A low power CMOS temperature-to-frequency converter for RFID applications

This paper presents the design of a low power temperature sensor based on temperature-to-frequency conversion for RFID applications. The variation of temperature is detected by a PTC resistor that determines the reference current of a bootstrapped cascode source. This current is used to bias an active inductor. The self-resonance frequency varies accordingly to the shift of the current, thus providing the temperature to frequency conversion. The circuit has been implemented using a standard 65 nm CMOS technology. A frequency of oscillation of 31.3 MHz at 20°C has been obtained, with an estimated sensitivity of 50.5 kHz/°C, a resolution of 0.12°C and a power consumption of 21.8 uW within the 0–80°C temperature range.