Aiming at the requirements of low power consumption of RFID sensor tag

design a CMOS temperature sensor based on ring oscillator. The proposed temperature sensor first generate a PTAT current

and then generate a PTAT frequency by a ring oscillator. A counter counts this frequency to achieve the conversion of frequency to digital code. The measurement results show that the proposed temperature sensor only consumes 125 nW and the temperature error is sensor only-0. 7/1. 2 ℃ within the range of-40

80 ℃

which is especially suitable for RFID application.