A Fully Passive RFID Temperature Sensor SoC With An Accuracy Of ±0.4C (3σ) From 0°C To 125°C

This paper presents a fully passive 13.56 MHz RFID temperature sensor system-on-chip. Its power management unit (PMU) operates over a large temperature range using a zero temperature coefficient (TC) bias source. On-chip temperature sensing is accomplished with low voltage, low power CMOS circuitry and time-domain signal processing. Two operating modes have been defined to study supply noise sensitivity: command mode and listening mode, which represent sensor operation during RFID command transfer and listening, respectively. Besides a standard readout command, a customized serial readout command is utilized to distinguish the data from both modes. In command mode, the sensor suffers from interference from the RFID command packet and outputs interference as well, while the sensor outputs no interference in listening mode. Measurements show that sensor resolution in listening mode is improved by a factor of approximately 16 compared to command mode. The chip was fabricated in a standard 0.35 mu m CMOS technology and chip-on-board mounted to a tuned RFID transponder coil on an aluminum core FR4 PCB substrate. Real-time wireless temperature sensing has been demonstrated with a commercial HF RFID reader. With a two-point calibration, the SoC achieves a 3 sigma sensing accuracy of +/- 0.4 degrees C from 0 degrees C to 125 degrees C.