Devices and methods for improving voltage handling and/or bi-directionality of stacks of elements when connected between terminals are described. Such devices and method include use of symmetrical compensation capacitances, symmetrical series capacitors, or symmetrical sizing of the elements of the stack.

A system is provided that can automatically adjust a tuned circuit to resonate at the frequency of an applied excitation signal. The error in the resonant frequency of the tuned circuit is determined in real time from signals derived from within the network. The system permits the use of a time varying excitation frequency in a high Q circuit, including modulation conveying information. The tuning information may be stored in a memory and used to set the tuning instantaneously in order to maintain resonance when the excitation frequency changes abruptly, for example when frequency shift keying is used.

A circuit includes a coupling structure and a first inductive device. The coupling structure includes two or more conductive loops and a set of conductive paths electrically connecting the two or more conductive loops. The first inductive device is magnetically coupled with a first conductive loop of the two or more conductive loops.

A wireless sensor includes a radio frequency (RF) receiving circuit including a plurality of components, where impedances of the plurality of components establish a resonant frequency of the RF receiving circuit. The wireless sensor further includes a sensing element that when exposed to an environmental condition, affects the resonant frequency of the RF receiving circuit. The wireless sensor further includes a processing module that is operable to determine a first value for an adjustable element of a plurality of elements for a known environmental condition based on the resonant frequency and the carrier frequency, determine a second value for the adjustable element for an unknown environmental condition based on the resonant frequency and the carrier frequency, and determine a difference between the first and second values that corresponds to a change between the known environmental condition and the unknown environmental condition.

A radio frequency identification (RFID) tag includes an antenna, a power circuit, a tuning circuit, a receiver, and a backscatter transmitter. The power circuit is operably coupled to convert a radio frequency (RF) signal received via the antenna from an RFID reader into one or more power supply voltages. The tuning circuit is operably coupled to the antenna and to adjust an RF characteristic of the antenna and/or the tuning circuit based on a difference between a resonant frequency of the RFID tag and a carrier frequency of the RF signal. The receiver is operably coupled to receive a command signal from the RFID reader. The backscatter transmitter is operably coupled to transmit a response signal to the RFID reader via the antenna.

A method includes receiving, by a radio frequency identification (RFID) tag, a radio frequency (RF) signal from an RFID reader. When the RF signal includes a command, the method further includes interpreting, by the RFID tag, the command to determine a field strength shell of interest. When the RFID tag is in the field strength shell of interest, the method further includes further interpreting, by the RFID tag, the command to determine a type of request, and providing, by the RFID tag, a response regarding the type of request to include one or more of a matched impedance value generated in response to the RF signal, a field strength reference current generated in response to the RF signal, and a digital value representative of an environmental condition.

A method includes receiving, by a radio frequency identification (RFID) receiver, an electromagnetic propagated radio frequency (RF) signal. The method further includes capturing, by a current field strength detector circuit, a first current response of the tuning circuit to received signal strength of the RF signal; varying, by a tuning circuit, the variable capacitor in a first tuning direction; capturing, by the current field strength detector circuit, a second current response of the tuning circuit to the received signal strength of the RF signal; and comparing, by the current field strength detector circuit, the captured first response to the captured second response. When the captured second response is weaker than the captured first response, the method further includes varying, by the tuning circuit, the variable capacitor in a second tuning direction, and adjusting the variable capacitor in the second tuning direction until a substantially maximum received signal strength is reached.

Methods and apparatuses for use in tuning reactance are described. Open loop and closed loop control for tuning of reactances are also described. Tunable inductors and/or tunable capacitors may be used in filters, resonant circuits, matching networks, and phase shifters. Ability to control inductance and/or capacitance in a circuit leads to flexibility in operation of the circuit, since the circuit may be tuned to operate under a range of different operating frequencies.

A circuit includes a first digital controlled oscillator and a second digital controlled oscillator coupled to the first digital controlled oscillator. A skew detector is connected to determine a skew between outputs of the first digital controlled oscillator and the second digital controlled oscillator, and a decoder is utilized to output a control signal, based on the skew, to modify a frequency of the first digital controlled oscillator using a switched capacitor array to reduce or eliminate the skew. A differential pulse injection oscillator circuit and a pulse injection signal generator circuit are also provided.

A wireless sensor includes an antenna structure, an RF signal circuit, a sensing element, memory and a processing module. In a calibration mode, the sensing element is exposed to a known condition and causes a first change of an operating characteristic of the antenna structure while receiving the RF signal. The processing module generates a first digital value based on the first change and writes it into the memory. In a sense mode, the sensing element is exposed to an unknown condition and causes a second change of an operating characteristic of the antenna structure while receiving the RF signal. The processing module generates a second digital value based on the second change and writes it into the memory.