Accurate persistent nodes
First Claim
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1. A method for counting Radio Frequency Identification (RFID) tags, comprising:
- sending no select commands to RFID tags in range of a reader for at least a known period of time for ensuring that all of the RFID tags in range of the reader are in an active state;
interrogating each of the RFID tags in range of the reader;
receiving a tag identifier from each RFID tag;
instructing each tag to sleep upon receiving the tag identifier from the tag,wherein each tag remains in the sleep state for the known period of time,wherein the known period of time does not significantly vary regardless of whether the tag is powered or not, andgenerating a count of the tags,wherein the RFID tags each comprise a calibrated gate biasing circuit having a switched capacitor precision resistor and a voltage reference,wherein the voltage reference includes a matrix of forward biased diodes coupled to an outlet of the switched capacitor precision resistor.
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Abstract
A timing circuit that can function as an accurate persistent node in an RFID tag includes a power capture circuit for capturing power from a power source, and a counter circuit that provides a count representing a progression of time. The count can then be compared to a reference value representing a time constant of the circuit.
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Citations
14 Claims
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1. A method for counting Radio Frequency Identification (RFID) tags, comprising:
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sending no select commands to RFID tags in range of a reader for at least a known period of time for ensuring that all of the RFID tags in range of the reader are in an active state; interrogating each of the RFID tags in range of the reader; receiving a tag identifier from each RFID tag; instructing each tag to sleep upon receiving the tag identifier from the tag, wherein each tag remains in the sleep state for the known period of time, wherein the known period of time does not significantly vary regardless of whether the tag is powered or not, and generating a count of the tags, wherein the RFID tags each comprise a calibrated gate biasing circuit having a switched capacitor precision resistor and a voltage reference, wherein the voltage reference includes a matrix of forward biased diodes coupled to an outlet of the switched capacitor precision resistor. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for counting Radio Frequency Identification (RFID) tags, comprising:
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interrogating each RFID tag in range of a reader; receiving a tag identifier from each RFID tag; instructing each tag to sleep upon receiving the tag identifier from the tag, wherein each tag automatically returns to a wake state after a time interval has elapsed, wherein the time interval is bounded between a minimum and a maximum value, wherein the minimum and maximum values are in a range of 200 to 2000 ms; and generating a count of the tags, wherein each RFID tag comprises a calibrated gate biasing circuit having a switched capacitor precision resistor and a voltage reference, wherein the voltage reference includes a matrix of forward biased diodes coupled to an outlet of the switched capacitor precision resistor. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification