Reader for use in a radio frequency identification system and method thereof

• US 6,362,738 B1
• Filed: 09/08/1999
• Issued: 03/26/2002
• Est. Priority Date: 04/16/1998
• Status: Expired due to Term

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Vega, Victor
• Primary Examiner(s): Wu, Daniel J.
• Assistant Examiner(s): PHAM, TOAN NGOC
• Application Number:
  US09/391,725
• Time in Patent Office: 930 Days
• Field of Search: 340/572.1, 340/572.7, 340/568.1, 340/539, 340/10.1, 340/10.4, 340/10.51, 340/10.52, 340/10.3, 340/10.41, 340/825.06, 340/572.8, 342/429, 342/445, 343/751, 343/777, 343/853, 343/894, 235/435-453
• US Class Current: 340/572.1
• CPC Class Codes: G06K 19/0701 at least one of the integrated circuit chips comprising an arrangement for power management
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 19/07788 the antenna being of the capacitive type
• 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 7/10069 the collision being resolved in the frequency domain, e.g. by hopping from one frequency to the other frequency hopping or spread spectrum techniques H04B7/00
• CPC Class Codes: G06K 7/10326 the antenna being of the very-near field type, e.g. capacitive
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip

Abstract

A contactless programmable electrostatic Radio Frequency Identification (RFID) reader that also serves as an Electronic Article Surveillance (EAS) reader is described. The RFID/EAS reader contains a detector circuit for detecting the presence of a signal carrier frequency transmitted by the transponder in response to a signal from the reader. The detector circuit has a resonator circuit which is connected to a receiver electrode. The resonator comprises a piezoelectric element with a high quality factor ‘Q’ at the resonant frequency to enhance sensitivity. The alarm carrier signal is rectified and fed to either a peak detector or an envelope detector circuit. A voltage source generates a voltage threshold to allow for operating range adjustment. A comparator compares both voltages and generates an alarm signal if the voltage signal reaches the threshold voltage. The RFID/EAS further having the capability to read the RFID contents. Alternatively, an electrostatic EAS reader (without RFID capability) having a substantially similar detector circuit is also described.

Claims

1. A reader comprising:

a processor coupled to a host computer;

at least a first electrode;

an exciter, coupled to the processor and at least the first electrode, for generating and transmitting an electrostatic excitation signal having a first carrier frequency;

at least a second electrode;

a receiver, coupled to at least the second electrode, for receiving an RF signal via electrostatic means; and

a detector circuit, coupled to at least the second electrode, for detecting an alarm signal having a second carrier frequency, the detector circuit amplifying the alarm signal if the second carrier frequency is sensed.

2. The reader of claim 1 wherein the exciter is a piezoelectric element.

3. A reader comprising:

a processor coupled to a host computer storing a database;

at least a first electrode;

an exciter coupled to the processor and at least the first electrode, the exciter generating and transmitting an exciter signal having a first carrier frequency over at least the first electrode;

at least a second electrode;

a receiver coupled to at least the second electrode, the receiver receiving a RF signal, the receiver demodulating the RF signal and passing it to the processor; and

a detector circuit coupled to at least the second electrode for detecting an alarm signal having a second carrier frequency, the detector circuit amplifying the alarm signal if the second carrier frequency is sensed, wherein the detector circuit comprises;

a resonator circuit comprising a piezoelectric element having a high Q factor, the piezoelectric element coupled to the at least one second electrode, the piezoelectric element passively amplifying the alarm signal detected across at least the second electrode at resonant frequency;

an envelope detector coupled to the piezoelectric element, the envelope detector generating an envelope detector signal in response to the alarm signal; and

a comparator receiving as inputs the envelope detector signal and a threshold signal, the comparator generating a signal when the envelope detector signal reaches the threshold signal.

4. The reader of claim 3, wherein the detector circuit further comprises a voltage source coupled to the comparator for generating the threshold signal.

5. The reader of claim 4, wherein the voltage source comprises a digital-to-analog converter (DAC) coupled to the comparator, the DAC generating the threshold signal under control of the processor.

6. The reader claim 4, wherein the detector circuit further comprises a zener diode coupled in parallel to a second capacitor for governing the envelope detector signal to a desirable level.

7. The reader claim 6, wherein the detector circuit further comprises an operational amplifier coupled to a plurality of diodes and the piezoelectric element.

