A 5 GHz, 1.5 V and low power CMOS frequency synthesizer with LC-tuned VCO (voltage controlled oscillator) is presented. The synthesizer consists of an LC-tuned VCO, an injection-lock frequency divider, a very low power prescaler which brings 2.5 GHz range frequency to 11 MHz, a phase-frequency detector and charge-pump with improved architecture. Spiral inductors with Q-factor of 9 are used for the LC-tuned 5 GHz VCO. A fixed 2-frequency divider based on injection-locking phenomenon is used to bring 5 GHz VCO frequency to 2.5 GHz. Both VCO and injection-locked divider's oscillators are tuned with NMOS varactors with their bodies grounded, resulting in about 700 MHz tuning range. Implemented in 0.25μm standard CMOS process, the synthesizer consumes only 13.5 mW with a single 1.5 V supply.