Method of interrogating a plurality of transponders arranged in the transmission range of an interrogating device and transponders for use in the said method

• US 5,294,931 A
• Filed: 04/29/1992
• Issued: 03/15/1994
• Est. Priority Date: 04/29/1992
• Status: Expired due to Fees

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments Deutschland Gesellschaft Mit Beschrã¤Nkter Haftung (Texas Instruments, Inc.)
• Inventors: Meier, Herbert
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US07/875,518
• Time in Patent Office: 685 Days
• Field of Search: 342/44, 342/51
• US Class Current: 342/44
• 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

Abstract

A single interrogation device interrogates a plurality of transponders arranged within the range of transmission of the interrogation device and identifies them without any mutual interference.

The interference free operation is obtained by the interrogation device sequentially transmitting a plurality of RF interrogation pulses, separated from each other in time and whose energy changes from one pulse to the next one, to transponders which have an energy storage element and which respond to the interrogation pulses with an answer signal in dependence upon the condition that, at the end of each interrogation pulse, the charge voltage present at the energy storage element falls within a predetermined voltage range.

Claims

1. A method for interrogating and identifying a plurality of batteryless transponders arranged in the transmission range of an interrogation device wherein only those transponders which have stored an amount of voltage which falls within their predetermined window respond, comprising the steps of:

transmitting interrogation pulses with intervals of time between them, whose energy changes from pulse to pulse;

receiving said interrogation pulses;

rectifying said received interrogation pulses;

storing said rectified interrogation pulses as a charge voltage at an energy storage element;

detecting the termination of said interrogation pulses;

comparing the amount of charge voltage stored at said energy storage element to a predetermined voltage range, said predetermined voltage range having an upper voltage limit and a lower voltage limit, beyond which said transponder could respond but-for said comparing the amount of charge voltage to said predetermined voltage range;

transmitting an answer signal in response to the termination of said interrogation pulses and in response to said charge voltage falling within said predetermined voltage range.

2. The method as claimed in claim 1, wherein the RF interrogation pulses transmitted with intervals of time between them have the same duration and increase in amplitude from one pulse to the next one.

3. The method as claimed in claim 1, wherein the Rf interrogation pulses transmitted with intervals of time between them have the same amplitude and increase in duration from one pulse to the next one.

4. A transponder for use in a remote identification system wherein there are more than one transponders within the interrogation range of an interrogator wherein the purpose is to have one transponder respond at a time to prevent interference between them comprising:

an antenna for reception of an interrogation signal and transmission of a transponder answer signal;

a rectifier for rectification of said received interrogation signal;

an energy storage element operable to be charged with said rectified interrogation signal in the form of a charge voltage;

a window comparator, to whose input said charge voltage of said energy storage element is applied and at whose output an enable signal is produced in response to said charge voltage falling within a predetermined range, said predetermined range having an upper voltage limit and a lower voltage limit beyond which said transponder could respond but-for said enable signal being produced in response to said charge voltage falling within a predetermined range, the enable signal transmission of the transponder answer signal.