JPH1174823A - Non-contact ic card system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain efficient demodulation by using phase change by providing a phase shifter between a carrier wave oscillator and a multiplier, and changing the phase of the carrier wave for operating multiplication. SOLUTION: A phase shifter 6 is inserted between a carrier wave oscillator 5 and a multiplier 7 of a reader/writer unit(RWU) of a non-contact IC card system. In a load switch system for changing a capacitor to be inserted in parallel into the coil antenna of the non-contact IC card, when the capacity of the capacitor is changed, parallel oscillation frequency with the coil antenna is deviated from the frequency of a carrier wave received for a power, and the amplitude and phase of a carrier wave transmitted from a coil antenna 1 of the RWU is changed. In this case, the amplitude difference is changed by changing the phase shift amounts of the phase shifter 6. That is, the phase shift amounts for obtaining the maximum amplitude difference value is set by the phase shifter 6 so that an efficient data demodulator can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contactless IC card system using a load switch system, and more particularly to an improvement of a data demodulation device in a reader / writer unit (hereinafter, referred to as RWU).

[0002]

2. Description of the Related Art There is no power supply in an IC card, and RWU
A non-contact IC card system has been developed in which electric power is transmitted from a (reader / writer unit) by electromagnetic induction or the like in a non-contact manner and an IC card is operated with the electric power. FIG. 5 shows the configuration of the RWU of this system, and FIG. 6 shows the configuration of the contactless IC card. From the RWU, the output of the carrier oscillator 5 is amplified by the power amplifier 3 via the modulator 4 and transmitted from the coil antenna 1 of the RWU. When the coil antenna of the non-contact IC card in FIG. 6 approaches the coil antenna 1 of the RWU, power is transmitted from the RWU by electromagnetic induction. The coil antenna of the non-contact IC card forms a parallel resonance circuit with the capacitor C, the resonance frequency is tuned to the frequency of the received carrier wave, and efficient reception is performed. The received power received by this parallel resonance circuit is rectified by a bridge rectifier to become a DC power supply, a pulsating current is smoothed by a smoothing capacitor, stabilized to a constant voltage by a regulator, and supplied to a control unit and a demodulator.

[0003] Data transmission is also performed between the RWU and the contactless IC card. In order to transmit data from the RWU to the contactless IC card, the output of the carrier oscillator 5 of the RWU that is transmitting power in FIG. 5 is amplitude-modulated by the modulator 4 according to the transmission data from the control unit 12. In a non-contact IC card, a modulation component is extracted from a power carrier received by a coil antenna and demodulated by a demodulator. The clock of the transmission data is extracted by a clock extraction circuit. On the other hand, a load switch method is often used for transmitting data from a non-contact IC card. In the load switch system, when power is received by a coil antenna of a non-contact IC card, the reception impedance is changed by data to be transmitted, and the RWU detects a change in the transmission output amplitude of the transmitted power carrier. It is a method. For example, the control unit in FIG. 6 does nothing when transmitting data “1”, but connects a switch when transmitting data “0”, and further connects the switch to a capacitor C connected in parallel to the coil antenna. , A series circuit of capacitors C1 and C2 is added. When the series circuit of the capacitors C1 and C2 is added in parallel, the resonance frequency of the receiving coil antenna of the non-contact IC card changes, so that the receiving impedance for receiving power changes and the coil antenna on the RWU side electromagnetically coupled. 1 changes. As a result, the transmission voltage value of the power amplifier 3 changes, and the change is
, The data signal from the non-contact IC card can be received.

[0004] Data reception in the RWU is performed via a coupler 2 provided between the coil antenna 1 and the power amplifier 3. In order to demodulate a change in the amplitude of the transmission voltage of the power amplifier 3 due to a change in the load electromagnetically coupled to the coil antenna 1, an asynchronous detection method or a synchronous detection method is used, but the synchronous detection method is more preferable. Good detection efficiency. In a normal synchronous detection method, a carrier component is extracted from a received modulated wave by a PLL (phase lock loop) circuit or the like, and the modulated data signal component is extracted by multiplying the received modulated wave by a load modulation method. Then
Since the received modulated wave is a carrier from a carrier oscillator that transmits power, it is not necessary to newly extract a carrier component. That is, in FIG. 5, the transmission voltage whose amplitude has changed due to the load fluctuation is taken out by the coupler 2 and the output of the carrier oscillator 5 is multiplied by the multiplier 7. From the output of the multiplier 7, high-frequency components are removed by an LPF (low-pass filter) 8,
The data is amplified by the amplifier 9 and the data is determined by the comparator 10. The received data is waveform-shaped by the shaper 11 and the control unit 12
Received at.

