Telecommunications – Transmitter and receiver at separate stations – Short range rf communication
Reexamination Certificate
1997-09-15
2001-11-20
Maung, Nay (Department: 2681)
Telecommunications
Transmitter and receiver at separate stations
Short range rf communication
C455S343200, C455S106000
Reexamination Certificate
active
06321067
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a power transmission system, an IC card and an information communication system using an IC card, wherein commutation tickets, railway tickets, bus tickets, etc. to be used at wickets in railway stations or on buses will be replaced with IC cards, and when an IC card is made to pass a reader/writer, being provided at a wicket in a railway station or on a bus, with noncontact or in close proximity to it, power can be transmitted from the reader/writer to the IC card by radio.
It has been known that power can be supplied to an IC card from a power supply side by a noncontact method using rays of light or magnetic fields.
When commutation tickets, railway tickets, bus tickets, etc. to be used at wickets in railway stations or on buses will be replaced with IC cards, and when a user passes an IC card through a reader/writer provided at a wicket in a railway station or on a bus with noncontact, the distance between the IC card and the reader/writer may vary much. When the reader/writer is so adjusted that proper power can be transmitted from the reader/writer to the IC card when the distance between the IC card and the reader/writer is comparatively large, then in a case where the distance between the reader/writer and the IC card is small, excessive power may be transmitted from the reader/ writer to the IC card, which may cause a malfunction or breakage of the IC card.
In other words, in the prior art, careful consideration was not given to a point that proper power shall be stably transmitted to an IC card from a reader/ writer even though the distance between the IC card and the reader/writer may be largely varied.
Prior art in which it is intended to stably supply power from a reader/writer to an IC card even if the distance between the IC card and the reader/writer is largely varied is explained in Japanese Patents Laid-open No. Hei 7-85233 and Laid-open No. 9-62816.
In the Japanese Patent Laid-open No. 7-85233, following are described: among noncontact type data carriers of electromagnetic coupling system, in the case of movable equipment having a function to be able to receive data including a control signal from fixed equipment, a rectifier circuit composed of a rectifier D
1
and a capacitor C
2
, and a variable resistor element composed of a transistor T
2
, resistor R
3
and resistor R
4
being controlled by a DC voltage obtained from the rectifier circuit are connected to a receiving coil of the data carrier in parallel, and an excess power will be consumed in the variable resistor elements. Further it is described in the Japanese Patent Laid-open No. Hei 7-85233 that a signal detector circuit composed of a rectifier D
2
, a resistor R
1
and a capacitor C
3
which detects an amplitude-modulated wave superimposed on a AC voltage induced in the receiving coil and transmits the detected data to a main circuit of the data carrier as an input signal, and an amplitude modulator circuit which receives the output signal of the main circuit of the data carrier for switching a transistor T
1
, and being composed of the transistor T
1
which transmits data from the data carrier to the fixed equipment, a capacitor C
4
and a resistor R
2
are connected to the receiving coil of the data carrier in parallel. In the prior art as mentioned in the above, a resonant circuit is not formed in the receiving coil of the data carrier, so that in a case where the distance between the transmitting coil on the fixed side and the receiving coil on the data carrier side is large, an enough voltage is not induced in the receiving coil and it is made difficult to obtain the power required by the main circuit of the data carrier. There is also another problem in the prior art. Since a half-wave rectifier is adopted in the prior art, a large ripple is produced, which requires a large smoothing capacity; therefore, it is made difficult to incorporate a capacitor of a large capacity in a data carrier in miniaturizing it.
It is described in the Japanese Patent Laid-open No. Hei 9-62816 that a receiving signal level of a resonance circuit of an antenna for transmitting and receiving data is detected and the quality factor Q of the antenna resonance circuit is varied by changing the variable resistor element according to the detected voltage in order to adjust a receiving signal level to a desirable value.
In these prior art, since a variable resistor element is directly connected to a receiving antenna in parallel, there is a problem in that the temperature rise in the variable resistor element is large and the size of a pressure protection circuit becomes large.
SUMMARY OF THE INVENTION
The purpose of the present invention is to solve the above-mentioned problems and offer an IC card and a power transmission system by radio in which it is made possible to stably supply power by radio from a reader/ writer to the internal circuit of an IC card in miniaturizing the elements of a pressure protection circuit and decreasing the temperature rise in a variable impedance circuit provided in an IC card even though the distance between the IC card and the reader/writer may be largely varied.
Another object of the present invention is to offer an IC card and a power transmission system by radio in which the power can be stably supplied to the internal circuit of the IC card by radio from a reader and/or writer by only making the IC card pass the reader and/or writer with noncontact or in close proximity to it by improving the responsibility of the system in miniaturizing the elements in a pressure protection circuit and decreasing the temperature rise in a variable impedance circuit.
A further object of the present invention is to offer an IC card and an information communication system using an IC card in which it is made possible to supply power stably from a reader and/or writer to the IC card with noncontact in miniaturizing the elements in the pressure protection circuit and decreasing the temperature rise in the variable impedance circuit provided in the IC card and to perform information communication with high reliability between the reader and/or writer and the IC card.
Yet another object of the present invention is to offer a power transmission system by radio, an IC card and an information communication system using the IC card. In the power transmission system by radio it is so arranged that power can be stably supplied even when the distance between an IC card and a reader/writer is largely varied in decreasing the temperature rise in the variable impedance circuit by controlling the static capacity for the induced power received on the IC card side.
A still further object of the present invention is to offer a power transmission system by radio, an IC card and an information communication system using the IC card. In the power transmission system by radio it is so arranged that proper power can be stably supplied to the IC card by radio from the power transmission portion of the reader/writer by only passing the IC card through the reader/writer with noncontact or in proximity to it and information can be communicated between the reader/writer and the IC card with high reliability.
In order to achieve the above-mentioned objects, the present invention is a power transmission system in which power is transmitted by radio from a power transmitting device (reader and/or writer device) to an IC card. The IC card comprises: an antenna having a resonance circuit for receiving the transmitted radio wave, a full wave rectifier circuit for rectifying an induced power received by the antenna, a power supply circuit which converts a DC voltage output from the full wave rectifier circuit into a power supply voltage, a detector circuit which detects the DC voltage output from the full wave rectifier circuit, an impedance control circuit portion which produces a desired power supply voltage from the DC voltage detected in the detector circuit by controlling the impedance of the circuit, and an internal circuit to be supplied with the desired power supp
Hayashi Yoshihiko
Nagai Kenji
Suga Takashi
Yoshino Ryouzou
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Maung Nay
Trinh Sonny
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