A passive wireless temperature sensor tag compatible with EPC Gen2 UHF RFID protocol

Abstract

A fully passive wireless sensor tag compatible with electronic product code (EPC) global Class-1 Generation-2 (Gen2) protocol is presented. The whole chip consists of RF/analog front-end, digital baseband processor, multiple-time-programmable (MTP) memory and an on-chip temperature sensor. A clock generator is proposed to meet the low-power requirement of the fully passive operation, with low sensitivity to the process-voltage-temperature (PVT) variations. The temperature sensor is realized by using an energy-efficient successive approximation register (SAR) analog-to-digital converter (ADC) and a low power sub-threshold sensing core, where the sensing core generates a proportional to absolute temperature (PTAT) voltage signal and a reference voltage, and the PTAT signal is digitized by the SAR ADC. A lower power scheme, which is used to generate the backscatter link frequency (BLF), is also proposed to meet the BLF requirement of EPC Gen2 protocol. The whole temperature sensor tag chip is fabricated in the TSMC 0.18 μm CMOS technology and the chip size is 0.62mm . The maximum sensitivity of the tag is -13.1/-11.3 dBm for reading/sensing operation, and the temperature sensing error is -0.55°C/0.79°C over a operating range from -40°C to 85°C. It achieves a reading/sensing distance of over 8/6 m with 4W effective isotropic radiated power (EIRP) by a commercial reader.