This paper introduces a high-efficiency and a wide-frequency band RF-to-DC rectifier with an enhanced voltage conversion ratio (VCR) for implantable biomedical devices. The rectifier utilizes bootstrapped CMOS devices for threshold potential reduction. These devices (NMOS and PMOS) have bootstrapped gates. This is used to reduce the needed RF input voltage which turns rectifying devices ON, effectively adding DC voltages (positive or negative, respectively) to the input RF signal. This allows rectifier devices to conduct at lower input RF voltage levels. The proposed RF-to-DC rectifier circuit is designed and simulated in 180nm CMOS technology. Simulation results show a peak power conversion efficiency (PCE) of 81.3% at RF input power of -12.4dBm, with a load resistor and capacitor of 12 kΩ and 1pF, respectively. With the same loading, the proposed rectifier achieves a peak VCR of 87% at RF peak voltage of 1V. The obtained dynamic range of the proposed circuit is 15.7dB (PCE > 30%) at an input frequency of 402MHz. With an input frequency of 434MHz, the proposed circuit has a PCE of 80.85% at -12.8dBm RF input power, while having a load resistor and capacitor of 12 kΩ and 1pF, respectively. The rectifier achieves 87.14% VCR, and a dynamic range of 15.4dB (PCE>30%).