Method and apparatus for radiofrequency identification tags

• US 5,856,788 A
• Filed: 03/12/1996
• Issued: 01/05/1999
• Est. Priority Date: 03/12/1996
• Status: Expired due to Term

• Current Assignee: Neology Incorporated (OEP Technologie BV)
• Original Assignee: Single Chip Systems Corporation (OEP Technologie BV)
• Inventors: Walter, Ronald, Vertrees, Keith
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): Beaulieu, Yonel
• Application Number:
  US08/628,872
• Time in Patent Office: 1,029 Days
• Field of Search: 340/825.54, 340/825.49, 340/505, 340/568, 340/572, 340/825.34, 340/825.35, 340/825.02, 340/825.08, 235/375, 235/380, 342/44, 342/51
• US Class Current: 340/10.2
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10039 interrogator driven, i.e. synchronous
• CPC Class Codes: G07C 9/28 the pass enabling tracking or indicating presence

Abstract

A method and apparatus for determining the identification number or any other information within a plurality of radiofrequency identification tags within a common field of interrogation utilizes a combination of an isolation state into which the tags may be placed together with bitwise interrogation of the identification number or information followed by selective deactivation. A first bit in the identification number or information is interrogated of all the tags in the field. If any tag responds that the bit is a 1, a 1 is entered into an ID register in a reader and all tags in which a 0 exists in that bit position are deactivated. The process continues until only one tag remains activated. The last activated tag at this point has been completely read and is then placed in an isolated state. The process is begun anew with the remaining nonisolated tags until all tags have been read.

Claims

1. An improvement in a method for identifying each one of a plurality of radiofrequency-identification tags simultaneously interrogated on a single communication channel within a field of interrogation comprising the steps of:

activating said plurality of tags, each of said tags identified by a plurality of sequential bits; and

interrogating a selected bit of said plurality of sequential bits of each of said plurality of tags to obtain a predetermined response from each of said tags having a predetermined bit value for said selected bit and upon receiving said predetermined response indicating at least one tag having said predetermined bit value then selectively deactivating each other one of said plurality of tags having a different bit value than said predetermined bit value for said selected bit, so that response from each of said deactivated tags to any interrogation is prohibited until one tag of said plurality of tags has been completely identified, otherwise if no tag which is present within said interrogation field responds to said interrogation to indicate said predetermined bit value, then no tag present within said field of interrogation is deactivated;

repeating said step of interrogating each of said sequential bits in said plurality of tags and said step of selectively deactivating said each other one of said plurality of tags until all of said sequential bits are obtained for at least one of said tags,

so that said information is unambiguously obtained from said plurality of tags in said field of interrogation.

2. The improvement of claim 1 where said repeated steps of interrogating said activated tags comprises serially interrogating said activated tags to obtain in serial sequence a complete sequence of said sequential bits for a tag.

3. The improvement of claim 1 where said repeated steps of interrogating said activated tags comprises the steps of interrogating said activated tags to obtain in an arbitrary, nonserial sequence a complete sequence of said sequential bits for a tag.

4. The improvement of claim 1 further comprising the step of determining when said sequential bits have been completely interrogated from one of said plurality of tags and verifying said sequential bits, said method being restarted anew if verification fails.

5. The improvement of claim 1 where interrogating said activated tags while deactivating each other one of said tags having a different bit value than said predetermined bit value comprises simultaneously generating a response signal from those of said plurality of tags having said predetermined bit value, and deactivating all of said others of said plurality of tags not having said predetermined bit value.

6. The improvement of claim 1 where interrogating said activated tags while deactivating each of said tags having a different bit value than said predetermined bit value comprises first generating a response signal from those of said plurality of tags having said predetermined bit value, and subsequently deactivating others of said plurality of tags not having said predetermined bit value.

7. The improvement of claim 1 further comprising isolating each of said tags when said sequential bits are completely read from said tag to prevent said isolated tag'"'"'s continued response to interrogation when unread ones of said plurality of tags are subsequently interrogated.

8. The improvement of claim 7 further comprising determining when said sequential bits have been completely interrogated from one of said plurality of tags and verifying said sequential bits, said method being restarted anew if verification fails.

9. The apparatus of claim 1 where said means for interrogating said activated tags generates a response signal from those of said plurality of tags having said predetermined bit value prior to deactivation of said plurality of tags not having said predetermined bit value.

10. The improvement of claim 1 where said step of deactivating comprises deactivating said other one of said plurality of tags having a different bit value than said predetermined bit value with a command signal of reduced bit length.

11. The improvement of claim 10 where said step of deactivating said other one of said plurality of tags having a different bit value than said predetermined bit value with a command signal of reduced bit length comprises deactivating said other one of said plurality of tags with a command of one bit length.

12. An apparatus for obtaining digital information from a plurality of radiofrequency-identification tags simultaneously interrogated on a single communication channel within a field of interrogation comprising:

means for activating said plurality of tags; and

means for bitwise interrogating each of said plurality of tags for a bit value of a sequentially selected bit of said digital information in each tag, to obtain a bitwise predetermined response while;

means for deactivating, with each interrogation, each of said tags present within said field of interrogation having a different bit value than a predetermined bit value for said sequentially selected bit, said deactivated tag being prohibited from responding to further interrogation, otherwise if no tag present within said field of interrogation responds to said interrogation to indicate said predetermined bit value, no tag present within said field of interrogation is deactivated, said sequentially selected bit being indexed until all of said digital information is identified in one of said plurality of tags present within said field of interrogation, all of said other ones of said plurality of tags present within said field of interrogation being deactivated, said deactivated tags present within said field of interrogation not further responding to any interrogation until all of said digital information is identified in said one of said plurality of tags present within said field of interrogation,

so that said information is unambiguously obtained from said plurality of tags in said field of interrogation.

