Passive transponder

• US 5,680,459 A
• Filed: 04/28/1995
• Issued: 10/21/1997
• Est. Priority Date: 04/29/1994
• Status: Expired due to Term

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Kasten Chase Applied Research Limited
• Inventors: Hall, Chris, Hook, Christopher, Paun, Dimitrie Octavian, Juson, Keith, Oprea, Alexandru, Ferguson, Donald Harold
• Primary Examiner(s): Cain, David C.
• Application Number:
  US08/430,825
• Time in Patent Office: 907 Days
• Field of Search: 380/23, 380/49
• US Class Current: 705/65
• CPC Class Codes: G01S 13/758 using a signal generator powered by the interrogation signal
• 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: G06Q 20/367 involving electronic purses or money safes
• CPC Class Codes: G07B 15/063 using wireless information transmission between the vehicle and a fixed station identification of vehicles G08G

Abstract

The present invention relates to an electronic identification system comprising one or more transponders which store identification and other information in memory, and readers, which capture information from the transponders and write new information thereto, and in which communications between transponders and readers are accomplished using radio frequency signals. The present invention has attributes which make it particularly useful in automatic fare collection systems, where transponders, typically in the form of thin cards and used as pre-paid tickets, are carried by fare paying passengers to replace printed tickets and eliminate exchange of cash. Specifically the system achieves simultaneous identification of numerous transponders by one reader, permits a reader to selectively program any of many transponders under its control, exhibits fast transaction speed to maximize passenger throughput, and achieves exceptional data storage integrity.

Claims

1. In a radio frequency transponder system including an input for receiving a radio frequency signal modulated with data, said data including an error check field, a circuit for demodulating said signal so as to recover said data in serial format, and data memory for storing said data, the improvement comprising a first circuit for receiving said data in serial format and converting said data to parallel format, a second circuit for assessing any errors in said data with reference to said error check field and in the event said data is free of errors then storing said data in parallel format in said memory as a succession of pages each comprising one or more bytes of said data.

2. The improvement of claim 1, wherein said first circuit comprises a scratchpad memory for bit-serially receiving and accumulating said data to form a page of said data for parallel storage in said data memory.

3. The improvement of claim 1, wherein said second circuit comprises control and error check logic for performing a cyclic redundancy check on said error check field for assessing any said errors in said data, and an address decoder and latch for storing said data in said data memory.

4. A method of transferring data from a reader to at least one transponder in a communication system, comprising the steps of:

a) transmitting a packet of said data from said reader to said transponder, wherein said data includes an error check field;

b) assessing within said transponder whether said data contains any errors with reference to said error check field;

c) in the event said data is free of errors then storing said data in said transponder and transmitting an acknowledgement message from said transponder to said reader for reporting completion of said storing of said data; and

d) in the event said data contains an error then transmitting a predetermined message from said transponder to said reader for indicating that said data has been corrupted, thereby initiating re-transmission of said packet of data from said reader to said transponder.

5. In a radio frequency transponder for receiving data from a reader, said data including an address for identifying said transponder from among a plurality of transponders, the improvement comprising a fixed code area in said transponder for storing a unique identification number for said transponder, and logic circuitry for comparing said address included in said data received from said reader with said identification number so as to thereby ascertain whether said data is intended for said transponder from among said of transponders.

6. The improvement of claim 5, wherein said unique identification number is stored in said fixed code area of said transponder via laser fusing.

7. The improvement of claim 6, wherein said address is encrypted and wherein said transponder further includes security logic circuitry for decrypting said address and encrypting said identification number.

8. In a passive transponder system for receiving a radio frequency signal modulated with programming instruction data from a reader, deriving operating power from said radio frequency signal, demodulating said programming instruction data from said radio frequency signal and in response effecting internal re-programming, the improvement comprising:

a) an energy level detector for detecting energy available in said radio frequency signal; and

b) control connected to said energy level detector for determining whether sufficient energy is available in said radio frequency signal to effect said re-programming in accordance with said programming instruction data, and in the event sufficient energy is available then effecting said re-programming, and in the event that insufficient energy is available then transmitting a message to said reader for notifying the reader that re-programming cannot be effected.

9. In a passive transponder system having an antenna for receiving a radio frequency signal modulated with data a reader, circuitry for deriving operating power from said radio frequency signal, and further circuitry for demodulating said data from said radio frequency signal, the improvement comprising:

a) an energy level detector for detecting energy available in said radio frequency signal; and

b) an automatic gain circuit connected to said energy level detector and said antenna for varying load resistance to said antenna by increasing said resistance when said energy available is less than a predetermined amount, and decreasing said resistance when said energy available is greater than said predetermined amount, thereby dynamically varying loaded quality factor (Q) of said transponder relative to distance between said reader and said transponder so as to provide a wide dynamic operating range of said transponder.

10. A communication system comprising:

a) a reader for generating a radio frequency excitation field;

b) a plurality of radio frequency transponders, each of said transponders being capable of transmitting a message to said reader immediately upon detecting said excitation field; and

c) circuitry within each of said transponders for detecting transmission of messages to said reader by other ones of said transponders and in response delaying transmission of said message to said reader by a predetermined time period, thereby avoiding interference between said plurality of transponders.