Self Tuning RFID

• US 20100019907A1
• Filed: 07/28/2008
• Published: 01/28/2010
• Est. Priority Date: 07/28/2008
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Shanks, Wayne E.
• Granted Patent: US 8,836,512 B2
• Time in Patent Office: Days
• US Class Current: 340/572.500
• CPC Class Codes: G06K 19/0713 the arrangement including a power charge pump
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• 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

Abstract

The antenna of an RFID tag is automatically tuned by controlling both the real and imaginary components impedance “seen” by the antenna. The real component (resistive) is controlled by controlling a tap of a charge pump circuit of the tag. The imaginary (reactive) component is controlled by connecting one or more reactive elements of an antenna tuning circuit to the antenna. The real component is controlled by a first digital control loop that automatically activates successive taps on a charge pump of the RFID tag which effectively controls the resistance seen by the antenna. A second digital control loop controls the connection of the various reactive components.

Claims

1. An RFID tag having self tuning, comprising:

a charge pump having multiple taps;

an antenna;

an antenna tuning circuit including a plurality of reactive components selectively connectable to the antenna;

a first digital control loop configured to cause the RFID tag to cycle through successive taps until a predetermined criteria has been met;

a second digital control loop configured to control connection of the reactive components to the antenna; and

means indicating to the second digital control loop a status of the first digital control loop.

2. An RFID tag according to claim 1 wherein the predetermined criteria is a maximum voltage at a predetermined point.

3. An RFID tag according to claim 1 wherein the reactive components are capacitors.

4. An RFID tag according to claim 1 wherein the reactive components are inductors.

5. An RFID tag according to claim 1 further comprising:

an RFI) tag main storage capacitor configured to collect and store power from the charge pump and provide power to the RFID tag for its operation; and

means for connecting the main storage capacitor in circuit when a second predetermined criteria has been met.

6. An RFID tag according to claim 5 wherein the second predetermined criteria is a voltage exceeding a predetermined level.

7. A method of operating an RFID tag so that it self-tunes, the RFID tag including a charge pump having multiple taps, an antenna, an antenna tuning circuit including a plurality of reactive components selectively connectable to the antenna, a first digital control loop configured to cause the RFID tag to cycle through successive charge pump taps until a predetermined criteria has been met, a second digital control loop configured to control connection of the reactive components to the antenna, and means indicating to the second digital control loop a status of the first digital control loop, the method comprising:

(a) receiving power at the antenna;

(b) initializing a tuning circuit to a first level of reactance;

(c) initializing a charge pump to operate at a first tap;

(d) determining whether a tuning circuit voltage is greater than a predetermined threshold voltage;

(e) if at step (d) the tuning circuit voltage is greater than the predetermined threshold, banking in a main capacitor of the RFID tag and operating the RFID tag in a normal operation mode; and

(f) if at step (d) the tuning circuit voltage is not greater than the predetermined threshold, controlling the taps of the charge pump and the tuning circuit using said digital loops to increase the tuning circuit voltage.