JP3884565B2 - Non-contact IC card reader / writer device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reader / writer device for a non-contact IC card.
[0002]
[Prior art]
The non-contact IC card does not have a power source in the IC card, and is supplied with electric power from a reader / writer device by electromagnetic coupling, and operates with the electric power. Data communication is also performed in a non-contact manner by the same electromagnetic coupling. FIG. 8 shows the power supply unit on the reader / writer device side and the power receiving system on the non-contact IC card side. The high frequency of the frequency fc output from the oscillator 1 is amplified by the amplifier 2, and the matching circuit 3 is To the antenna coil having the self-inductance L1. The antenna coil is directly connected to a tuning capacitor having a capacitance C1 in order to increase transmission efficiency. In the figure, R1 represents the loss resistance of this antenna coil.
[0003]
A tuning capacitor C2 is also connected in parallel to the antenna coil on the non-contact IC card side so as to resonate with the self-inductance L2 and increase the transmission efficiency. When the antenna coil on the non-contact IC card side is electromagnetically coupled with the antenna coil on the reader / writer device side, an induced voltage is generated, which is rectified by the diode circuit 4, adjusted to a predetermined voltage by the regulator 5, and sent to the IC circuit 6. Supplied.
[0004]
[Problems to be solved by the invention]
In the non-contact IC card, the range of the distance that the IC card can operate from the antenna coil of the reader / writer device is determined, and the position that receives the most power and the position that receives the least power in the operation range. There is a difference in the power received within this operating range. In order for the non-contact IC card to be stabilized within the operating range, the output of the reader / writer device is set so that the power necessary for the non-contact IC card to operate can be received at the position where the least power is received. Has been. Accordingly, energy other than the power required by the IC circuit in the non-contact IC card is extra at positions other than the position where the minimum power is received, and the regulator dissipates this extra power to obtain a predetermined output voltage. I have to. For this reason, even within the operation range of the non-contact IC card, the amount of heat generated from the regulator increases depending on the position, and becomes the maximum at the position where the most power is received. At this time, the IC may be directly damaged by the heat generated by the regulator, or the IC may be damaged by the deformation of the synthetic resin or the like that forms the IC card, and the input voltage allowed by the regulator If a larger voltage is applied, the regulator may be damaged. Such a problem is likely to occur particularly when the non-contact IC card is left in the operating range of the reader / writer device for a long time.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a reader / writer device for a non-contact IC card in which the IC is not damaged by heat generated by the overpower transmission to the non-contact IC card or the regulator is not damaged by the overvoltage. is there.
[0006]
[Means for Solving the Problems]
The present invention is a reader / writer device having a function of supplying power to a non-contact IC card by electromagnetic coupling of the antenna of the non-contact IC card and the antenna of the own device,
Power control means for controlling the high-frequency power supplied to the antenna of the device itself;
Detection means for detecting an input high-frequency voltage or current to the antenna of the device;
A coupling coefficient calculation means for obtaining a coupling coefficient between the antenna of the non-contact IC card and the antenna of its own device from the input high-frequency voltage or current detected by the means and the output voltage of the power control means;
Control means for controlling the output voltage of the power control means so that the received power of the non-contact IC card becomes a predetermined value from the coupling coefficient obtained by the means;
With
A non-contact IC comprising a second control means for reducing the output voltage of the power control means on condition that the high frequency voltage or current detected by the detection means does not change for a predetermined time or more. A card reader / writer device is disclosed.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing a configuration example of a reader / writer device according to the present invention, and shows only a portion related to power transmission. The same circuit as that of the conventional FIG. 8 is indicated by the same reference numeral, and in addition to the circuit indicated by the same reference numeral, a voltage detection circuit 11 for detecting the output high frequency voltage V (effective value) of the amplifier 2; A power control circuit 13 for variably controlling the output power is added. The reader / writer device IC 12 is conventionally provided for controlling the operation of the reader / writer device. The output signal of the voltage detection circuit 11 is also input to the IC 12.