[0005]

The data transmission from the non-contact IC card in the load switch system is performed by the non-contact IC card.
This is an extremely simple method because data can be transmitted from the C card without newly transmitting a carrier wave. However, the electromagnetic coupling between the RWU and the IC card is originally small, and only the reception impedance when receiving power is changed. Therefore, the modulation degree cannot be increased. That is, RW
It is difficult to give a large amplitude change to the carrier power output for U power. Therefore, data demodulation in the RWU has a difficulty in that the modulation factor is shallow. In particular, when the distance between the coil antenna 1 of the RWU and the coil antenna of the non-contact IC card is increased and the electromagnetic coupling is weakened, demodulation on the RWU side becomes extremely difficult.

An object of the present invention is to provide a data demodulation apparatus which can perform better data demodulation even when the modulation is shallow in data reception by the load switch system.

[0007]

SUMMARY OF THE INVENTION When data is transmitted from a non-contact IC card using a load switch method that changes the capacity of a capacitor inserted in parallel with a coil antenna of the non-contact IC card, a carrier wave of the RWU is used. In the output,
Focusing on the occurrence of amplitude change and phase change, demodulation by the RWU involves installing a phase shifter between the carrier oscillator and the multiplier, and changing the phase of the carrier to be multiplied to obtain the phase change. Use and perform efficient demodulation.

[0008]

Embodiments of the present invention will be described below in detail. FIG. 1 is a configuration diagram of the RWU of the contactless IC card system according to the present invention. This configuration differs from the configuration of the conventional RWU in FIG. 5 in that a phase shifter 6 is inserted between a carrier oscillator 5 and a multiplier 7.
Others are the same. Hereinafter, a data demodulation method in the system of the present invention will be described with reference to FIG.

As shown in FIG. 6, in the load switch system in which the capacitor inserted in parallel to the coil antenna of the non-contact IC card is changed, the parallel resonance frequency with the coil antenna is changed by changing the capacitance of the capacitor. And the amplitude and phase of the carrier transmitted from the coil antenna 1 of the RWU change. Assuming that the load-switch type modulated wave detected by the coupler 2 in FIG. 1 is e (t), e (t) is represented by the following equation.

E (t) = Ao (1 + m) cos (ωct + θ) where Ao is the amplitude of the carrier and ωc is the angular frequency of the carrier. m and θ are the amplitude change and phase change generated in the carrier when the capacitor is changed by the non-contact IC card,
When the transmission data is “1”, m = 0 and θ = 0, and when the transmission data is “0”, m = mo θ = θo. This modulated wave e (t) is input to the multiplier 7. Assuming that the output from the carrier oscillator 5 is cos ωct, a signal y (t) having passed through the phase shifter 6 and having a phase shifted by φ is given by y (t) = cos (ω
ct + φ). When y (t) is multiplied by e (t) by the multiplier 7, the following equation is obtained.

[Equation 2] e (t) × y (t) = Ao (1 + m) cos (ωct + θ) × cos (ωct +
φ) = ｛Ao (1 + m) / 2｝ × ｛cos (2ωct + θ + φ) + cos (θ-
When the component of φ) 成分 2ωc is removed by the LPF (low-pass filter) 8, L
Demodulated output data b (t), which is the output of PF8, is given by the following equation.

[Mathematical formula-see original document] b (t) = {Ao (1 + m) / 2} × cos (θ-φ) As output data, the output amplitude when data is “1” and the output amplitude when data is “0” Is large, the comparator 10 can easily detect the difference. Therefore, when the above output amplitude difference D is obtained, the following equation is obtained.

D = (Ao / 2) × cos (−φ) − {Ao (1 + mo) / 2} × cos (θo−φ) As is clear from this equation, the phase shift of the phase shifter 6 is obtained. It can be seen that changing the amount φ changes the amplitude difference D. That is, if the phase shift amount φ at which the maximum value of D is obtained is set by the phase shifter 6, an efficient data demodulator can be obtained.

Hereinafter, a specific value will be calculated using (Equation 4). It is assumed that carrier amplitude Ao = 2 in (Equation 4).
The values of mo and θo are Q of the parallel resonance circuit formed by the capacitor C in parallel with the coil antenna of the contactless IC card of FIG.
It is determined by the values of the capacitors C1 and C2 inserted in parallel. Assuming that mo = −0.1, the output amplitude difference D is given by the following equation.

