Abstract: A band III PLL Frequency Synthesizer is integrated in a 0.18μm 1.8V CMOS process,except for the tuned inductor and loop filter.Some functions such as selecting the sub-band of the VCO,configuring the currents of the charge pump and VCO etc,can be performed by using the SPI bus.An improved band-switching circuit is adopted to save band-switching time.As the measurement results show,the total power of the frequency synthesizer is 34mW;the frequency range of frequency synthesizer’s output is 143~271Mhz.The phase noise in band III can reach -83dBc/Hz@10kHz,-104dBc/Hz@100kHz and the reference spur is less than -70dBc.This new band-switching circuit can save band-switching time in comparison with the normal one.

Key words: frequency synthesizer, PLL, switched-capacitor array, VCO, band-switching circuit