Transponder in communication system

• US 20050134434A1
• Filed: 01/11/2005
• Published: 06/23/2005
• Est. Priority Date: 08/19/2002
• Status: Active Grant

• Current Assignee: Brother Kogyo Kabushiki Kaisha (Brother Industries Limited)
• Original Assignee: Brother Kogyo Kabushiki Kaisha (Brother Industries Limited)
• Inventors: Nagai, Takuya
• Granted Patent: US 7,528,699 B2
• Time in Patent Office: Days
• US Class Current: 340/10.100
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs

Abstract

A transponder of a communication system, which has a high modulation factor for stable communication, and wherein an impedance element in the form of a coil is connected to an antenna of the transponder, and a resistor and a switching element in the form of a diode a high-frequency wave of which is grounded are connected to the coil. The antenna is a monopole antenna having a low impedance, and the coil has an inductance of 10 nH. Application of an electric current of 100 mA to the diode causes a phase difference of 122 degrees and an amplitude ratio of 1.1 with respect to a phase when the electric current is not applied to the diode.

Claims

1. A transponder of a communication system wherein an interrogator transmits a main carrier, and the transponder receives said main carrier through an antenna, and effects a predetermined modulation of said main carrier by changing an impedance of a circuit connected to said antenna, as viewed from said antenna, to generate a reflected wave for responding to said interrogator, wherein an improvement comprises:

said circuit including a switching element operable to modulate said main carrier received by said antenna, and an impedance element connected to said switching element; and

said impedance element having an impedance determined so as to provide a predetermined difference between a phase of a total impedance which is a sum of an input impedance of said antenna and an impedance of said circuit, at a frequency of said main carrier, when said switching element is in an on state, and that when the switching element is in an off state.

2. The transponder according to claim 1, wherein an amount of an electric current to be applied to said switching element is determined such that an absolute value of the total impedance of the input impedance of said antenna and the impedance of said circuit at the frequency of said main carrier when the switching element is in the on state is substantially equal to that when the switching element is in the off state.

3. The transponder according to claim 1, wherein said antenna has an impedance including a resistance component which is smaller than a total reactance component of the total impedance of the input impedance of the antenna and the impedance of said circuit at the frequency of said main carrier.

4. The transponder according to claim 1, wherein the impedance of said impedance element is determined so as to provide a difference of 90 degrees or higher between the phase of the total impedance of the input impedance of the antenna and the impedance of said circuit at the frequency of the main carrier when the switching element is in the on state, and that when the switching element is in the off state.

5. The transponder according to claim 1, wherein the impedance of said impedance element is determined so as to maximize a difference between the phase of the total impedance of the input impedance of the antenna and the impedance of said circuit at the frequency of the main carrier when the switching element is in the on state, and that when the switching element is in the off state.

6. The transponder according to claim 1, wherein said switching element includes a diode, and an amount of an electric current to be applied to said impedance element and said diode is determined so as to provide a difference of 90 degrees or higher between the phase of the total impedance of the input impedance of said antenna and the impedance of said circuit at the frequency of the main carrier when the electric current is applied to said diode and that when the electric current is not applied to the diode.

7. The transponder according to claim 1, wherein said switching element includes a diode, and an amount of an electric current to be applied to said impedance element and said diode is determined so as to maximize a difference between the phase of the total impedance of the input impedance of said antenna and the impedance of said circuit at the frequency of the main carrier when the electric current is applied to said diode and that when the electric current is not applied to the diode.

8. The endpoint deice according to claim 1, wherein said switching element includes a transistor.

9. The transponder according to claim 1, wherein said switching element includes a field-effect transistor.

10. The transponder according to claim 1, wherein said impedance element includes a coil.

11. The transponder according to claim 1, wherein said impedance element includes a capacitive load.

12. The transponder according to claim 1, wherein said impedance element includes a distributed-constant circuit having a stub.

13. The transponder according to claim 1, wherein said impedance element includes a combination of a coil and a capacitive load.

14. A communication system including an interrogator operable to transmit a main carrier, and a plurality of transponders each of which is constructed according to claim 1.