Registers – Records – Conductive
Reexamination Certificate
1999-02-02
2001-02-27
Lee, Michael G (Department: 2876)
Registers
Records
Conductive
C235S487000, C340S010200, C340S870030
Reexamination Certificate
active
06193164
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an IC card and an IC card system and, more particularly, to an IC card which transmits in a non-contact manner a signal modulated with desired data and to an IC card system using the IC card.
2. Description of the Related Art
IC card systems using IC cards have been applied to ticket examination systems for use in transport facilities, room entry/exit control systems, etc. An IC card system of this kind has been proposed which is constituted of IC cards carried by users and a read/writer (i.e., IC card processor) for exchanging various sorts of data with each of the IC cards. Various sorts of data are transmitted and received between the IC card and the read/writer in a non-contact manner.
That is, in this kind of IC card system, the read/writer forms a transmission signal by modulating a carrier having a predetermined frequency with a desired data sequence, and sends out the transmission signal to the IC card via an antenna.
The IC card receives the transmission signal via an antenna and demodulates the transmission signal to reproduce the data sent from the read/writer. Further, the IC card sends out data such as personal information stored therein to the read/writer in response to the received data by modulating a predetermined carrier with the data to be transmitted.
The read/writer receives the data sent from the IC card, and opens or closes a door of a ticket examination machine or allows entry into or exit from a room.
A type of IC card for such use has been proposed which is arranged to send out desired data to a read/writer by the method of changing the power radiated from the antenna by changing the load impedance of the antenna (hereinafter referred to as “load switching system”).
That is, in the antenna of the IC card, a transmission signal sent from the read/writer is induced and this transmission signal is reradiated. If at this time the load impedance of the antenna is changed, the reradiated power is correspondingly changed. Then, in the receiving antenna coupled to the antenna of the IC card, the carrier of the transmission signal is detected at the signal level corresponding to the change in the load impedance.
In such a load switching system, desired data can be sent out by being modulated in an amplitude shift keying (ASK) manner based on a simple arrangement. The overall configuration can be correspondingly simplified.
This kind of IC card is carried by a user and is brought close to the read/writer when used. Therefore, the signal level of the transmitted signal induced in the antenna varies largely depending upon use.
In the load switching system, therefore, there is a need to use a semiconductor device having a sufficiently high withstand voltage as a semiconductor device for changing the load impedance of the antenna to ensure the desired operation even when the signal level varies largely as described above. If a semiconductor device having such a sufficiently high withstand voltage is used, it is difficult to integrate the entire circuit of the IC card to the desired degree of integration.
As a solution for this problem, a method of processing the signal obtained from the antenna by clamping the signal may be used. If such a method is used, the power reradiated by following the change in the load impedance cannot be sufficiently changed. That is, the degree of amplitude shift keying modulation is reduced, resulting in a deterioration in data quality.
SUMMARY OF THE INVENTION
In view of these circumstances, an object of the present invention to provide an IC card and an IC card system capable of performing data exchange without a semiconductor device having a sufficiently large withstand voltage while being arranged as simply as the load switching system.
To achieve the above-described object, according to one aspect of the present invention, there is provided an IC card in which a reference signal having the same frequency as a carrier of a transmission signal received by an antenna and phase-synchronized with the carrier is formed, and in which a response data sequence is sent out from the antenna by modulating the reference signal with the response data sequence in a phase shift keying (PSK) manner.
According to another aspect of the present invention, there is provided an IC card in which the load on a power supply circuit for producing operating power by rectifying a transmission signal received by an antenna is changed according to a response data sequence.
According to still another aspect of the present invention, there is provided an IC card system constituted of each of the above-described IC cards.
According to a further aspect of the present invention, there is provided an IC card in which a reference signal having the same frequency as a carrier of a transmission signal received by an antenna and phase-synchronized with the carrier is formed, and in which the reference signal is selectively sent out from the antenna according to a response data sequence.
If, in an IC card, a reference signal having the same frequency as a carrier of a transmission signal received by an antenna and phase-synchronized with the carrier is formed, and if a response data sequence is sent out from the antenna by PSK-modulating the reference signal with the response data sequence, a reference signal can be stably formed by performing amplitude limitation of an input to a reference signal forming circuit for forming the reference signal, or by a like method, thereby sending out a response signal. In this manner, data exchange can be performed by a system arranged as simply as the load switching system without using a semiconductor device having a high withstand voltage.
If, in an IC card, the load on a power supply circuit for producing operating power by rectifying a transmission signal received by an antenna is changed according to a response data sequence, a response signal can be sent out with the same effect as in the case of changing the load impedance of the antenna. At this time, even if an excessively large transmission signal is received, the operation of exchanging data can be stably performed by clamping the output from the power supply circuit or by a like method. In this manner, data exchange can be performed by a system arranged as simply as the load switching system without using a semiconductor device having a sufficiently high withstand voltage.
Each of the thus-arranged IC cards can form an IC card system having a simple configuration.
An IC card may also be arranged in which a reference signal having the same frequency as a carrier of a transmission signal received by an antenna and phase-synchronized with the carrier is formed, and in which the reference signal is selectively sent out from the antenna according to a response data sequence, thereby enabling a system arranged as simply as the load switching system to perform data exchange without using a semiconductor device having a high withstand voltage.
REFERENCES:
patent: 4546241 (1985-10-01), Walton
patent: 4691202 (1987-09-01), Denne et al.
patent: 4963887 (1990-10-01), Kawashima et al.
patent: 5418353 (1995-05-01), Katayama et al.
patent: 5426423 (1995-06-01), Raimbault et al.
patent: 5517194 (1996-05-01), Carroll et al.
patent: 0 677 815 A2 (1995-03-01), None
Cyr Daniel St.
Lee Michael G
Limbach & Limbach L.L.P.
Sony Corporation
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