RFID reader
First Claim
1. An RFID tag reader, the reader comprising:
- an electromagnetic (EM) field generator having a resonant circuit for generating an electromagnetic (EM) field for modulation by said tag, said modulation comprising modulating load of said EM field by said tag, the resonant circuit arranged such that current in the resonant circuit is responsive to said load modulation;
a detector system responsive to fluctuations in strength of said EM field at said reader;
a demodulator responsive to said detector system to demodulate said EM field modulation by said tag;
a stimulus circuit for exciting resonance of the resonant circuit, the stimulus circuit comprising a switch circuit having a coupling to the EM field generator; and
a rectified power supply output for powering the EM field generator, the power supply output coupled to a capacitor and to the switch circuit,wherein the switch circuit is coupled to, when the stimulus circuit is controlled to excite the resonance, pass charge from the EM generator to charge the capacitor until voltage on the capacitor reaches voltage on the EM field generator and then pass charge from the power supply to the EM field generator, wherein an increase in said load reduces a duration of said charging said capacitor and increases a duration of said passing charge to the EM field generator to compensate for variations in amplitude of resonance of the resonant circuit with variation of power delivered to the resonant circuit by the power supply.
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Accused Products
Abstract
Embodiments of the invention relate to the field of RFID (radio frequency identification). Some particularly preferred embodiments relate to a high-Q, so-called “full duplex” (FDX) RFID Reader. An RFID tag reader, the reader comprising: an electromagnetic (EM) field generator for generating an electromagnetic (EM) field for modulation by said tag, said modulation comprising modulated load of said EM field by said tag; a detector system responsive to fluctuations in strength of said EM field at said reader; a negative feedback system responsive to said detector system to provide a control signal for said EM field generator for controlling said EM field generator to reduce said detected fluctuations; and a demodulator responsive to said control of said EM field to demodulate said EM field modulation by said tag.
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Citations
19 Claims
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1. An RFID tag reader, the reader comprising:
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an electromagnetic (EM) field generator having a resonant circuit for generating an electromagnetic (EM) field for modulation by said tag, said modulation comprising modulating load of said EM field by said tag, the resonant circuit arranged such that current in the resonant circuit is responsive to said load modulation; a detector system responsive to fluctuations in strength of said EM field at said reader; a demodulator responsive to said detector system to demodulate said EM field modulation by said tag; a stimulus circuit for exciting resonance of the resonant circuit, the stimulus circuit comprising a switch circuit having a coupling to the EM field generator; and a rectified power supply output for powering the EM field generator, the power supply output coupled to a capacitor and to the switch circuit, wherein the switch circuit is coupled to, when the stimulus circuit is controlled to excite the resonance, pass charge from the EM generator to charge the capacitor until voltage on the capacitor reaches voltage on the EM field generator and then pass charge from the power supply to the EM field generator, wherein an increase in said load reduces a duration of said charging said capacitor and increases a duration of said passing charge to the EM field generator to compensate for variations in amplitude of resonance of the resonant circuit with variation of power delivered to the resonant circuit by the power supply. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of remotely interrogating a transponder, the method comprising:
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powering an electromagnetic (EM) field generator from a rectified power supply output having an output capacitor, the EM field generator comprising a resonant circuit; generating, using the EM field generator, an electromagnetic (EM) field for modulation by said transponder, said modulation comprising modulating load of said EM field by said transponder, wherein current in the resonant circuit is responsive to said load modulation stimulating the resonant circuit by controlling a switch circuit coupled to the EM field generator and the rectified power supply output; and demodulating said modulation of said EM field by said transponder, wherein the stimulating comprises, when the switch circuit is controlled to excite the resonant circuit, the switch circuit passing charge from the EM field generator to charge the output capacitor until voltage on the output capacitor reaches voltage on the EM field generator and the switch circuit then passing charge from the power supply output to the EM field generator, wherein an increase in said load reduces a duration of said charging said output capacitor and increases a duration of said passing charge to the EM field generator, to compensate for variations in amplitude of resonance of the resonant circuit with variation of power delivered to the resonant circuit by the power supply output.
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19. Apparatus for remotely interrogating a transponder, the apparatus comprising:
- means for generating an electromagnetic (EM) field for modulation by said transponder, said modulation comprising load absorption of said EM field by said transponder, the means comprising a resonant circuit such that current in the resonant circuit is responsive to said load modulation;
means for powering the means for generating the EM field, the means for powering comprising a rectified power supply output having an output capacitor; means for stimulating the resonant circuit by controlling a switch circuit coupled to the means for generating an EM field and the rectified power supply output; and means for demodulating said modulation of said EM field by said transponder, wherein the means for stimulating is such that, when the switch circuit is controlled to excite the resonant circuit, the switch circuit passes charge from the means for generating an EM field to charge the output capacitor until voltage on the output capacitor reaches voltage on the means for generating an EM field and the switch circuit then passes charge from the power supply output to the means for generating an EM field, wherein an increase in said load reduces a duration of said charging said output capacitor and increases a duration of said passing charge to the means for generating an EM field, to compensate for variations in amplitude of resonance of the resonant circuit with variation of power delivered to the resonant circuit by the power supply output.
- means for generating an electromagnetic (EM) field for modulation by said transponder, said modulation comprising load absorption of said EM field by said transponder, the means comprising a resonant circuit such that current in the resonant circuit is responsive to said load modulation;
Specification