set to be 100 times or more the period of the signal frequency. The tuning capacitor 2 is a variable capacitance diode 5
In addition, there is an effect that the DC bias applied to the capacitor does not cause a short circuit in the antenna coil, the effect that the variable capacitance diode 5 itself rectifies and holds the charged electric charge, and an effect that the AC amplitude applied to the variable capacitance diode 5 is reduced.

Regarding the setting of the tuning capacitors 2 and 3 and the variable capacitance diode 5, under the condition that a DC bias is applied to the variable capacitance diode 5 when the lower limit induced voltage at which the slave unit can operate is generated in the tuning circuit, It is set so that a change in the tuning frequency of about 10% or more occurs at the maximum induced voltage that is tuned to the signal frequency from the input and is to be allowed.

A specific example will be described. When the signal frequency from the master unit is 125 KHz and the inductance of the antenna coil 1 is 1 mH, the tuning is accurately tuned when the tuning capacitance is 1621 pF as a whole, and the tuning capacitance is reduced by 10% to 1340 pF. It is time. The internal circuit of the contactless IC card, which is a data carrier, operates from an internal power supply of 2V, and the induced voltage to the tuning circuit at that time is 5V.
If it is assumed that a variable capacitance diode having a variation width of about 500 to 20 pF for an AM tuner is adopted, the target condition can be satisfied by the constants shown in FIG. That is, the capacity of the tuning capacitor 32 is 7100p
F, the capacitance of the tuning capacitor 33 is 1500 pF, and the resistance is 3
6 has a resistance of 100 KΩ.

By the way, in the example of FIG. 3, two variable capacitance diodes 34 and 35 are arranged in parallel, but a product in which two or more variable capacitance diodes are actually collected is generally easily available. It is confirmed from the example of FIG. 3 that when a DC bias of 2 V is applied to the variable capacitance diodes 34 and 35, each of the capacitances becomes 300 pF.
And the overall tuning capacitance is approximately 1621 pF. Furthermore, when the DC bias becomes 5.5 V, the capacitances of the variable capacitance diodes 34 and 35 become 65 pF, respectively, and reach 1326 pF as a whole, achieving the target. The induced voltage to the tuning circuit when a DC bias of 5.5 V is generated is 12 Vp-p.

FIG. 4 shows the effect of this embodiment. In this figure, in the conventional example (indicated by reference numeral A), when the coupling between the master unit and the antenna of the data carrier becomes strong, 30 Vp
−p or more, but in the present embodiment (indicated by the symbol B), it has increased only to 11 Vp-p. In this example, the voltage induced in the tuning circuit is 35 Vp-p and I
Although the breakdown voltage limit of C is reached, neither is a problem in this regard. On the other hand, the voltage induced in the tuning circuit reaches a limit due to heat generation due to continuous application at 26 Vpp, but this is a problem in the conventional example, and it is understood that it is necessary to reduce the signal of the master unit. Naturally, the limit distance of the operation is short. On the other hand, according to the present invention, the distance is extended by raising the signal level of the parent device if necessary, since the voltage is held down to 11 Vp-p. It should be noted that the data in FIG. 4 is created on the assumption that the diameter of the antenna coil 1 of the data carrier is sufficiently smaller than the diameter of the transmission coil of the master unit.

