LOW POWER RADIO FREQUENCY COMMUNICATION

• US 20140062672A1
• Filed: 03/05/2013
• Published: 03/06/2014
• Est. Priority Date: 04/05/2012
• Status: Active Grant

• Current Assignee: Jonathan J. Hull, Ken Gudan, Matthew S. Reynolds, Sergey Chemishkian
• Original Assignee: Jonathan J. Hull, Ken Gudan, Matthew S. Reynolds, Sergey Chemishkian
• Inventors: Chemishkian, Sergey, Hull, Jonathan J., Reynolds, Matthew S., Gudan, Ken
• Granted Patent: US 9,754,202 B2
• Time in Patent Office: Days
• US Class Current: 340/10.33
• CPC Class Codes: G06K 19/0715 the arrangement including means to regulate power transfer to the integrated circuit
• 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: Y02D 30/70 in wireless communication networks

Abstract

A method, system and tag for low power radio frequency communication is described. In one embodiment, the RF tag comprises: an access point coupled to provide access to a network; an RF tag comprising an energy harvesting unit operable to convert incident RF energy to direct current (DC); a storage unit operable to store recovered DC power; a passive wakeup pattern detector operable to generate an interrupt in response to detecting a set of one or more subcarriers; one or more sensors for sensing; a communication mechanism; and a microcontroller coupled to the energy harvesting and storage units, the one or more sensors, and the backscatter communicator, the microcontroller operable to wake up from a sleep state in response to the interrupt and cause the communication mechanism to exchange data wirelessly with another while powered by energy previously harvested and stored by the energy harvesting and storage unit.

Claims

1. A communication system comprising:

an access point coupled to provide access to a network;

an RF tag comprising

an energy harvesting unit operable to convert incident RF energy to direct current (DC);

a storage unit operable to store recovered DC power;

a passive wakeup pattern detector operable to generate an interrupt in response to detecting a set of one or more subcarriers;

one or more sensors for sensing;

a communication mechanism; and

a microcontroller coupled to the energy harvesting and storage units, the one or more sensors, and the backscatter communicator, the microcontroller operable to wake up from a sleep state in response to the interrupt and cause the communication mechanism to exchange data wirelessly with another while powered by energy previously harvested and stored by the energy harvesting and storage unit.

2. The communication system defined in claim 1 wherein the passive wakeup pattern detector comprises a frequency-based wakeup detector.

3. The communication system defined in claim 2 wherein the frequency-based wakeup detector comprises:

a threshold detector; and

a pattern detector coupled to the threshold detector.

4. The communication system defined in claim 3 wherein the threshold detector looks at RF power in a sub-band of subcarrier frequencies and generates a wake-up interrupt to wake up the microcontroller if the RF power exceeds a power threshold.

5. The communication system defined in claim 3 wherein the pattern detector comprises:

a set of narrow band-pass filters tuned to a set of subcarrier frequencies; and

a plurality of threshold detectors, each threshold detector being coupled to a distinct one of the band-pass filters.

6. The communication system defined in claim 5 wherein the pattern detector further comprises a Boolean function, and wherein the pattern detector is operable to listen on the set of subcarrier frequencies, construct a logical Boolean vector for the set of subcarriers based on a relationship between a subcarrier and a power threshold, and use the Boolean function for a specified time as a wakeup condition.

7. The communication system defined in claim 3 wherein the threshold detector comprises:

a bandpass filter having an output, the filter operable to filter a received RF signal to obtain a filtered RF signal with a set of subcarrier frequencies, the filtered RF signal being output on the output of the bandpass filter;

an envelope detector having an input coupled to the output of the bandpass filter and being operable to output an RF envelope of the filtered RF signal; and

a comparator having first and second inputs and an output, wherein the first input is coupled an output of the envelope detector and the second input coupled to a power threshold, the comparator is operable to output a pattern detector wake-up signal to wake up the pattern detector when the RF envelope exceeds the power threshold.

8. The communication system defined in claim 3 wherein the pattern detector comprises:

a n-way RF splitter operable to feed RF signals;

n parallel detector branches coupled to receive the RF signals fed from the n-way RF splitter, wherein each branch of the n parallel detector branches including

a bandpass filter tuned to a subcarrier frequency to generate a filtered signal,

an envelope detector coupled to receive the filtered signal and generate an RF envelope, and

a comparator to compare the RF envelope to a power threshold and generate a comparator output;

a Boolean logic block to receive comparator outputs from each branch of the n parallel detector branches and generate a wake-up interrupt based on the comparator outputs.

9. The communication system defined in claim 1 wherein the communication mechanism comprises a radio.

10. The communication system defined in claim 1 wherein the communication mechanism comprises a backscatter communicator.

11. A method for communicating information wirelessly between an access point and a tag, the method comprising:

monitoring, by the tag, RF communications with the tag while converting incident RF energy to direct current using an energy harvesting unit of the tag;

sending, by the access point, an RF signal to the tag;

detecting one or more subcarriers in the RF communications using a passive wakeup pattern detector in the tag;

generating an interrupt to a microcontroller in the tag in response to detecting the one or more subcarriers;

waking up the microcontroller in response to the interrupt to cause the communication mechanism to exchange data wirelessly with another device while powered by energy previously harvested and stored by the energy harvesting and storage unit; and

communicating information between the tag and the access point.

12. The method defined in claim 11 wherein detecting one or more subcarriers in the RF communications using a passive wakeup pattern detector in the tag is performed using a frequency-based wakeup detector.

13. The method defined in claim 12 wherein the frequency-based wakeup detector comprises:

a threshold detector; and

a pattern detector coupled to the threshold detector.

14. The method defined in claim 13 further comprising the threshold detector looking at RF power in a sub-band of subcarrier frequencies and generating a wake-up interrupt to wake up the microcontroller if the RF power exceeds a power threshold.

15. The method defined in claim 13 further comprising:

filtering the RF communications using a set of narrow bandpass filters tuned to a set of subcarrier frequencies; and

using a plurality of threshold detectors to performing threshold detection on outputs of the bandpass filters.

16. The method defined in claim 15 wherein the pattern detector further comprises a Boolean function, and further comprising listening on the set of subcarrier frequencies, constructing a logical Boolean vector for the set of subcarriers based on a relationship between a subcarrier and a power threshold, and using the Boolean function for a specified time as a wakeup condition.

17. The method defined in claim 13 further comprising:

filtering a received RF signal using a bandpass filter having an output to obtain a filtered RF signal with a set of subcarrier frequencies, including outputting the filtered RF signal on the output of the bandpass filter;

performing envelope detection using an envelope detector, having an input coupled to the output of the bandpass filter, to output an RF envelope of the filtered RF signal; and

comparing the RF envelope to a power threshold using a comparator having first and second inputs and an output and outputting a pattern detector wake-up signal to wake up the pattern detector when the RF envelope exceeds the power threshold.

18. The method defined in claim 13 further comprising:

generating a plurality of RF signals using a n-way RF splitter;

for each of the plurality of RF signals,

filtering each RF signal using a bandpass filter tuned to a subcarrier frequency to generate a filtered signal,

performing envelope detection to generate an RF envelope using an envelope detector coupled to receive the filtered signal, and

comparing the RF envelope to a power threshold to generate a comparator output; and

generating a wake-up interrupt based on received comparator outputs.