Passive RFID tags with integrated circuits using sub-threshold technology

1. A method for operating a Radio Frequency Identification (“RFID”) transponder, comprising:

performing energy harvesting operations by a voltage scavenging device of the RFID transponder to collect energy from a Radio Frequency (“RF”) field and store the energy in an energy storage device of the voltage scavenging device;

causing a switch to change positions, when the energy storage device is charged to a pre-determined voltage level, from

(A) a first position in which a closed circuit is formed between an antenna and the voltage scavenging device, and

(B) a second position in which (i) an open circuit is formed between the antenna and the voltage scavenging device and (ii) a closed circuit is formed between the antenna and a transceiver circuit of the RFID transponder;

increasing or decreasing, by a voltage converter of the RFID transponder, a voltage level of a signal received from the voltage scavenging device to a sub-threshold voltage level that is at least one order of magnitude below a normal operating range for the RFID transponder; and

supplying an operating voltage at the sub-threshold voltage level to at least the transceiver circuit.

2. The method according to claim 1 , wherein the normal operating range for a voltage level is 1.2 Volts to 3.6 Volts.

3. The method according to claim 1 , wherein the energy harvesting operations involve:

capturing RF energy emitted within a surrounding environment from equipment;

passing the RF energy through the switch;

converting the RF energy into direct current for generating electric power;

supplying the electric power to the energy storage device for charging the energy storage device to a pre-determined voltage level; and

supplying power from the energy storage device to a controller of the RFID transponder when a voltage level of the energy storage device is equal to or greater than the pre-determined voltage level.

4. The method according to claim 3 , wherein the energy storage device comprises a super capacitor.

5. The method according to claim 3 , further comprising generating and sending a switch control signal from the controller to the switch to cause the switch to change positions.

6. The method according to claim 3 , further comprising communicating information from the RFID transponder to an external device.

7. The method according to claim 6 , wherein the information is useful for determining whether to grant or deny a person access to a restricted area.

8. A method for operating a Radio Frequency Identification (“RFID”) transponder, comprising:

performing energy harvesting operations by a voltage scavenging device of the RFID transponder to collect energy from a Radio Frequency (“RF”) field, magnetic field, heat, light or movement of the RFID transponder;

increasing or decreasing, by a voltage converter of the RFID transponder, a voltage level of a signal received from the voltage scavenging device to a sub-threshold voltage level that is at least one order of magnitude below a normal operating range for the RFID transponder; and

supplying an operating voltage at the sub-threshold voltage level to at least a transceiver circuit of the RFID transponder;

wherein the sub-threshold voltage level is within 200 milli-Volts to 600 milli-Volts.

9. A method for operating a Radio Frequency Identification (“RFID”) transponder, comprising:

performing energy harvesting operations by a voltage scavenging device of the RFID transponder to collect energy from a Radio Frequency (“RF”) field, magnetic field, heat, light or movement of the RFID transponder;

increasing or decreasing, by a voltage converter of the RFID transponder, a voltage level of a signal received from the voltage scavenging device to a sub-threshold voltage level that is at least one order of magnitude below a normal operating range for the RFID transponder; and

supplying an operating voltage at the sub-threshold voltage level to at least a transceiver circuit of the RFID transponder;

wherein the voltage level is increased to the sub-threshold voltage level when the energy is collected from the RF Field, magnetic field, heat or light.

10. A method for operating a Radio Frequency Identification (“RFID”) transponder, comprising:

performing energy harvesting operations by a voltage scavenging device of the RFID transponder to collect energy from a Radio Frequency (“RF”) field, magnetic field, heat, light or movement of the RFID transponder;

increasing or decreasing, by a voltage converter of the RFID transponder, a voltage level of a signal received from the voltage scavenging device to a sub-threshold voltage level that is at least one order of magnitude below a normal operating range for the RFID transponder; and

supplying an operating voltage at the sub-threshold voltage level to at least a transceiver circuit of the RFID transponder;

wherein the voltage level is decreased to the sub-threshold voltage level when the energy is collected from light or movement of the RFID transponder.

