Fast automatic frequency calibration for wide-band CMOS frequency synthesizer

Abstract

This thesis describes a 2∼6GHz CMOS frequency synthesizer with only one LC-tank voltage controlled oscillator (VCO) and a fast automatic frequency calibration (AFC) technique. The LC-tank VCO oscillating at 6∼8GHz provides the required LO frequency by dividing and mixing the VCO output clocks appropriately. The frequency of the VCO is coarsely tuned by an automatic frequency calibration circuit. The proposed AFC scheme provides fast calibration time by updating the frequency control code right after the frequency error is detected. Two-phase reference clocks are employed while eliminating the uncertainty of the initial phase relationship between the reference clock and VCO output, resulting in decreased AFC time. The frequency synthesizer is based on a fractional-N phase locked loop (PLL) employing a third-order 1-1-1 MASH type sigma-delta modulator. The frequency synthesizer is implemented in a 0.18 m CMOS process and occupies 0.92mm2 while the AFC occupies only 0.01mm2. The AFC operation is completed less than 1.6 s. Power consumption is less than 36mW from 1.8V supply voltage. Experimental results show that the phase noise is -110.5dBc/Hz at 1MHz offset from the carrier.