Pressure based wireless sensor and applications thereof
A radio frequency identification (RFID) tag includes an antenna, an analog front end, a processing circuit, and memory. The analog front end includes a power circuit, a tuning circuit, a transmitter, and a receiver. The power circuit is operably coupled to convert a radio frequency (RF) signal into a power supply voltage. The tuning circuit, when enabled, adjusts an RF characteristic of the analog front end to tune power harvesting from the RF signal. The transmitter is operably coupled to transmit a response signal to the RFID reader via the antenna. The receiver is operably coupled to receive a command signal from the RFID reader, wherein the command signal is contained within a portion of the RF signal. The processing circuit is operable to interpret the command signal and generate the response signal.
1. A passive radio frequency (RF) circuit comprises:
antenna circuitry including an antenna and a tuning circuit, wherein the antenna circuitry is operably coupled to:
receive an inbound RF signal via an inbound propagating electromagnetic wave; and
transmit an outbound RF signal via an outbound propagating electromagnetic wave;
a power harvesting circuit operably coupled to generate a supply voltage from the inbound RF signal;
a temperature sensor operable to, when the supply voltage is generated, generate a digital signal that represents a temperature;
a processing module operable to, when the supply voltage is generated, process the digital signal to produce a digital representation of the temperature; and
an RF transmitter operable to, when the supply voltage is generated, transmit, via the antenna circuitry, the outbound RF signal that includes the digital representation of the temperature.
2. The passive RF circuit of claim 1 , wherein the temperature sensor is further operable to:
generate the digital signal as a representation of an electrical characteristic of the temperature sensor, wherein, as the temperature changes, the electrical characteristic of the temperature sensor changes.
3. The passive RF circuit of claim 1 , wherein the processing module is further operable to:
interpret the digital signal to establish a value of the electrical characteristic; and
processing the value of the electrical characteristic to produce the digital representation of the temperature.
4. The passive RF circuit of claim 1 further comprises:
as the temperature changes, an electrical characteristic of the temperature sensor changes;
the change of the electrical characteristic causes a change in an RF characteristic of antenna circuitry; and
the processing module is further operable to process the change of the RF characteristic of the antenna circuitry as the digital signal that represents a temperature.
5. The passive RF circuit of claim 4 , wherein the processing module is further operable to processing the change of the RF characteristic by:
detecting a variance of the RF characteristic from a desired value; and
processing the variance to generate the digital representation of the temperature.
6. The passive RF circuit of claim 1 further comprises:
the processing module generating a sense temperature command in response to a message of inbound RF signal; and
in response to the sense temperature command, the temperature sensor generates the digital signal that represents a temperature.
7. The passive RF circuit of claim 1 further comprises:
memory operable to store the digital representation of the temperature.
8. The passive RF circuit of claim 1 , wherein the processing module is further operable to:
receive the digital signal that represents a known temperature;
produce the digital representation of the known temperature from the digital signal; and
unitize the digital representation of the known temperature for calibration.
9. The passive RF circuit of claim 1 , wherein the processing module is further operable to produce the digital representation of the temperature by one of:
converting the digital signal into a coded value; and
converting the digital signal or the coded value into a temperature value.
10. The passive RF circuit of claim 1 further comprises:
the processing module is further operable to generate a temperature request in accordance with a request of the inbound RF signal; and
the temperature sensor generate the digital signal that represents a temperature in response to the temperature request.
11. The passive RF circuit of claim 1 further comprises:
a moisture sensor operable to, when the supply voltage is generated, generate a second signal that represents a moisture level; and
the processing module operable to, when the supply voltage is generated, process the second signal to produce a second digital representation of the moisture level.
12. The passive RF circuit of claim 11 , wherein the processing module is further operable to:
generate a third digital representation for humidity based on the digital representation of the temperature and the second digital representation of the moisture level.
13. A radio frequency (RF) circuit comprises:
antenna circuitry including an antenna and a tuning circuit, wherein the antenna circuitry is operably coupled to:
receive an inbound RF signal via an inbound propagating electromagnetic wave; and
transmit an outbound RF signal via an outbound propagating electromagnetic wave;
a temperature sensor operable to generate a digital signal that represents a temperature;
a processing module operable to process the digital signal to produce a digital representation of the temperature; and
an RF transmitter operable to transmit, via the antenna circuitry, the outbound RF signal that includes the digital representation of the temperature.
14. The RF circuit of claim 13 , wherein the temperature sensor is further operable to:
generate the digital signal as a representation of an electrical characteristic of the temperature sensor, wherein, as the temperature changes, the electrical characteristic of the temperature sensor changes.
15. The RF circuit of claim 13 , wherein the processing module is further operable to:
interpret the digital signal to establish a value of the electrical characteristic; and
processing the value of the electrical characteristic to produce the digital representation of the temperature.
16. The RF circuit of claim 13 further comprises:
as the temperature changes, an electrical characteristic of the temperature sensor changes;
the change of the electrical characteristic causes a change in an RF characteristic of antenna circuitry; and
the processing module is further operable to process the change of the RF characteristic of the antenna circuitry as the digital signal that represents a temperature.
17. The RF circuit of claim 16 , wherein the processing module is further operable to processing the change of the RF characteristic by:
detecting a variance of the RF characteristic from a desired value; and
processing the variance to generate the digital representation of the temperature.
18. The RF circuit of claim 13 further comprises:
the processing module generating a sense temperature command in response to a message of inbound RF signal; and
in response to the sense temperature command, the temperature sensor generates the digital signal that represents a temperature.
19. The RF circuit of claim 13 further comprises:
memory operable to store the digital representation of the temperature.
20. The RF circuit of claim 13 , wherein the processing module is further operable to:
receive the digital signal that represents a known temperature;
produce the digital representation of the known temperature from the digital signal; and
unitize the digital representation of the known temperature for calibration.
21. The RF circuit of claim 13 , wherein the processing module is further operable to produce the digital representation of the temperature by one of:
converting the digital signal into a coded value; and
converting the digital signal or the coded value into a temperature value.
22. The RF circuit of claim 13 further comprises:
the processing module is further operable to generate a temperature request in accordance with a request of the inbound RF signal; and
the temperature sensor generate the digital signal that represents a temperature in response to the temperature request.
23. The RF circuit of claim 13 further comprises:
a moisture sensor operable to generate a second signal that represents a moisture level; and
the processing module operable to process the second signal to produce a second digital representation of the moisture level.
24. The RF circuit of claim 23 , wherein the processing module is further operable to:
generate a third digital representation for humidity based on the digital representation of the temperature and the second digital representation of the moisture level.