A 5 GHz, 1.5 V and very low-power CMOS frequency synthesizer for wireless communications

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.