11. A Radio Frequency Identification (“RFID”) transponder, comprising:

a voltage scavenging device that performs energy harvesting operations to collect energy from a Radio Frequency (“RF”) field and store the energy in an energy storage device of the voltage scavenging device;

a switch that is caused to change positions, when the energy storage device is charged to a pre-determined voltage level, from

(A) a first position in which a closed circuit is formed between an antenna and the voltage scavenging device, and

(B) a second position in which (i) an open circuit is formed between the antenna and the voltage scavenging device and (ii) a closed circuit is formed between the antenna and a transceiver circuit; and

a voltage converter that increases or decreases a voltage level of a signal received from the voltage scavenging device to a sub-threshold voltage level that is at least one order of magnitude below a normal operating range for the RFID transponder;

wherein the transceiver circuit is supplied an operating voltage at the sub-threshold voltage level.

12. The RFID transponder according to claim 11 , wherein the normal operating range for a voltage level is 1.2 Volts to 3.6 Volts.

13. The RFID transponder according to claim 11 , wherein the energy harvesting operations involve:

capturing RF energy emitted within a surrounding environment from equipment;

passing the RF energy through the switch;

converting the RF energy into direct current for generating electric power;

supplying the electric power to the energy storage device for charging the energy storage device to a pre-determined voltage level; and

supplying power from the energy storage device to a controller of the RFID transponder when a voltage level of the energy storage device is equal to or greater than the pre-determined voltage level.

14. The RFID transponder according to claim 13 , wherein the energy storage device comprises a super capacitor.

15. The RFID transponder according to claim 13 , further comprising a controller that generates and sends a switch control signal to the switch to cause the switch to change positions.

16. The RFID transponder according to claim 13 , wherein the transceiver circuit communicates information to an external device when the operating voltage is supplied thereto at the sub-threshold voltage level.

17. The RFID transponder according to claim 16 , wherein the information is useful for determining whether to grant or deny a person access to a restricted area.

18. A Radio Frequency Identification (“RFID”) transponder, comprising:

a voltage scavenging device that performs energy harvesting operations to collect energy from a Radio Frequency (“RF”) field, magnetic field, heat, light or movement of the RFID transponder;

a voltage converter that increases or decreases a voltage level of a signal received from the voltage scavenging device to a sub-threshold voltage level that is at least one order of magnitude below a normal operating range for the RFID transponder; and

a transceiver circuit that is supplied an operating voltage at the sub-threshold voltage level;

wherein the sub-threshold voltage level is within 200 milli-Volts to 600 milli-Volts.

19. A Radio Frequency Identification (“RFID”) transponder, comprising:

a voltage scavenging device that performs energy harvesting operations to collect energy from a Radio Frequency (“RF”) field, magnetic field, heat, light or movement of the RFID transponder;

a voltage converter that increases or decreases a voltage level of a signal received from the voltage scavenging device to a sub-threshold voltage level that is at least one order of magnitude below a normal operating range for the RFID transponder; and

a transceiver circuit that is supplied an operating voltage at the sub-threshold voltage level;

wherein the voltage level is increased to the sub-threshold voltage level when the energy is collected from the RF Field, magnetic field, heat or light.

20. A Radio Frequency Identification (“RFID”) transponder, comprising:

a voltage scavenging device that performs energy harvesting operations to collect energy from a Radio Frequency (“RF”) field, magnetic field, heat, light or movement of the RFID transponder;

a voltage converter that increases or decreases a voltage level of a signal received from the voltage scavenging device to a sub-threshold voltage level that is at least one order of magnitude below a normal operating range for the RFID transponder; and

a transceiver circuit that is supplied an operating voltage at the sub-threshold voltage level;

wherein the voltage level is decreased to the sub-threshold voltage level when the energy is collected from light or movement of the RFID transponder.