This thesis deals with radio frequency power harvest and remote calibration of system clock of passive wireless microsystems. The proposed method of RF power harvesting utilizes a step-up transformer inserted between the antenna and voltage multiplier of passive wireless microsystems to perform both impedance transformation for power matching and voltage amplification prior to rectification. The series resistance of the primary winding is minimized while in the secondary winding, the shunt capacitive losses are minimized. The detailed analysis of the proposed method and simulation results from Spectre of Cadence Design Systems are presented. The proposed power-matching and gain -boosting network, together with voltage multipliers, has been implemented in TSMC-0.18..m 1.8V6-meatl CMOS technology with thick metal options. For the purpose of comparison, a LC power-matching and gain-boosting network with the identical voltage multiplier has also been implemented on the same chip. Measurement results demonstrate that the proposed transformer power-matching and gain-boosting technique greatly improves the power sensitivity and efficiency as compared with widely used LC matching approaches.The proposed calibration method adjusts the frequency of the local oscillator of passive UHF wireless transponders to the desired values using an injection-locked phase-locked loop (IL-PLL). A new relaxation oscillator whose oscillation frequency is less sensitive to supply voltage fluctuation is also proposed. The power consumption of the proposed IL-PLL is minimized by operating it the sub-threshold. A detailed analysis of non-harmonic injection locking of relaxation oscillators including locking and pulling dynamics is presented. A new integrating feedback is proposed to increase the lock range and hold the locked frequency in the absence of the injection signal. The proposed ILL-PLL has been fabricated in TSMC-0.18.