Passive RFID tag that retains state after temporary loss of power
DC CAFCFirst Claim
1. An RFID transponder, comprising:
- an RF front end adapted to receive an interrogating RF signal;
an analog circuit coupled to said RF front end and adapted to recover analog signals from said received interrogating RF signal, said analog circuit providing state information defining a desired state of said RFID transponder corresponding to said analog signals;
a digital state machine coupled to said analog circuit and adapted to execute at least one command in accordance with said state information;
a memory coupled to said digital state machine and adapted to store and retrieve digital data responsive to said at least one command executed by said digital state machine a power capacitor coupled to said analog circuit and deriving a voltage rectified from said interrogating RF signal to charge said power capacitor, said power capacitor thereby providing electrical power for said analog circuit, said digital state machine and said memory; and
a state holding cell coupled to said digital state machine and being adapted to maintain said state information during a loss in power provided by said power capacitor due to lapse in receipt of said interrogating RF signal by said RF front end.
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Abstract
The present invention provides an RFID transponder that includes a state holding cell that maintains the present state of the RFID transponder during temporary losses of power. After power is restored to the RFID transponder, the state holding cell restores the present state to the RFID transponder so that transactions with an RFID interrogator can continue without having re-transmit redundant commands. The RFID transponder further comprises an RF front end adapted to receive an interrogating RF signal. An analog circuit is coupled to the RF front end and is adapted to recover analog signals from the received interrogating RF signal. The analog circuit provides state information defining a desired state of the RFID transponder corresponding to the analog signals. A digital state machine is coupled to the analog circuit and adapted to execute at least one command in accordance with the state information. A memory is coupled to the digital state machine and is adapted to store and retrieve digital data responsive to the at least one command executed by the digital state machine. A power capacitor is coupled to the RF front end and derives a voltage rectified from the interrogating RF signal to charge the power capacitor. The power capacitor thereby provides electrical power for the analog circuit, the digital state machine and the memory. The state holding cell is coupled to the analog circuit and the digital state machine and is adapted to maintain the state information during a loss in power provided by the power capacitor due to lapse in receipt of the interrogating RF signal by the RF front end.
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Citations
24 Claims
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1. An RFID transponder, comprising:
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an RF front end adapted to receive an interrogating RF signal;
an analog circuit coupled to said RF front end and adapted to recover analog signals from said received interrogating RF signal, said analog circuit providing state information defining a desired state of said RFID transponder corresponding to said analog signals;
a digital state machine coupled to said analog circuit and adapted to execute at least one command in accordance with said state information;
a memory coupled to said digital state machine and adapted to store and retrieve digital data responsive to said at least one command executed by said digital state machine a power capacitor coupled to said analog circuit and deriving a voltage rectified from said interrogating RF signal to charge said power capacitor, said power capacitor thereby providing electrical power for said analog circuit, said digital state machine and said memory; and
a state holding cell coupled to said digital state machine and being adapted to maintain said state information during a loss in power provided by said power capacitor due to lapse in receipt of said interrogating RF signal by said RF front end. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An RFID transponder, comprising:
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means for receiving an interrogating RF signal;
means for recovering analog signals from said received interrogating RF signal and providing state information defining a desired state of said RFID transponder corresponding to said analog signals;
means for executing at least one command in accordance with said state information;
means for storing and retrieving digital data responsive to said at least one command;
means for providing electrical power for said RFID transponder derived from said interrogating RF signal; and
means for maintaining said state information during a temporary lapse in receipt of said interrogating RF signal. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method for operating an RFID transponder, comprising the steps of:
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receiving an interrogating RF signal;
recovering analog signals from said received interrogating RF signal and providing state information defining a desired state of said RFID transponder corresponding to said analog signals;
executing at least one command in accordance with said state information;
storing and retrieving digital data responsive to said at least one command;
providing electrical power for said RFID transponder derived from said interrogating RF signal; and
maintaining said state information during a temporary lapse in receipt of said interrogating RF signal. - View Dependent Claims (22, 23, 24)
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Specification