CMOS fully-integrated wireless temperature sensors with on-chip antenna

An improvement of this design involves the implementation of a technique, based on a mathematical procedure between two different signals, that allows the extraction of reliable information on temperature, regardless of the bias voltage variation, and without recurring to power consuming voltage regulators. This concept is implemented, on the same chip, by using two 3-stage ring oscillators with slightly different frequency-vs-temperature characteristics, both close however to 2.4 GHz, switched alternatively on for a few milliseconds. Each ring-oscillator has its own antenna and the device is realized with a standard 0.35 μm process. The higher frequency highly improves the antenna efficiency, which have now a three-fold larger area with respect to the previous case.