An ultra-wideband ultra-low phase noise frequency synthesizer

In order to solve the problems of frequency band expansion in direct frequency synthesis method and serious additional deterioration of phase noise in phase-locked frequency synthesis method, a mixer phase-locked frequency synthesizer combining direct analog frequency synthesis and phase-locked frequency synthesis is designed. In order to reduce the frequency multiplication times of the phase detector and optimize the phase noise of the output signal, the frequency synthesizer uses a comb spectrum generator to excite an offset signal with ultra-low phase noise for mixing. In the meantime, the error-lock problem is solved in ultra-wideband mixing phase-locked loop (PLL). An ultra-wideband frequency synthesizer with frequency band 12 GHz–24 GHz and step of 100 MHz is designed in this paper. The experimental test of the frequency synthesizer shows that the phase noise of the frequency synthesizer is better than -116 dBc/Hz@1 kHz at low frequency 12 GHz, and −109 dBc/Hz@1 kHz at high frequency 24 GHz. This phase noise is basically the same as the direct analog frequency synthesis method and is 20 dB better than the conventional phase-locked scheme. The frequency synthesis method has the advantages of ultra-wideband and ultra-low phase noise, and it can be used in the high performance electronic equipment.