Non-contact communication system

• US 6,731,199 B1
• Filed: 07/26/1999
• Issued: 05/04/2004
• Est. Priority Date: 07/27/1998
• Status: Expired due to Term

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Ueda, Takashi
• Primary Examiner(s): Zimmerman, Brian
• Assistant Examiner(s): YANG, CLARA I
• Application Number:
  US09/359,651
• Time in Patent Office: 1,744 Days
• Field of Search: 340/10.1, 340/10.3, 340/10.4, 340/825, 340/572.2, 340/10.34, 340/572.1, 340/572.4, 235/380
• US Class Current: 340/10.4
• CPC Class Codes: G06K 19/0701 at least one of the integrated circuit chips comprising an arrangement for power management
• CPC Class Codes: G06K 19/0715 the arrangement including means to regulate power transfer to the integrated circuit
• CPC Class Codes: H04B 1/04 Circuits
• CPC Class Codes: H04B 2001/0416 having gain or transmission power control

Abstract

In a non-contact communication system, when an interrogator is attempting to detect that a responder is present in a range communicable therewith, the interrogator transmits a weak radio wave from its tuning circuit. The responder receives this radio wave and acquires electric power by rectifying it, but, because the electric power thus obtained is insufficient, the responder is turned on and off repeatedly at regular intervals. This causes variation in the impedance with which the tuning circuit is loaded. The interrogator, by detecting this variation in the impedance occurring at regular intervals, recognizes that the responder is present within the range communicable therewith. Only then, the interrogator transmits a radio wave strong enough to permit the responder to acquire sufficient electric power.

Claims

1. A non-contact communication system comprising:

a first communication unit for selectively radiating through a common tuning circuit thereof one of a radio wave for communication and a radio wave for detection, the radio wave for communication having alternately a period in which the radio wave is not modulated and a period in which the radio wave is modulated in accordance with data to be transmitted, the radio wave for detection having a smaller amplitude than the radio wave for communication and comprising only a carrier without including the data to be transmitted and data to be received; and

a second communication unit for communicating with the first communication unit by modulating the radio wave for communication in accordance with reply data during said period in which the radio wave is not modulated,

wherein the first communication unit generates a radio wave for detection;

the second communication unit causes a frequency different from a frequency of the radio wave for detection to be superimposed on the radio wave for detection because an impedance with which the tuning circuit of the first communication unit is loaded when the second communication unit repeatedly switches between an operative state during which the second communication unit obtains power for functioning by tuning in to the radio wave for detection and a non-operative state during which the second communication unit obtains no power for functioning by detuning in to the radio wave for detection, and

the first communication unit, by detecting said frequency which is different from the frequency of the radio wave for detection and superimposed on the radio wave for detection, recognizes that the second communication unit is present within a range communicable with the first communication unit and then starts transmitting the radio wave for communication.

2. A non-contact communication system as claimed in claim 1, wherein the first communication unit has:

a frequency detecting means for detecting the frequency superimposed on the radio wave transmitted from the first communication unit, the frequency resulting from repeated switching between an activation period in which the second communication unit is activated by power of the radio wave for detection and a deactivation period in which the second communication unit is deactivated because of insufficient power of the radio wave for detection because the radio wave for detection transmitted from the first communication unit is so feeble as to be equal to critical strength that divides between activation and deactivation of the second communication unit when the second communication unit is present within the range communicable with the first communication unit;

a checking means for checking whether the second communication unit is present within the range communicable with the first communication unit or not on a basis of an output from the frequency detecting means; and

a control means for controlling the first communication unit to transmit the radio wave for communication on a basis of an output from the checking means.

3. A non-contact communication system as claimed in claim 1,

wherein the second communication unit has a signal generating means for generating a reply data signal by changing an internal impedance thereof according to the reply data and changing an amplitude of the radio wave for communication when the second communication unit catches the radio wave for communication transmitted from the first communication unit so as to make the first communication unit recognize that the second communication unit is present within the range communicable with the first communication unit.

4. A non-contact communication system as claimed in claim 1,

wherein the first communication unit transmits alternatively the radio wave for communication or the radio wave for detection, both of which are different only in an amplitude thereof, by using a single transmission means shared between those two radio waves.

5. A non-contact communication system as claimed in claim 4,

wherein the first communication unit has:

a frequency detecting means for detecting the frequency superimposed on the radio wave transmitted from the first communication unit, the frequency resulting from repeated switching between an activation period in which the second communication unit is activated by power of the radio wave for detection and a deactivation period in which the second communication unit is deactivated because of insufficient power of the radio wave for detection because the radio wave for detection transmitted from the first communication unit is so feeble as to be equal to critical strength that divides between activation and deactivation of the second communication unit when the second communication unit is present within the range communicable with the first communication unit;

a checking means for checking whether the second communication unit is present within the range communicable with the first communication unit or not on a basis of an output from the frequency detecting means; and

a control means for controlling the first communication unit to transmit the radio wave for communication on a basis of an output from the checking means.

6. A non-contact communication system as claimed in claim 4,

wherein the second communication unit has a signal generating means for generating the reply data signal by changing an internal impedance thereof according to a the reply data and changing an amplitude of the radio wave for communication when the second communication unit catches the radio wave for communication transmitted from the first communication unit so as to make the first communication unit recognize that the second communication unit is present within the range communicable with the first communication unit.

7. A non-contact communication system comprising:

a first communication unit for selectively radiating through a common tuning circuit thereof one of a radio wave for communication and a radio wave for detection, the radio wave for communication having alternately a period in which the radio wave is not modulated and a period in which the radio wave is modulated in accordance with data to be transmitted, the radio wave for detection having a smaller amplitude than the radio wave for communication and comprising only a carrier without including the data to be transmitted and data to be received; and

a second communication unit having a resonant circuit and operating on electric power generated in the resonant circuit,

wherein, when the first communication unit transmits the radio wave for detection and the second communication unit is within a range communicable with the first communication unit, a cyclical state change, occurs in the second communication unit; and

the cyclical state change consisting of an increase of the electric power higher than a predetermined value by which the second communication unit is activated, a loading of the resonant circuit, a decrease in an impedance thereof below a predetermined level, a decrease of the electric power lower than the predetermined value, an unloading of the resonant circuit, and an increase in the impedance thereof higher than the predetermined level, causes an impedance with which the common a tuning circuit of the first communication unit is loaded to fluctuate at a predetermined frequency different from a frequency of the radio wave for detection, a

wherein the first communication unit transmits the radio wave for communication after having sensed a presence of the second communication unit by detecting the fluctuations of the impedance with which the tuning circuit of the first communication unit is loaded.