[0010]
FIG. 2 is an equivalent circuit of the power transmission system of FIG. In this equivalent circuit, the power source 20 is a circuit composed of the oscillator 1 and the power control circuit 13 of FIG. 2, and its output voltage is Vs. Frequency fc = 13.56 MHz, amplifier 2 output impedance RS = 50Ω, reader / writer device antenna self-inductance L1 = 6.8 μH, card antenna self-inductance L2 = 1.5 μH, reader / writer device antenna loss R1 = 12.5Ω, C1 is resonated with L1 and C2 is resonated with frequency fc, respectively, and the matching circuit 3 matches the reader / writer device antenna and the output impedance Rs of the transmitter. Further, it is assumed that RL = 2.56 kΩ, which is a pseudo load of the card IC. If the mutual inductance of both antennas is M, the coupling coefficient k of both antennas is
k = M / (L1 / L2) ^1/2
Therefore, if this coupling coefficient k is given, M is determined. Therefore, when the output voltage Vs of the power source 20 is used as a parameter, and the output voltage V is changed using the equivalent circuit of FIG. The following results are obtained. That is, the output voltage V of the amplifier 2 increases as the coupling coefficient k increases. However, such a voltage V hardly changes when the output impedance Rs of the amplifier 2 is too small, but normally, a voltage with Rs = 50Ω or 75Ω is used, so that the voltage V varies with the change of the coupling coefficient k. Change.
[0011]
From the result of FIG. 3, it is understood that when the output voltage of the power source 20, that is, the output voltage Vs of the power control circuit 13 and the output V of the amplifier 2 are given, the value of the coupling coefficient k at that time is uniquely determined. Since the output voltage Vs of the power control circuit 13 is controlled by the IC 12, the value of Vs is known to the IC 12, and the output voltage V of the amplifier 2 is also known to the IC 12 from the output signal of the voltage detection circuit 11. Therefore, if the circuit characteristics as shown in FIG. 3 are given, the IC 12 can know the value of the coupling coefficient k at each time point.
[0012]
Specific examples of the method include the following. As can be easily seen from FIG. 3, the voltage V, which is a function of Vs and k, is proportional to the value of Vs. Therefore, [Equation 2]
V = Vs · f (k)
Call it. Therefore, for example, if f (k) for each value of k is obtained from V / Vs for an arbitrary Vs in FIG. 3, this function f (k) is a curve that does not depend on Vs. Therefore, the function f (k) and the function of V / Vs are previously obtained by calculation using an equivalent circuit, or are obtained experimentally as the first table and stored in the ROM in the IC 12. Then, the value of the coupling coefficient k can be easily obtained from the values of V and Vs at each time with reference to the table. Also, the inverse function of f (k)
k = f ⁻¹ (V / Vs)
May be obtained as a theoretical expression or an approximate expression instead of a table, and may be included in the program in the IC 12.
[0013]
Another table or mathematical expression is prepared for the reader / writer IC 12. As the received power of the non-contact IC card, P0 is a received power at which the card operates stably and does not need to release excess heat. The received power P of the non-contact IC card is determined by the output voltage V of the amplifier 2 of the reader / writer device and the coupling coefficient k, and there is a function g given the relationship of (Equation 2).
P = g (Vs, k)
Call it. Therefore, [Equation 5]
P0 = g (Vs, k)
The relationship between Vs and k is obtained in advance and stored in the ROM in the IC 12 as the second table. It may also be represented by an approximate function instead of a table.
[0014]
The reader / writer IC 12 controls transmission power according to the flow shown in FIG. 4 using the first and second tables. In the figure, first, the set value of the output voltage Vs of the power control circuit 13 is initialized (step 41). The initial value at this time may be determined appropriately. For example, the Vs value when k = 0.05 in (Expression 4) is used. Next, a control signal is output to the power control circuit 13 so that the output voltage becomes the initialized set value Vs (step 42), and control timing is awaited (step 43). At the control timing, the output signal of the voltage detection circuit 11 is taken in to obtain the output voltage V of the amplifier 2 (step 44), and then the coupling coefficient k for V / Vs is obtained from the first table (step 45). Then, the value of Vs for the obtained coupling coefficient k is obtained from the second table (step 46), and control is returned to step 42 so that the output voltage of the power control circuit 13 becomes the obtained Vs.
[0015]
By repeating the above cycle, the received power of the non-contact IC card is controlled so as to be almost always the set value P0, so that damage to the non-contact IC card circuit due to heat generation or overvoltage can be surely prevented and stable operation can be achieved. Can be realized. The cycle of the control cycle in FIG. 4 is only required to follow the change in the coupling coefficient when the non-contact IC card is carried by a person and can be set to about 20 msec, for example, to the CPU of the IC 12. The overhead of the system may be slight and will not interfere with other operations.
