Self tuning RFID
First Claim
Patent Images
1. An RFID tag having self tuning, comprising:
- a charge pump having multiple taps;
an antenna;
an antenna impedance matching circuit coupled to the antenna and including a plurality of reactive components that are selectively connectable to the antenna;
a first digital control loop configured to cause the RFID tag to cycle through successive taps of the charge pump to control a resistive impedance match for the antenna and a charge pump output voltage;
a second digital control loop configured to increase the charge pump output voltage by controlling connection of the reactive components to the antenna and a reactive impedance match for the antenna; and
an indicator to the second digital control loop indicating a status of the first digital control loop cycle, wherein the reactive components of the antenna impedance matching circuit are connected to the antenna in response to the indication.
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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.
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Citations
15 Claims
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1. An RFID tag having self tuning, comprising:
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a charge pump having multiple taps; an antenna; an antenna impedance matching circuit coupled to the antenna and including a plurality of reactive components that are selectively connectable to the antenna; a first digital control loop configured to cause the RFID tag to cycle through successive taps of the charge pump to control a resistive impedance match for the antenna and a charge pump output voltage; a second digital control loop configured to increase the charge pump output voltage by controlling connection of the reactive components to the antenna and a reactive impedance match for the antenna; and an indicator to the second digital control loop indicating a status of the first digital control loop cycle, wherein the reactive components of the antenna impedance matching circuit are connected to the antenna in response to the indication. - View Dependent Claims (2, 3, 4, 5, 6, 8, 9, 10, 11, 12)
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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 impedance matching 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 to produce a charge pump output voltage, a second digital control loop configured to control connection of the reactive components to the antenna, and an indicator to the second digital control loop indicating a status of the first digital control loop cycle, the method comprising:
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(a) receiving power at the antenna; (b) initializing the antenna impedance matching circuit to a first level of reactance; (c) initializing a charge pump to provide a first level of resistive impedance match for the antenna and operate at a first tap; (d) determining whether a charge pump output voltage is greater than a predetermined threshold voltage; (e) if at step (d) the charge pump output 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 charge pump output voltage is not greater than the predetermined threshold then, using said digital loops, cycling through one or more taps of the charge pump to provide successive levels of resistive impedance match for the antenna, and based on the cycling through the one or more taps of the charge pump, connecting the reactive components of the antenna impedance matching circuit to adjust a reactive impedance match for the antenna and increase the charge pump output voltage. - View Dependent Claims (13, 14, 15)
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Specification