Summary A wirelessly powered temperature sensor is presented in complementary metal‐oxide‐semiconductor (CMOS) 180‐nm process. The wireless power transfer (WPT) is performed using resonant magnetic coupling, and a diode‐less AC to DC conversion is achieved through a quadrature‐oscillator with native‐MOS. The quadrature‐signals are subsequently used to control the diode‐less rectifier switches. The on‐chip temperature sensor exploits the subthreshold region temperature, and the sensed temperature is converted to frequency using a ring‐oscillator, which is implemented using differential cross coupled oscillator‐based delay cells. The temperature sensor architecture also employs a temperature‐insensitive replica circuit to minimize process dependence and enhance power‐supply rejection ratio (PSRR) of the sensing process. The application‐specific integrated circuit has been designed and fabricated in 180‐nm CMOS process and has dimensions of 2 mm × 2 mm. The measurement results demonstrate that the WPT circuit generates a DC voltage of 1V with a power transfer efficiency of 85% for distances 2 to 8 mm with settling time of microseconds to milliseconds. The temperature sensor demonstrates a resolution of < ±0.6C with a sensitivity of 0.52 mV/C and 126.9 Hz/C along with PSRR of −63dB and Integral Non‐Linraity (INL) of 5% measured across six different dies. The back‐scattering communication demonstrates a −53‐dB signal at a distance of 4 mm without affecting the WPT efficiency. The total power consumption of the temperature sensor along with the integrated biases is 120 nW.

An active quasi-circulator (AQC) integrated circuit is designed and fabricated in a 0.18-[Formula: see text]m CMOS process. The proposed design is based on a parallel combination of a common-source (CS) stage and a combined common-drain (CD) and common-gate (CG) topology. Scattering matrix of the core AQC circuit is derived considering MOSFET’s secondary effects, particularly the body effect as well as output loading effects. Measurements of the quasi-circulator reveal an insertion loss of [Formula: see text] dB between transmitter-to-antenna ports ([Formula: see text]) and of [Formula: see text] dB between antenna-to-receiver ports ([Formula: see text]), within a frequency band of 2.2–4.6 GHz. The isolation between the transmitter and the receiver ports ([Formula: see text]) is better than 24 dB with a maximum value of 29.5[Formula: see text]dB @ 3.6[Formula: see text]GHz. The power dissipation of the proposed AQC is 40[Formula: see text]mW and it covers an active chip area of 0.677[Formula: see text]mm2.

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