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

A 5GHz, 1.5 Volt 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 2.5GHz range frequency to I I MHz, a phase-frequency detector and charge-pump with improved architecture. Spiral inductors with Q-factor of 9 are used for the LC-tuned 5GHz VCO. A fixed 2 frequency divider based on injection-locking phenomenon is used to bring 5GHz VCO frequency to 2.5GHz. Both VCO and injection-locked divider's oscillators are tuned with NMOS varactors with their bodies are grounded, resulting in about 700MHz tuning range. Implemented in 0.25u standard CMOS process, the synthesizer consumes only 13.5mW with a single 1.5V supply.