The development of electronic system brings more demands to the accuracy of frequency source

frequency resolution

conversion time and frequency spectrum purity. Phase-locked frequency synthesis technology has small volume

simple circuit and high stray inhibition degree. It has narrow-band filtering capability

so it is used widely. But there is a disadvantage between the frequency step and conversion time constraints. DDS has a very high frequency resolution

extremely fast frequency converting. But its upper limit of output frequency is not high. The two methods have their own advantages and disadvantages. So use DDS + PLL technology solutions which can both retain the advantages of the phase lock loop

and make up for the inadequacy of the phase locked loop. Based on the idea of mixed frequency synthesis method is this paper proposes the improvements.