13. The apparatus of claim 12 where said means for bitwise interrogating said activated tags comprises means for serially bitwise interrogating said activated tags in an ordered sequence.

14. The apparatus of claim 12 where said means for bitwise interrogating said activated tags comprises means for arbitrarily bitwise interrogating said activated tags in an order other than an ordered sequence without repeating an interrogation of any given bit of said digital information.

15. The apparatus of claim 12 further comprising means for determining when said digital information has been completely interrogated from one of said plurality of tags and for verifying said digital information, said means for interrogating said activated tags being restarted anew if verification fails.

16. The apparatus of claim 12 where said means for interrogating said activated tags simultaneously generates a response signal in those of said plurality of tags having said predetermined bit value with deactivation of said plurality of tags not having said predetermined bit value.

17. The apparatus of claim 12 further comprising means for isolating each of said tags when said digital information is completely read from said tag to prevent its continued response to interrogation from said read tag when unread ones of said plurality of tags are subsequently interrogated.

18. A system for communicating with a plurality of tags within a field of interrogation on a single communication frequency wherein said plurality of tags communicate in response to interrogation during said same time period, wherein each of said plurality of tags can be set in an activated AWAKE state or deactivated into a SLEEP state in which response by said tag in said SLEEP state is prohibited until a tag in said field has been completely identified, wherein each of said tags contains digital information, and wherein each of said tags can be set in two distinguishable states, an ISOLATED state and NOT ISOLATED state in which response by said tag in said ISOLATED state is prohibited until all tags in said field have been completely identified, said system comprising:

first means for setting all of said tags which are in said NOT ISOLATED state into said activated AWAKE state;

second means for interrogating each bit in said digital information stored within each of said tags in said activated AWAKE state to determine if said interrogated bit has a predetermined logic value, and if so to cause each tag to generate a predetermined response if said bit has said predetermined value and otherwise to place said tag in said SLEEP state;

third means for bitwise accumulating said predetermined responses and lack of said predetermined responses by bit-by-bit reading said digital information from one of said plurality of tags; and

fourth means for placing each said tag from which said digital information has been bitwise completely read into said ISOLATED state so that subsequent operation of said second and third means reads each unique codification of said digital information contained within each of said plurality of tags within said field of interrogation.

19. The system of claim 18 where said second means generates two separate sequential commands to generate said predetermined response from selected ones of said tags and to deactivate other ones of said tags.

20. The system of claim 18 where said second means generates a single command to simultaneously generate said predetermined response from selected ones of said tags and to deactivate other ones of said tags.

21. A method for interrogating a plurality of RF/ID tags in a single field of interrogation wherein said RF/ID tags communicate on a single frequency during at least overlapping time periods comprising the steps of:

bitwise interrogating each of said plurality of tags to determine if any one of said plurality of tags has a predetermined logic value in a predetermined one of a sequence of bit positions;

deactivating each of said tags not having said predetermined logic value in said predetermined one of said sequential bit positions, so that said deactivated tags are prohibited from responding to any interrogation until a tag has been completely identified;

repeating said steps of interrogating and deactivating said plurality tags until only one tag remains activated;

obtaining information from said only one activated tag;

isolating said one activated tag after said information is obtained therefrom, so that said isolated tag is prohibited from responding to any interrogation until all tags within said field have been completely identified; and

repeating each of said foregoing steps for all tags not isolated until complete information has been read from each of said plurality of tags within said field of interrogation.

22. A method for interrogating a plurality of RF/ID tags in a single field of interrogation wherein said RF/ID tags communicate on a single frequency during at least overlapping time periods with a single reader comprising the steps of:

transmitting a train of synchronization pulses from said reader to said tags, each said synchronization pulse in said train of synchronization pulses having a predetermined pulse width, t₁, said train of synchronization pulses being repeated in a subsequent train of synchronization pulses after a predetermined period, t₂ ;

transmitting reader digital data from said reader to said plurality of tags by transmitting a selected number of synchronization pulses in said train of synchronization pulses, each with a predetermined pulse separation of t₃,; and

transmitting digital data from said plurality of tags to said reader by selectively transmitting a tag data pulse in a selected half of a tag data frame defined by two consecutive synchronization pulses transmitted by said reader.

23. The method of claim 22 wherein transmitting a train of synchronization pulses is defined by ceasing the transmission of a signal from said reader to said tags for said predetermined pulse width, t₁, and repeating said cessation after said predetermined period, t₂.

24. The method of claim 22 wherein transmitting tag digital data from said plurality of tags to said reader comprises transmitting said tag digital data after the last of said reader digital data is transmitted from said reader to said tags, said last reader digital data establishing the beginning of said tag data frame, two of said synchronization pulses defining a first and second half of said tag data frame, said tag data being transmitted to said reader from said tag by a pulse of width t₁ during either said first or second half of said tag data frame to indicate a logical binary value.