The operating principle of MOS FETs AC/DC rectifier for passive RFID transponder is introduced and the power dissipation of MOS rectifier operating with 902M-928MHz industrial, scientific, and medical (ISM) carrier frequency is presented in details in this paper. In order to maximize the operating range of RFID transponder, low power design techniques are needed. Therefore, the key design parameters optimization of passive rectifier is discussed in this paper. Besides, the paper also discusses some design tradeoffs between area, power efficiency, communication bandwidth, the stability of output DC supply voltage