[0016]
FIG. 5 is a block diagram showing another configuration example of the reader / writer device according to the present invention. The difference from the configuration of FIG. 1 is that a current detection circuit 14 is provided instead of the voltage detection circuit 11 of FIG. That is. In this configuration example, the current detection circuit 14 detects the output current I of the amplifier 2 and outputs a current signal. The relationship between the coupling degree k of the two antennas and the output current I of the amplifier 2 is a power control circuit. When the 13 output voltage Vs is obtained as a parameter, it is as shown in FIG. This relationship is also the result of simulation using the equivalent circuit of FIG. 2 and giving the same circuit constants as in FIG.
[0017]
As seen in FIG. 5, the output current I monotonously decreases with an increase in the coupling coefficient k of both antennas. If the power control circuit output voltage Vs and the output current I are known, the coupling coefficient k is uniquely determined. The output current I is proportional to the voltage Vs as in the case of FIG.
[Formula 6]
I = Vs · h (k)
Therefore, in this case, unlike the case of FIG. 1, if the relationship between I / Vs and h (k) is prepared as a table (referred to as the third table) instead of the first table, the detected values of Vs and I can be used. A coupling coefficient k is determined. Then, since the voltage Vs for applying the appropriate received power P0 to the contactless IC card with respect to the obtained k is obtained from the relationship of the second table (Equation 4), the same control as in FIG. 1 is possible. A control flow in the IC 12 at this time is shown in FIG. In this step, the voltage I is changed to the voltage V in step 74 to obtain the current I, and the table referred to in step 75 is the third table described above, and the other parts are the same as those in FIG. Needless to say, an approximate function may be used in place of the table in either FIG. 4 or FIG.
[0018]
As described above, it is possible to prevent damage due to excessive heat generation and overvoltage in the non-contact IC card. However, in controlling the output power for that purpose, there is some margin for the required power in the non-contact IC card. Even if there is a control error, the operation of the non-contact IC card is surely guaranteed. Therefore, some excessive heat generation in the regulator 4 is unavoidable, and there is also heat generation from each circuit due to normal operation. For this reason, when the non-contact IC card is left in the operating range for a long time, the output signal of the voltage detection circuit 11 or the current detection circuit 14 is monitored by the IC 12 and the change ΔV or ΔI exceeds a predetermined value. When the timer is started and then the set time of the timer is exceeded and the detected value V or I does not change more than a predetermined value, it is determined that the non-contact IC card is left in the operating range and the power control circuit The output voltage Vs 13 is reduced to 0 or significantly. The timer may be realized by a built-in timer of the IC 12 or software, and the timer setting time may be set to a value, for example, about 10 times the time required for processing of a normal non-contact IC card. By incorporating such a mechanism, even when the non-contact IC card is left in the operating range, unnecessary power consumption can be prevented, and damage due to heat generation can be more reliably prevented.
[0019]
【The invention's effect】
According to the present invention, the contactless IC card can be reliably prevented from being damaged due to heat generation or overvoltage regardless of where it is in the operation range or left in the operation range for a long time.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of a reader / writer device according to the present invention.
FIG. 2 is an equivalent circuit of a power transmission system to a contactless IC card.
FIG. 3 is a diagram illustrating a relationship of an amplifier output voltage V with respect to a coupling coefficient k of an antenna of a reader / writer device and an antenna of a non-contact IC card.
4 is a flow of power control by the IC 12 of FIG.
FIG. 5 is a block diagram showing another configuration example of the reader / writer device according to the present invention.
FIG. 6 is a diagram illustrating a relationship of an amplifier output current I with respect to a coupling coefficient k of an antenna of a reader / writer device and an antenna of a non-contact IC card.
7 is a flow of power control by the IC 12 of FIG.
FIG. 8 is a diagram illustrating a configuration of a conventional reader / writer device.
[Explanation of symbols]
2 Amplifier 11 Voltage detection circuit 12 IC for reader / writer
13 Power control circuit 14 Current detection circuit

Claims (1)

A reader / writer device having a function of supplying electric power to the non-contact IC card by electromagnetic coupling of the antenna of the non-contact IC card and the antenna of the own device,
Power control means for controlling the high-frequency power supplied to the antenna of the device itself;
Detection means for detecting an input high-frequency voltage or current to the antenna of the device;
A coupling coefficient calculation means for obtaining a coupling coefficient between the antenna of the non-contact IC card and the antenna of its own device from the input high-frequency voltage or current detected by the means and the output voltage of the power control means;
Control means for controlling the output voltage of the power control means so that the received power of the non-contact IC card becomes a predetermined value from the coupling coefficient obtained by the means;
With
A non-contact IC comprising a second control means for reducing the output voltage of the power control means on condition that the high-frequency voltage or current detected by the detection means does not change for a predetermined time or more. Card reader / writer device.

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