D = cos (φ) −0.9 cos (θo−φ) The difference D between the amplitude when the data is “1” and the output amplitude when the data is “0” is the data output at the input of the comparator 10. Since this value corresponds to the amplitude, if the value is large, it becomes easy for the comparator 10 to distinguish between data “1” and data “0”. Therefore, the value of D in (Equation 5) is calculated as follows.
In the case of ° and 0 °, calculation is performed by changing φ, as shown in FIGS. 2, 3, and 4. First, θo in FIG.
In the case of °, when the phase shift amount φ in the phase shifter 6 is changed from 0 ° to 360 °, the output amplitude difference D changes as shown in the figure. The maximum value is 1.345 when the phase shift amount is 318 °. On the other hand, when the phase is not shifted by the phase shifter 6, that is, when φ = 0 ° as in the conventional method, the output amplitude difference D is 1 from FIG. Accordingly, it is shown that when the phase is shifted by 318 ° by the phase shifter 6, the output amplitude difference D can be increased to 1.345 times.

FIG. 3 shows a case where θo is 30 °. When the phase shift amount φ in the phase shifter 6 is changed from 0 ° to 360 ° as in FIG. 2, the maximum value of the output amplitude difference D is obtained when the phase shift amount is 296 °.
It turns out that it is 0.501. Since the output amplitude difference D when the phase shift amount φ is 0 ° is 0.22, an output amplitude difference of twice or more is obtained. FIG. 4 shows the case where θo is 0 °. This means that there is no phase change. In this case, the maximum output amplitude difference D is obtained when the phase shift amount φ in the phase shifter 6 is also 0 °.
Is obtained, but the value is very small as 0.1.

From the results shown in FIGS. 2, 3, and 4, when the carrier has only an amplitude change in the load switch method,
Although the use of the method of the present invention has no effect, it can be seen that the present invention has a remarkable effect when a phase change accompanies an amplitude change. Non-contact I as shown in FIG.
In the case of using a load switch method in which the value of a capacitor inserted in parallel with a coil antenna is changed for data transmission by the C card, both the amplitude change and the phase change are present in the carrier wave. The method is very effective.

[0013]

According to the present invention, a demodulated output amplitude greater than the amplitude change in amplitude modulation can be obtained, and the following effects are obtained. (1) Good reception can be performed even if the C / N ratio of the coil antenna of the RWU is small. (2) Even if the distance between the RWU and the non-contact IC card is long, data can be transmitted, so that the service area of the non-contact IC card can be widened.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a reader / writer unit of a non-contact IC card system according to the present invention.

FIG. 2 shows that the phase of a carrier wave is changed from 0 ° to 36 when θ is 90 °.
FIG. 11 is a diagram illustrating an output amplitude difference of data when the phase is shifted to 0 °.

FIG. 3 shows that the phase of the carrier wave is changed from 0 ° to 36 when θ is 30 °.
FIG. 11 is a diagram illustrating an output amplitude difference of data when the phase is shifted to 0 °.

FIG. 4 shows that the phase of the carrier wave is changed from 0 ° to 36 when θ is 0 °.
FIG. 11 is a diagram illustrating an output amplitude difference of data when the phase is shifted to 0 °.

FIG. 5 is a configuration diagram of a conventional reader / writer unit.

FIG. 6 is a configuration diagram of a non-contact IC card.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 RWU coil antenna 2 Coupler 3 Power amplifier 4 Modulator 5 Carrier oscillator 6 Phase shifter 7 Multiplier 8 LPF (low-pass filter) 9 Amplifier 10 Comparator 11 Shaper

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsuhiro Okada 3- 14-20 Higashinakano, Nakano-ku, Tokyo Kokusai Electric Co., Ltd. (72) Keisuke Igarashi 3-14-20 Higashinakano, Nakano-ku, Tokyo Kokusai Electric Inside the corporation

Claims (1)

[Claims] 1. A reader / writer unit and a non-contact IC supplied with electric power by electromagnetic coupling from the reader / writer unit
A non-contact IC card system comprising a card. In the non-contact IC card, the antenna load is varied according to transmission data so that at least a phase change occurs in a change in load as viewed from a reader / writer unit. The reader / writer unit is configured to generate a local carrier for detecting a carrier supplied to the antenna from a carrier oscillator output of the reader / writer unit via a phase shifter. Contact IC card system.