8. The reader of claim 3, wherein the piezoelectric element comprises a piezoelectric ceramic resonator.

9. The reader of claim 3, wherein the piezoelectric element comprises a piezoelectric quartz crystal.

10. The reader of claim 3, wherein the piezoelectric element comprises a piezoelectric lithium niobate crystal.

11. The reader of claim 3, wherein the detector circuit comprises a phase-locked loop circuit.

12. A system comprising a reader and a plurality of transponders,

the reader comprising:

a processor coupled to a host computer;

at least one first electrode;

an exciter coupled to the processor and the at least one first electrode, the exciter generating and transmitting an exciter signal having a first carrier frequency over the at least one first electrode;

at least one second electrode;

a receiver coupled to the at least one second electrode, the receiver receiving a RF signal, the receiver demodulating the RF signal and passing it to the processor; and

a detector circuit coupled to the at least one second electrode for detecting an alarm signal having a second carrier frequency, the detector circuit amplifying the alarm signal if the second carrier frequency is sensed;

each one of the plurality of transponders comprising;

a third plurality of electrodes for receiving the exciter signal and transmitting the alarm signal;

an analog interface module coupled to the third plurality of electrodes, the analog interface module extracting a power signal and a clock signal having a first carrier frequency from an RF exciter signal received by the third plurality of electrodes, the analog interface module rectifying and regulating the exciter signal for use in activating the electrostatic transponder;

a memory for storing data;

a modulator coupled to the memory, the modulator modulating data information stored in the memory with a second carrier frequency; and

a controller coupled to the analog interface module and the memory, if a RFID mode is involved, the controller reading data information from the memory and sending the data information to the analog interface module for transmitting over the third plurality of electrodes, if a EAS mode is involved, the controller sending the alarm signal to the analog interface module for sending over the third plurality of electrodes.

13. A reader comprising:

at least a first electrode;

an exciter, coupled to at least the first electrode, for generating and transmitting an electrostatic exciter signal having a first carrier frequency;

at least a second electrode; and

a detector circuit, coupled to at least the second electrode, for detecting an alarm signal having a second carrier frequency,

wherein at least one of the exciter and the detector circuit comprises a piezoelectric element.

14. The reader of claim 13, wherein the detector circuit comprises a phase-locked loop circuit.

15. The reader of claim 13 wherein the detector circuit comprises a piezoelectric element.

16. A reader comprising:

at least a first electrode;

an exciter coupled to at least the first electrode, the exciter generating and transmitting an exciter signal having a first carrier frequency over at least the first electrode;

at least a second electrode; and

a detector circuit coupled to at least the second electrode, the detector circuit detecting an alarm signal having a second carrier frequency, the detector circuit amplifying the alarm signal if the second carrier frequency is sensed, wherein the detector circuit comprises;

a resonator circuit comprising a piezoelectric element having a high Q factor, the piezoelectric element coupled to at least the second electrode;

the piezoelectric element passively amplifying the alarm signal detected across at least the second electrode at resonant frequency;

an envelope detector coupled to the piezoelectric element, the envelope detector generating an envelope detector signal; and

a comparator receiving as inputs the envelope detector signal and a threshold signal, the comparator generating a signal when the envelope detector signal reaches the threshold signal.

17. The reader of claim 16, wherein the detector circuit further comprises a voltage source coupled to the comparator for generating the threshold signal.

18. The reader of claim 17, wherein the voltage source comprises a variable voltage source.

19. The reader claim 17, wherein the detector circuit further comprises a zener diode coupled in parallel to a second capacitor for governing the envelope detector signal to a desirable level.

20. The reader of claim 19, wherein the detector circuit further comprises an operational amplifier coupled to a plurality of diodes and the piezoelectric element.

21. A method comprising the steps of:

a) receiving a radio frequency signal via electrostatic means;

b) detecting a carrier frequency for the radio frequency signal using a piezoelectric element;

c) rectifying the radio frequency signal, when the carrier frequency is sensed, to generate a rectified signal;

d) generating a detector signal by tracking the rectified signal;

e) generating a threshold signal;

f) comparing the detector signal to the threshold signal; and

g) generating an alarm signal when the detector signal reaches the threshold signal.

22. The method of claim 21, further comprising the step of passively amplifying the alarm signal at resonant frequency using an piezoelectric element.

23. The method of claim 21, wherein the step of detecting a carrier frequency is performing via a phase-locked loop circuit.