Subset selection of RFID tags using light
Methods and apparatuses for selecting a subset of RFID tags are provided in some embodiments. These methods and apparatuses utilize the susceptibility to light by persistent nodes found in passive tags. Light can be used to intentionally reduce persistence times in a particular subset tags or even an individual tag. Then, persistent nodes can be used as a selection criterion to distinguish previously illuminated tags from non-illuminated tags. In other embodiments, a power circuit receives a RF input source and generates a direct current (DC) output voltage. The circuit includes a bias circuit to supply a gate to source bias, which is independent of the DC output voltage. The circuit further includes a voltage multiplier circuit that is coupled to the bias circuit. The voltage multiplier circuit has MOS transistors with one transistor to receive the gate to source bias.
1. A radio frequency identification (RFID) system comprising:
a tag with an integrated circuit having at least one flag, the at least one flag having a persistence time reduced by exposure to light;
an RFID reader; and
a light source configured to reduce the persistence time.
2. The RFID system of claim 1 wherein the light source is a localized light source.
3. The RFID system of claim 1 wherein the flag is a logic value indicating a tag selection state.
4. The RFID system of claim 1 wherein the light source produces infrared electromagnetic waves.
5. The RFID system of claim 1 wherein the light source is an infrared light emitting diode.
6. The RFID system of claim 1 wherein the RFID reader is a handheld reader.
7. The RFID system of claim 1 wherein the RFID reader is configured to receive backscatter modulated data from the tag within a band of 860 MHz to 960 MHz.
8. The RFID system of claim 1 wherein the RFID reader is configured to receive data from the tag within a band of 13.56 MHz±10%.
9. The RFID system of claim 1 wherein the integrated circuit includes a second flag having a persistence time unaffected by the exposure to light.
10. The RFID system of claim 9 wherein a second flag's persistence time is reduced by a frequency differing from the exposure.
11. A radio frequency identification (RFID) reader comprising:
a radio frequency source;
an antenna to transmit radio frequency waves generated by the radio frequency source; and
a light source to transmit light waves that manipulate a persistence time of an RFID tag,
wherein the antenna transmits radio frequency waves to a first area and the light source transmits to a second area, the second area being a proper subset of the first area.
12. The RFID reader of claim wherein the light source is an infrared source and the light waves include infrared electromagnetic waves.
13. A method for selecting a subset of radio frequency identification (RFID) tags comprising:
setting a persistent node for each of the plurality of passive tags to a first logic value, the node capable of maintaining the first logic value for a first time period in the absence of power;
interrupting power to the passive tag for a second time period, the second time period being shorter than the first time period; and
illuminating a subset of the plurality of tags with light during at least a portion of the second time period, persistent nodes of the subset degenerating to a second logic value during the second time period.
14. The method of claim 13 further comprising:
querying, after the second time period, passive tags having nodes with a first logic value, but not passive tags having nodes with a second logic value.
15. The method of claim 13 further comprising:
querying, after the second time period, passive tags having nodes with a second logic value, but not passive tags having nodes with a first logic value.
16. The method of claim 13 wherein the subset includes a single passive tag.
17. The method of claim 13 wherein a web includes the plurality of passive tags.
18. The method of claim 13 wherein a web includes the plurality of strap assemblies.
19. The method of claim 13 further comprising testing the subset for operational performance.
20. The method of claim 19 further comprising advancing a web and illuminating another subset.
21. The method of claim 13 wherein each of the plurality of passive tags includes at least one persistent node unaffected by illumination to light.
22. A method for selecting a subset of radio frequency identification (RFID) tags comprising:
broadcasting an interrogating signal to set a persistent node for each of the plurality of passive tags to a first logic value, the node capable of maintaining the first logic value for a first time period in the absence of power;
interrupting power to the passive tag for a second time period by ceasing the broadcasting, the second time period being shorter than the first time period; and
illuminating a subset of the plurality of tags with an illuminating source during at least a portion of the second time period, persistent nodes of the subset degenerating to a second logic value during the second time period,
wherein the interrogating signal is a broad beam relative to the narrow beam of the illuminating source.