Comparative study on time-to-digital converters for low-power RFID tag sensors

This paper presents a comparative study on time-to-digital converters (TDC) for their use as part of an RFID tag sensor. TDCs can digitize any physical magnitude previously converted to time delay and exploit the benefits of time domain conversion: high resolution with reduced power consumption and low voltage operation. Three different TDC architectures are analyzed and a calibration strategy tailored for RFID sensing applications is proposed in order to account for process variations. Converters implemented using a 0.18μm CMOS standard process have been analyzed at transistor level for human body temperature sensing applications. An accuracy of 0.011 °C is achieved in the range from 35 °C to 43 °C for the nonius TDC with a power consumption of only 4.1 nW at 10 samples per second from a 1.8 V voltage supply.