A new differential drive CMOS rectifier topology has been provided for RF wireless energy harvesting of low input power applications as implantable devices. It applies a dynamic threshold compensation technique by gate biasing of selected MOS switches with external bootstrapping circuit. The proposed architecture has been simulated in 0.18μm CMOS technology. The performance of the circuit is evaluated in terms of the power conversion efficiency (PCE), and the voltage conversion ratio (VCR). The proposed architecture has achieved a maximum power conversion efficiency of 75% and a voltage conversion ratio of 83.9% at 402MHz and -15.4dBm RF input power. The DC output power exceeds 21μW with a parallel combination of 10kOhm and 2pF load. The design layout has 0.085mm2 chip area.