An adaptive frequency synthesizer architecture reducing reference sidebands

An adaptive phase-locked loop (PLL) frequency synthesizer architecture for reducing reference sidebands at the output of the frequency synthesizer is described. The architecture combines two tuning loops: one is the main loop for locking the PLL frequency synthesizer and operating all the time, the other one is auxiliary loop for reducing reference sidebands and operating only when the main loop is closely locked. A 1.8V 1GHz fully integrated CMOS dual-loop frequency synthesizer is designed in a 0.18um CMOS process. The suppression of the reference sidebands of the proposed frequency synthesizer is 13.8dB more than that of the general frequency synthesizer.