FIG. 2 is a circuit diagram showing a data carrier device according to a second embodiment of the present invention. In this embodiment, a full-wave rectifier circuit is used as a rectifier circuit. The data carrier according to the embodiment of the present invention shown in FIG. 2 includes an antenna coil 1, tuning capacitors 11, 12, 13, a rectifying diode bridge circuit 19, resistors 16, 17, 18, variable capacitance diodes 14, 15, and a smoothing capacitor 20. , A signal processing circuit 21, and a demodulation circuit 10. In this embodiment, the tuning capacitor 12 is used as the tuning capacitor of the tuning circuit, and the tuning frequency is substantially determined by the combined capacitance of the series circuit of the tuning capacitor 11 and the tuning capacitor 13. One output terminal A of the rectifier diode bridge circuit 19 is connected to the anode terminals of the variable capacitance diodes 14 and 15 via resistors 16 and 18, and the other output terminal B of the rectifier diode bridge circuit 19 is connected to the cathode terminal. A voltage obtained by dividing the output voltage supplied to both ends of the smoothing capacitor 10 by resistance is applied between the anode and the cathode of the variable capacitance diodes 14 and 15. Therefore, by changing the capacitance of the variable capacitance diodes 14 and 15 in accordance with the change in the output voltage of the power supply circuit and changing the tuning frequency, the power supply circuit can be used when the distance between the master unit and the slave unit is relatively short. Can be suppressed when the output voltage rises. By connecting the variable capacitance diodes in the reverse direction, there is an effect of suppressing distortion here and keeping Q high.

Of course, when the distance between the master unit and the slave unit is relatively short, in order to suppress an unnecessary rise in voltage,
There is also a method of limiting the voltage using a Zener diode or the like, but in this case, energy corresponding to the voltage higher than the Zener voltage is consumed as heat, and the temperature of the data carrier increases, which is not preferable. . On the contrary,
In the present invention, since the strength of electromagnetic coupling is only weakened, problems such as heat generation do not occur.

[0018]

According to the present invention, an unnecessary rise in voltage can be suppressed when the distance between the master unit and the slave unit is relatively short. Further, the withstand voltage of the components constituting the data carrier, particularly the components used for the rectifier circuit, can be kept low.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a data carrier according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a data carrier according to another embodiment of the present invention.

FIG. 3 is a circuit diagram of a data carrier describing specific constants according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a change in induced voltage when the capacitances of variable capacitance diodes 33 and 34 are changed in the circuit of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna coil 2, 3 Tuning capacitor 4 Rectifier diode 5 Variable capacitance diode 6 Resistance 8 Smoothing capacitor 9 Signal processing circuit 10 Demodulation circuit

Claims (6)

[Claims] 1. A receiving coil, a resonance capacitor connected in parallel with the receiving coil to form a tuning circuit, a demodulating means for demodulating a signal received by the receiving coil, and a signal demodulated by the demodulating means. A data carrier comprising signal processing means for performing various signal processing based on the signal, and power supply means for generating power to the signal processing means by rectifying a signal received by the receiving coil, the power supply means, A data carrier comprising a variable capacitance diode connected to a resonance capacitor, wherein a capacitance of the variable capacitance diode changes according to an output voltage of the power supply means. 2. The variable capacitance diode according to claim 1, wherein the capacitance of said variable capacitance diode changes so as to shift the tuning frequency of said tuning circuit from the frequency of a received signal when the output voltage of said power supply means rises. Data carrier to do. 3. The device according to claim 1, wherein the resonance capacitor has at least two or more capacitors connected in series, and the variable capacitance diode is connected in parallel to one of the capacitors connected in series. A data carrier characterized by the following. 4. A receiving coil, a resonance capacitor connected in parallel with the receiving coil to form a tuning circuit, demodulating means for demodulating a signal received by the receiving coil, and a demodulating means for demodulating the signal received by the demodulating means. In a data carrier comprising signal processing means for performing various signal processing in the original, and power supply means for rectifying a signal received by the receiving coil to generate power to the signal processing means, wherein the tuning circuit comprises: A data carrier characterized by changing a tuning frequency according to an output voltage of a power supply means. 5. The data carrier according to claim 4, wherein the tuning circuit changes a tuning frequency so that an output voltage of the power supply does not exceed a predetermined voltage. 6. The tuning circuit according to claim 4, wherein the tuning circuit changes the tuning frequency in a direction shifted from the frequency of the received signal when the output voltage of the power supply means rises at least beyond a predetermined voltage. Data carrier.