A circuit device includes an oscillation circuit and a processing circuit. The oscillation circuit includes a variable capacitance circuit configured by a capacitor array and oscillates at an oscillation frequency corresponding to the capacitance value of the variable capacitance circuit. First temperature data and second temperature data subsequent to the first temperature data are input to the processing circuit as temperature data. In the period between the start of the capacitance control based on the first temperature data and the start of the capacitance control based on the second temperature data, the processing circuit switches the first capacitance control data corresponding to the first temperature data and the second capacitance control data different from the first capacitance control data in a time-division manner to be output to the variable capacitance circuit.

Embodiments of oscillator circuits for wireless transmission of data are disclosed herein. In one example, an oscillator circuit includes an active network and a passive differential network coupled to the active network is disclosed. The active network is configured to generate an active signal for sustaining oscillation of the oscillator circuit. The passive network includes a first subnetwork, a second subnetwork, a first inductor and a second inductor. The first subnetwork is configured to adjust a central value of a resonant frequency of the oscillation. The passive network further includes a second subnetwork configured to further adjust the resonant frequency of the oscillation.

A radio frequency identification (RFID) tag includes an antenna structure operable to receive a radio frequency (RF) signal, an RF signal circuit operable to, when enabled, produce the RF signal, a sensing element operably coupled to the antenna structure, a memory, and a processing module. When in a calibration mode, the processing module adjusts the input impedance until a measured power level is substantially equal to the desired input power level, and generates a first digital value based on the amount of the adjustment a power difference between a measured first input power level and a desired power level, and stores the first digital value in the memory, where the first digital value is representative of a known condition. In a sense mode, the processing module adjusts the input impedance until a second measured power level is substantially equal to the desired input power level, and generates a second digital value based on the amount of the adjustment a power difference between a measured first input power level and a desired power level, and the desired power level, and stores the second digital value in the memory, where the second digital value is representative of an unknown condition.

Disclosed is an authentication reader intended to be installed on a motor vehicle opening element, the reader including a microcontroller, at least one transmitter, at least one matching circuit and a single antenna, called primary antenna, characterized by a working frequency. The matching circuit includes switching element able to switch the matching circuit between a first mode, in which the matching circuit makes it possible to match the primary antenna to a secondary antenna of an authentication device whose resonant frequency is lower than the working frequency, and a second mode, in which the matching circuit makes it possible to match the primary antenna to a secondary antenna of an authentication device whose resonant frequency is higher than the working frequency.

A communication system includes a passive wireless sensor and a sensor computing device. The passive wireless sensor is operable to receive a radio frequency (RF) signal including a carrier frequency signal and a modulated sense request signal, generate a power supply voltage, determine received signal strength (RSSI) of the RF signal, and determine whether the RSSI is at a desired level. When the RSSI is at a desired level, the passive wireless sensor generates a response RF signal including the carrier frequency and a coded sense response signal representative of a sensed environmental condition. The sensed environmental condition affects impedance of a front-end of the passive wireless sensor to produce an affected impedance. The passive wireless sensor generates the coded sense response signal based on tuning the affected impedance to resonate with the carrier frequency signal. The computing device operable to: transmit the RF signal, receive the response RF signal, and generate an environmental condition value based on the coded sense response signal and environmental conversion information.

A radio frequency identification (RFID) tag includes an antenna operable to receive a radio frequency (RF) signal having a carrier frequency. The RFID tag further includes a tank circuit coupled to the antenna. The RFID tag further includes a tuning circuit operable to determine a received power level of the RF signal at the carrier frequency, determine whether the received power level is lower than a power level threshold. When the received power level is lower than the power level threshold: tuning circuit increases the input impedance of the RFID tag, determines a most recent power level of the received RF signal, and compares the most recent power level with the received power level. When the most recent power level is greater than the received power level, the tuning circuit incrementally increases the input impedance until the received power level is substantially equal to the power level threshold.

A method includes transmitting, by a radio frequency identification (RFID) reader, a series of RF signals to RFID tags in a time sequence. A first RF signal includes a first message for responding when received signal strength corresponds to a first power level and a second RF signal includes a second message for responding when the received signal strength of the RF signal corresponds to a second power level. The method further includes receiving, by the RFID reader, a first set of responses from a first set of RFID tags that received the first and second RF signals at a received signal strength corresponding to the first power level. The method further includes receiving, by the RFID reader, a second set of responses from a second set of RFID tags that received the first and second RF signals at a received signal strength corresponding to the second power level.

Techniques are described for tuning a resonant circuit using differential switchable capacitors. For example, embodiments can operate in context of a power amplifier with a tunable resonant output network. To tune the network, multiple differential switchable capacitors are provided in parallel. Each differential switchable capacitor can include a pair of capacitors, each coupled between a respective internal node and a respective differential terminal; and the internal nodes are selectively coupled or decoupled using a respective electronic switch (e.g., transistor). Switching on one of the differential switchable capacitors forms a capacitive channel having an associated capacitance. Each differential switchable capacitor can also include a switch network to selectively pull the internal nodes to a high or low voltage reference according to the selected operating mode.

A radio frequency identification (RFID) tag includes an antenna structure operable to receive a radio frequency (RF) signal, an RF signal circuit operable to, when enabled, produce the RF signal, a sensing element operably coupled to the antenna structure, a memory, and a processing module. When in a calibration mode, the processing module adjusts the input impedance until a measured power level is substantially equal to the desired input power level, and generates a first digital value based on the amount of the adjustment a power difference between a measured first input power level and a desired power level, and stores the first digital value in the memory, where the first digital value is representative of a known condition. In a sense mode, the processing module adjusts the input impedance until a second measured power level is substantially equal to the desired input power level, and generates a second digital value based on the amount of the adjustment a power difference between a measured first input power level and a desired power level, and the desired power level, and stores the second digital value in the memory, where the second digital value is representative of an unknown condition.

A circuit for calibrating an injection locked oscillator is provided. The injection locked oscillator includes an injection locking input, an LC tank and an oscillator output to output an oscillator output signal. The circuit is configured to adjust a capacitance of the LC tank to different values, detect an amplitude of the oscillator output signal for each value of the different values of the capacitance while an input signal having a target frequency is applied to the injection locking input, determine a maximum amplitude of the detected amplitudes, and select a value for operating the injection locked oscillator based on the determined maximum amplitude.