Method and apparatus for sensing environment using a wireless passive sensor
A method for execution by a RFID tag includes receiving, by an antenna of the RFID tag, an RF signal from an RFID reader, where the RF signal has a carrier frequency. The method further includes determining, by a tuning circuit of the RFID tag, a received power level of the RF signal at the carrier frequency and whether the received power level compares favorably to a power level threshold. When the received power level compares unfavorably to the power level threshold, the method further includes adjusting, by the tuning circuit, the input impedance of the RFID tag by adjusting a tank circuit of the RFID tag until the received power level compares favorably to the power level threshold, where the input impedance of the RFID tag is based on one or more of impedance of the antenna and impedance of the tank circuit.
1. A radio frequency identification (RFID) tag comprises:
an antenna operable to receive a radio frequency (RF) signal, wherein the RF signal has a carrier frequency of a plurality of carrier frequencies, wherein the plurality of carrier frequencies spans a broad frequency band;
a tank circuit coupled to the antenna, wherein an input impedance of the RFID tag is based on one or more of impedance of the antenna and impedance of the tank circuit; and
a tuning circuit operable to:
determine a received power level of the RF signal at the carrier frequency;
determine whether the received power level compares favorably to a power level threshold; and
when the received power level compares unfavorably to the power level threshold, adjust the input impedance of the RFID tag by adjusting the tank circuit until the received power level compares favorably to the power level threshold.
2. The RFID tag of claim 1 , wherein the threshold power level corresponds to a power level that occurs when the carrier frequency is substantially equal to a resonant frequency of at least one of the antenna and the tank circuit.
3. The RFID tag of claim 1 , wherein the tuning circuit includes a processing module.
4. The RFID tag of claim 1 further comprises:
the antenna is further operable to receive an input command from an RFID reader; and
the tuning circuit is further operable to:
determine a required power level to complete the input command; and
set the required power level as the power level threshold.
5. The RFID tag of claim 1 , wherein the tank circuit comprises:
an inductor; and
a variable capacitor, wherein the tuning circuit is operable to adjust the variable capacitor.
6. The RFID tag of claim 1 , wherein the tank circuit comprises:
a capacitor; and
a variable inductor, wherein the tuning circuit is operable to adjust the variable inductor.
7. The RFID tag of claim 1 further comprises:
a regulator operable to convert the received RF signal into a power supply voltage that powers the tuning circuit.
8. The RFID tag of claim 1 , wherein the tuning circuit comprises:
a reference circuit operable to generate a power reference of the received RF signal;
a comparison circuit operable to compare a current power reference of a current power level of the received RF signal with the power level threshold; and
control signal circuit operable to generate a control signal based on the comparing of the current power reference with the power level threshold.
9. A method for execution by a radio frequency identification (RFID) tag, the method comprises:
receiving, by an antenna of the RFID tag, a radio frequency (RF) signal from an RFID reader, wherein the RF signal has a carrier frequency of a plurality of carrier frequencies, wherein the plurality of carrier frequencies spans a broad frequency band;
determining, by a tuning circuit of the RFID tag, a received power level of the RF signal at the carrier frequency;
determining, by the tuning circuit, whether the received power level compares favorably to a power level threshold; and
when the received power level compares unfavorably to the power level threshold, adjusting, by the tuning circuit, the input impedance of the RFID tag by adjusting a tank circuit of the RFID tag until the received power level compares favorably to the power level threshold, wherein the tank circuit is coupled to the antenna, and wherein the input impedance of the RFID tag is based on one or more of impedance of the antenna and impedance of the tank circuit.
10. The method of claim 9 , wherein the threshold power level corresponds to a power level that occurs when the carrier frequency is substantially equal to a resonant frequency of at least one of the antenna and the tank circuit.
11. The method of claim 9 , wherein the tuning circuit includes a processing module.
12. The method of claim 9 further comprises:
receiving, by the antenna, an input command from the RFID reader;
determining, by the tuning circuit, a required power level to complete the input command; and
setting, by the tuning circuit, the required power level as the power level threshold.