A RF powering circuit used in Radio Frequency IDentification (RFID) tags and other battery-less embedded devices is presented in this paper. The RF powering circuit harvests energy from electromagnetic waves and converts the RF energy to a stable voltage source. Analysis of a NMOS gate-cross connected bridge rectifier is conducted to demonstrate relationship between device sizes and Power Conversion Efficiency (PCE) of the rectifier. A rectifier with 38.54% PCE under normal working conditions is designed.