RFID tags enforcing persistence while powered

1. A Radio Frequency Identification (RFID) integrated circuit (IC) configured to selectively deassert an asserted protocol flag that, absent such selective deassertion or a reader command to deassert the asserted protocol flag, would remain asserted while the IC has sufficient power to operate, the IC comprising:

a demodulator block configured to:

detect modulated reader transmissions; and

demodulate reader commands from at least a subset of the modulated reader transmissions; and

a processing block coupled to the demodulator block and configured to:

receive, via the demodulator block, a first reader command;

assert the protocol flag in response to receiving the first reader command; and

while the IC has sufficient power to operate:

determine whether a time interval between detecting a first modulated reader transmission and detecting a second modulated reader transmission exceeds a minimum time; and

if the time interval exceeds the minimum time, then deassert the asserted protocol flag despite the IC having sufficient power to operate.

2. The RFID IC of claim 1 , wherein the processing block is configured to determine that a modulated reader transmission has been detected by determining that an amplitude-modulated RF signal has been detected.

3. The RFID IC of claim 1 , wherein the processing block is configured to determine that a modulated reader transmission has been detected by determining that a reader command has been received.

4. The RFID IC of claim 1 , further comprising a rectifier configured to harvest the sufficient power to operate from RF signals.

5. The RFID IC of claim 4 , wherein the RF signals originate from at least one of a microcell and a picocell.

6. The RFID IC of claim 4 , wherein:

the second modulated reader transmission is in a first radio frequency range; and

the rectifier is configured to harvest power from a non-reader source in a second radio frequency range different from the first radio frequency range.

7. The RFID IC of claim 1 , wherein the minimum time is based on a protocol-specified persistence time for the asserted protocol flag.

8. A Radio Frequency Identification (RFID) integrated circuit (IC) configured to selectively erase stored data that, absent such selective erasing or a reader command to erase the data, would be retained while the IC has sufficient power to operate, the IC comprising:

a memory configured to store the data;

a demodulator block configured to:

detect modulated reader transmissions; and

demodulate reader commands from at least a subset of the modulated reader transmissions; and

a processing block coupled to the memory and the demodulator block and configured to:

receive, via the demodulator block, a first reader command;

store data in the memory in response to receiving the first reader command; and

while the IC has sufficient power to operate:

determine whether a time interval between detecting a first modulated reader transmission and detecting a second modulated reader transmission exceeds a minimum time; and

if the time interval exceeds the minimum time, then erase the stored data despite the IC having sufficient power to operate.

9. The RFID IC of claim 8 , wherein the processing block is configured to determine that a modulated reader transmission has been detected by determining that an amplitude-modulated RF signal has been detected.

10. The RFID IC of claim 8 , wherein the processing block is configured to determine that a modulated reader transmission has been detected by determining that a reader command has been detected.

11. The RFID IC of claim 8 , wherein the stored data is cryptographic state information.

12. The RFID IC of claim 8 , further comprising a rectifier configured to harvest the sufficient power to operate from RF signals.

13. The RFID IC of claim 12 , wherein the RF signals originate from at least one of a microcell and a picocell.

14. The RFID IC of claim 12 , wherein:

the second modulated reader transmission in a first radio frequency range; and

the rectifier is configured to harvest power from a non-reader source in a second radio frequency range different from the first radio frequency range.

15. A Radio Frequency Identification (RFID) integrated circuit (IC) configured to selectively transition between a first and a second operating states whereby, absent such selective transitioning or a reader command to transition states, the IC would remain in the first operating state while the IC has sufficient power to operate, the IC comprising:

a demodulator block configured to:

detect modulated reader transmissions; and

demodulate reader commands from at least a subset of the modulated reader transmissions; and

a processing block coupled to the demodulator block and configured to:

receive, via the demodulator block, a first reader command;

transition to the first operating state in response to receiving the first reader command; and

while the IC has sufficient power to operate:

determine whether a time interval between detecting a first modulated reader transmission and detecting a second modulated reader transmission exceeds a minimum time; and

if the time interval exceeds the minimum time, then transition from the first operating state to the second operating state despite the IC having sufficient power to operate.

16. The RFID IC of claim 15 , wherein the processing block is configured to determine that a modulated reader transmission has been detected by determining that an amplitude-modulated RF signal has been detected.

17. The RFID IC of claim 15 , wherein the processing block is configured to determine that a modulated reader transmission has been detected by determining that a reader command has been detected.

18. The RFID IC of claim 15 , further comprising a rectifier configured to harvest power from RF signals.

19. The RFID IC of claim 18 , wherein the RF signals originate from at least one of a microcell and a picocell.

20. The RFID IC of claim 15 , wherein the first operating state is a private state and the second operating state is a public state in which IC access is more restrictive than in the private state.