Cloaking circuit for use in a radiofrequency identification and method of cloaking RFID tags to increase interrogation reliability
First Claim
1. An improvement in an RFID tag passively powered through an antenna comprising:
- a series switch coupled between said antenna and said RFID tag; and
a time-delay circuit coupled to and controlling said series switch to activate said series switch to disconnect said RFID tag from said antenna for a predetermined time delay, said timed-delay circuit being activated upon a logic command, CLOAK, generated by said RFID tag, so that said antenna is provided during said predetermined time period with a high antenna load, thereby reducing the effective absorption and scattering aperture of said antenna during said predetermined time period.
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Accused Products
Abstract
The antenna of an RFID tag or label is disconnected from the balance of the RFID chip by means of a series switch activated in response to a logic command, CLOAK, generated by the RFID chip. Activation of the switch disconnects the antenna of the RFID tag for the remainder of the RFID chip and effects a high impedance resistance across the antenna terminals. An RC circuit is charged by activation of the CLOAK signal and thereafter discharges during a predetermined RC time period as determined by a high impedance series antifuse leakage transistor. The antenna is thus disconnected for a time sufficient to allow the remaining RFID tags in an RF interrogation field to be identified. Meanwhile, during the disconnection of the antenna from the RFID chip and its loading causes its effective absorption and scattering aperture to be reduced near zero so as to electromagnetically remove the RFID tag from the zone of interrogation during the predetermined time period. Hence, the interrogated tag remains disconnected and noninterferring with the RF field used to interrogate the remaining tags.
198 Citations
18 Claims
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1. An improvement in an RFID tag passively powered through an antenna comprising:
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a series switch coupled between said antenna and said RFID tag; and a time-delay circuit coupled to and controlling said series switch to activate said series switch to disconnect said RFID tag from said antenna for a predetermined time delay, said timed-delay circuit being activated upon a logic command, CLOAK, generated by said RFID tag, so that said antenna is provided during said predetermined time period with a high antenna load, thereby reducing the effective absorption and scattering aperture of said antenna during said predetermined time period. - View Dependent Claims (2, 4, 5, 6, 7, 8)
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3. An improvement in an RFID tag passively powered through an antenna comprising:
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a series switch coupled between said antenna and said RFID tag; and a time-delay circuit coupled to and controlling said series switch to activate said series switch to disconnect said RFID tag from said antenna for a predetermined time delay, said timed-delay circuit being activated upon a logic command, CLOAK, generated by said RFID tag, so that said antenna is provided during said predetermined time period with a high antenna load, thereby reducing the effective absorption and scattering aperture of said antenna during said predetermined time period; wherein said time-delay circuit comprises an RC circuit; and wherein said RC circuit includes an integrated circuit capacitor and a high impedance of series antifuse coupled in parallel to said integrated circuit capacitor as a discharging resistor.
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9. A method of cloaking an RFID tag in an RF field comprising:
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powering said RFID tag in said RF field; generating a logic signal, CLOAK, on a predetermined condition as determined by said RFID tag; activating a time-delay circuit upon generation of said logic signal, CLOAK, to generate a predetermined time delay; activating a switch to effectively open circuit said antenna for said predetermined time delay so that the effective absorption and scattering aperture of said antenna are minimized during said predetermined time delay. - View Dependent Claims (10, 11)
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12. A plurality of RFID tags, each RFID tag having a cloaking circuit coupled to an RFID tag comprising:
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an antenna; a switch in series with said antenna to selectively disconnect said antenna from said RFID tag, said switch being coupled between said antenna and said RFID tag; a time delay circuit coupled to said switch for disconnecting said antenna for a predetermined time period; and a logic circuit coupled to said time delay circuit for selectively activating said time delay circuit so that said antenna is provided with a substantially reduced effective absorbing and scattering aperture during said predetermined time period relative to other ones of said plurality of RFID tags in a common interrogation RF field. - View Dependent Claims (13, 15, 16)
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14. A plurality of RFID tags, each RFID tag having a cloaking circuit coupled to an RFID tag comprising:
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an antenna; a switch in series with said antenna to selectively disconnect said antenna from said RFID tag, said switch being coupled between said antenna and said RFID tag; a time delay circuit coupled to said switch for disconnecting said switch for a predetermined time period; and a logic circuit coupled to said time delay circuit for selectively activating said time delay circuit so that said antenna is provided with a substantially reduced effective absorbing and scattering aperture during said predetermined time period relative to other ones of said plurality of RFID tags in a common interrogation RF field; and wherein time delay circuit is comprised of a capacitor and a parallel high impedance resistor, said resistor comprising a plurality of series coupled integrated circuit antifuses.
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17. A method of cloaking an RFID tag in an RF field comprising:
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generating a logic signal, CLOAK, on a predetermined condition as determined by said RFID tag; and selectively coupling a high impedance load across an antenna coupled to said RFID tag to cause said antenna for said predetermined time period to exhibit an absorption and scattering aperture similar to an open circuited antenna. - View Dependent Claims (18)
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Specification