4.2W CMOS Frequency Synthesizer for 2.4GHz ZigBee Application with Fast Settling Time Performance

A new frequency synthesizer with low-power and short settling time is introduced. With two-point channel controls for an integer-N PLL, we have achieved a near zero settling time for any frequency change in 2.4GHz ZigBee band. By utilizing a vertical-NPN parasitic transitor for the VCO biasing, the close-in phase noise has been improved by 5dB from the case of MOS biasing. A modified-TSPC topology is proposed for low-voltage frequency divider circuits. Using the 1.2V supply voltage for 0.18μm CMOS, the power consumption is only 4.2mW and the phase noise is-116.5dBc/Hz at 1MHz offset.