Abstract: Methods and apparatuses for secure communications of confidential information are provided. In an embodiment, a method of communicating with a population of radio frequency identification tags includes transmitting a first interrogation signal, receiving a response to the first interrogation signal from at least one RFID tag at a first received signal strength including at least a portion of a first identification code, and transmitting a second interrogation signal that includes a request for confidential information, a command to transmit a response to the second interrogation signal at a secure power level, and the first identification code. In another embodiment, a method for communicating with an RFID tag includes receiving an interrogation signal that includes a request for confidential information and transmitting a response to the interrogation signal at a secure power level. The response includes the confidential information.

Abstract: Methods, systems, and apparatuses for detecting a reader signal strength in a radio frequency identification (RFID) tag is described. A tag is configured to monitor an attribute of a reader transmitted signal, such as the signal strength. The tag generates an indication of the signal attribute, and transmits the indication of the signal attribute to the reader.

Abstract: Methods, systems, and apparatuses for monitoring and refreshing data stored in radio frequency identification (RFID) tags are described. A voltage margin for data stored in memory of a tag is checked. If the voltage margin has decreased to an undesirable level, the data stored in the tag is refreshed.

Abstract: Methods and apparatuses for secure communications of confidential information are provided. In an embodiment, a method of communicating with a population of radio frequency identification tags includes transmitting a first interrogation signal, receiving a response to the first interrogation signal from at least one RFID tag at a first received signal strength including at least a portion of a first identification code, and transmitting a second interrogation signal that includes a request for confidential information, a command to transmit a response to the second interrogation signal at a secure power level, and the first identification code. In another embodiment, a method for communicating with an RFID tag includes receiving an interrogation signal that includes a request for confidential information and transmitting a response to the interrogation signal at a secure power level. The response includes the confidential information.

Abstract: Methods, systems, and apparatuses for preventing unauthorized reading of data stored in tags are described. A non-identifying bit pattern, an identifying bit pattern, and a first passcode are stored in the tag. A read lock command is received by the tag. The tag determines whether a second passcode associated with the read lock command matches the first passcode. Read access to the identifying bit pattern is disabled if it is determined that the second passcode matches the first passcode.

Abstract: Methods, systems, and apparatuses for detecting a reader signal strength in a radio frequency identification (RFID) tag is described. A tag is configured to monitor an attribute of a reader transmitted signal, such as the signal strength. The tag generates an indication of the signal attribute, and transmits the indication of the signal attribute to the reader.

Abstract: Methods, systems, and apparatuses for testing antenna(s) of a radio frequency identification (RFID) tag are described. A reader transmits a test command signal to a RFID tag having a plurality of antennas. Each antenna of the plurality of antennas is coupled to a respective antenna port. The tag processes the test command signal to determine which one or more of the plurality of antennas is to be tested. The tag couples an information signal to the antenna port(s) corresponding with the antenna(s) to be tested. For example, the tag may include enabling elements that selectively couple the information signal to respective antenna ports based on respective test control signals. The RFID tag generates the test control signals based on the test command signal. The reader awaits receipt of the information signal from the RFID tag.

Abstract: Methods, systems, and apparatuses for monitoring and refreshing data stored in radio frequency identification (RFID) tags are described. A voltage margin for data stored in memory of a tag is checked. If the voltage margin has decreased to an undesirable level, the data stored in the tag is refreshed.

Abstract: An ac input voltage is fed to one input of a multiplier serving phase comparator of a phase-locked loop. The output voltage of the VCO feeding the second input of the phase comparator to lock the frequency has a &pgr;/4 phase shift with respect to the input voltage. When two such phase locked loops are connected in tandem, a &pgr;/2 quadrature voltage is obtained. When more than two phase-locked loops are connected in tandem, any multiples of &pgr;/4 phase shift can be obtained.