RFID DETECTION SYSTEM

1 . An RFID detection system, comprising:

a detection circuit configured to detect the presence of one or more RFID devices near the RFID detection system, wherein the detection circuit comprises an oscillating circuit, and wherein the detection circuit is configured to:

hold the RFID detection system in a low power mode in which the RFID detection system is configured to not actively attempt to communicate with nearby RFID devices;

monitor one or more parameters of a signal of the oscillating circuit;

compare the one or more monitored parameters to one or more reference parameters; and

based on the comparison, determine whether to transition the RFID detection system from the low power mode into an active communication mode in which the RFID detection system is configured to actively attempt to communicate with nearby RFID devices.

2 . The RFID detection system of claim 1 , wherein:

the oscillating circuit has an operating frequency and comprises a sense antenna having a resonant frequency that is tuned to be higher than the operating frequency,

the one or more monitored parameters comprise a voltage of the oscillating circuit,

comparing the one or more monitored parameters to one or more reference parameters comprises detecting a decrease in the voltage of the oscillating circuit, wherein a decrease in the voltage is indicative of the presence of an RFID device near the RFID detection system, and

when a decrease in the voltage is detected, the detection circuit is configured to switch the RFID detection system from the low power mode into the active communication mode.

3 . The RFID detection system of claim 1 , wherein the one or more monitored parameters comprise one or more frequencies of one or more signal components for a voltage signal in the detection circuit.

4 . The RFID detection system of claim 3 , wherein the one or more RFID devices have a resonant frequency, and wherein the detection circuit is configured to:

sweep an operating frequency of the detection circuit across a range of frequencies, the range of frequencies including the resonant frequency of the one or more RFID devices, wherein the sweeping is performed at a sweep frequency;

monitor the voltage signal in the detection circuit to determine whether the voltage signal includes a signal component having a frequency of approximately twice the sweep frequency; and

when it is determined that the voltage signal includes a signal component having a frequency of approximately twice the sweep frequency, switch the RFID detection system from the low power mode into the active communication mode.

5 . The RFID detection system of claim 4 , wherein the detection circuit is configured to estimate a relative distance between the RFID detection system and one of the one or more RFID devices based on a magnitude of the signal component having the frequency of approximately twice the sweep frequency.

6 . The RFID detection system of claim 3 , wherein the one or more RFID devices have a resonant frequency, and wherein the detection circuit is configured to:

sweep an operating frequency of the detection circuit across a range of frequencies, the range of frequencies including the resonant frequency of the one or more RFID devices, wherein the sweeping is performed at a sweep frequency;

identify a component of the voltage signal in the detection circuit having a frequency approximately equal to the sweep frequency;

determine an amplitude of the component of the voltage signal having the frequency approximately equal to the sweep frequency;

compare the determined amplitude to a reference voltage level; and

when the amplitude is greater than the reference voltage level, switch the RFID detection system from the low power mode into the active communication mode.

7 . The RFID detection system of claim 3 , wherein the detection circuit is configured to sweep an operating frequency of the detection circuit across a range of frequencies, and wherein the detection circuit is configured such that the presence of one or more RFID devices near the RFID detection system causes a substantial change in the voltage signal near a resonant frequency of the one or more RFID devices and one or more objects other than the one or more RFID devices cause a change in the voltage signal across the range of frequencies.

8 . The RFID detection system of claim 1 , wherein, in the low power sleep mode, the detection circuit draws a current between 1 μA and 25 μA from an energy storage device of the RFID detection system.

9 . An RFID detection system, comprising:

an oscillating circuit having an operating frequency, the oscillating circuit comprising a sense antenna having a resonant frequency that is tuned to be higher than the operating frequency; and

a detection circuit configured to monitor a voltage of the oscillating circuit, wherein a decrease in the voltage is indicative of the presence of an RFID device near the RFID detection system, and wherein, when the voltage decreases, the detection circuit is configured to switch the RFID detection system from a low power mode into an active communication mode.

10 . The RFID detection system of claim 9 , wherein, in the low power sleep mode, the detection circuit draws a current between 1 μA and 25 μA from an energy storage device of the RFID detection system.

11 . The RFID detection system of claim 9 , wherein the detection circuit is configured to sense a source of stray capacitance near the RFID detection system when the voltage of the oscillating circuit increases.

12 . The RFID detection system of claim 9 , wherein the oscillating circuit comprises a crystal locked oscillator.

13 . A method, comprising:

holding an RFID detection system in a low power mode in which the RFID detection system is configured to not actively attempt to communicate with nearby RFID devices, wherein the RFID detection system comprises an oscillating circuit;

monitoring one or more parameters of a signal of the oscillating circuit;

comparing the one or more monitored parameters to one or more reference parameters; and

based on the comparison, determining whether to transition the RFID detection system from the low power mode into an active communication mode in which the RFID detection system is configured to actively attempt to communicate with nearby RFID devices.

14 . The method of claim 13 , wherein:

the oscillating circuit has an operating frequency and comprises a sense antenna having a resonant frequency that is tuned to be higher than the operating frequency,

the one or more monitored parameters comprise a voltage of the oscillating circuit,

comparing the one or more monitored parameters to one or more reference parameters comprises detecting a decrease in the voltage of the oscillating circuit, a decrease in the voltage being indicative of the presence of an RFID device near the RFID detection system, and

wherein the method further comprises switching the RFID detection system from the low power mode into the active communication mode when a decrease in the voltage is detected.

15 . The method of claim 13 , wherein the one or more monitored parameters comprise one or more frequencies of one or more signal components for a voltage signal in the detection circuit.

16 . The method of claim 15 , wherein the one or more RFID devices have a resonant frequency, and wherein the method further comprises:

sweeping an operating frequency of the detection circuit across a range of frequencies, wherein the range of frequencies includes the resonant frequency of the one or more RFID devices, and wherein the sweeping is performed at a sweep frequency;

monitoring the voltage signal in the detection circuit to determine whether the voltage signal includes a signal component having a frequency of approximately twice the sweep frequency; and

when it is determined that the voltage signal includes a signal component having a frequency of approximately twice the sweep frequency, switching the RFID detection system from the low power mode into the active communication mode.

17 . The method of claim 16 , further comprising estimating a relative distance between the RFID detection system and one of the one or more RFID devices based on a magnitude of the signal component having the frequency of approximately twice the sweep frequency.

18 . The method of claim 15 , wherein the one or more RFID devices have a resonant frequency, and wherein the method further comprises:

sweeping an operating frequency of the detection circuit across a range of frequencies, the range of frequencies including the resonant frequency of the one or more RFID devices, wherein the sweeping is performed at a sweep frequency;

identifying a component of the voltage signal in the detection circuit having a frequency approximately equal to the sweep frequency;

determining an amplitude of the component of the voltage signal having the frequency approximately equal to the sweep frequency;

comparing the determined amplitude to a reference voltage level; and

when the amplitude is greater than the reference voltage level, switching the RFID detection system from the low power mode into the active communication mode.

19 . The method of claim 15 , further comprising sweeping an operating frequency of the detection circuit across a range of frequencies, and wherein the detection circuit is configured such that the presence of one or more RFID devices near the RFID detection system causes a substantial change in the voltage signal near a resonant frequency of the one or more RFID devices and one or more objects other than the one or more RFID devices cause a change in the voltage signal across the range of frequencies.

20 . The method of claim 13 , wherein, in the low power sleep mode, the detection circuit draws a current between 1 μA and 25 μA from an energy storage device of the RFID detection system.