ABSTRACT
This chapter provides a graphical view of the transponder-to-reader link using both direct transmission and backscattering. Passive wireless microsystems such as radio-frequency-identification (RFID) tags, smart dusts, and temperature sensors for environmental monitoring are usually fabricated using low-cost complementary metal-oxide-semiconductor (CMOS) technologies. Based on how the timing reference is recovered from the signal transmitted by the reader, the mechanisms for remote frequency calibration of passive wireless microsystems can be loosely categorized into the following two groups: carrier-based frequency calibration and envelope-based frequency calibration. The unmodulated carrier sent by a reader to a transponder provides the operation power of the transponder. This signal can also be used as a timing reference to calibrate the frequency of the local oscillator of the transponder. When two oscillators with different but close frequencies are weakly coupled, they synchronize each other such that in the steady state they both oscillate at the same frequency. This phenomenon is known as injection locking.
