A Millimetre Size Wireless Temperature Sensor with Digital Conversion and Embedded 2.5 GHz Transmitter and Antenna

摘要

The on-chip antenna concept is the actual trend in integrated wireless sensor systems because it is a practical solution to compact, small size and low cost devices for short range wireless applications, like RFID tags and biomedical sensor data transmitters and other related applications. Due to the typical small chip dimension, only high frequency bands can use these antennas in optimum, i.e., resonating, conditions. Although the chip dimension do not allow resonant radiating elements, nevertheless this does not seem to be a limit for the specific application in contactless sensing, where a short distance wireless link is sufficient. In this paper an improvement of a wireless temperature sensor with on-chip antenna is presented. This solution, realized in 0.35 urn CMOS technology, exploits a proportional to absolute temperature (PTAT) voltage scheme, where the difference between two base-emitter voltages under different bias current densities is constantly measured. The availability of bipolar transistors in CMOS technology allows to exploit their properties in temperature sensor applications. The signal is transmitted by a small loop antenna structure which is realized by aluminium deposition on the top surface of the chip.