Broadband Tunable Low Phase Noise Frequency Synthesizer Design And Implementation

With the rapid development of science and technology, frequency synthesizer has been widely used in fields of electro-communication, such as radio astronomy, satellite navigation,3G communication, electronic warfare and radar surveying. Frequency synthesizers of high quality are indispensable parts in these advanced systems because their performance to a large extent influences the performance of electronic systems. That how to design a frequency synthesizer of broad frequency bandwidth, high-resolution, low phase noise, low cost and high stability has become a hot research topic in these days.Frequence resolution is one of the important specifications of the frequency synthesizer. This dissertation introduces DDS technology and fractional-N technology to achieve the lHz resolution required for frequency synthesizer design and chooses the latter technology for its appropriateness in the frequency synthesizer realization of large frequency span in this research. Then it introduces relevant theories of fractional-N technology and its wideband FM technology realization methods, proposes the overall design of frequency synthesizer of low phase noise and adjustable broadband FM.The design of synthesizer was divided to the design of fractional-N synthesizer and the design of broadband FM. And hardware and software designs of the frequency synthesizer are given based on the design. The hardware design includes phase-locked loop circuit design and the FM circuit design. While introducing the phase-locked loop circuit design, equipment of PFD, charge pump, variable loop filter, divider circuit and out of lock detection circuit design are also given detailed descriptions. While introducing the FM circuit design, equipment of in-band frequency modulation and out-of-band frequency modulation are given detailed description as well. Software design is illustrated in detail with fractional divider, Σ-△modulation, DAC gain compensation and in-band modulation. The final test result of the designed frequency synthesizer reveals that all its specifications meet the design requirements.The frequency synthesizer designed in this research is of broadband FM function and of excellent specifications, which are Frequency range of500MHz-1000MHz, the output power of+10dBm, the phase noise better than-105dBc/Hz@20kHz, the frequency resolution of lHz, the frequency modulation rate of DC-100kHz, maximum modulation frequency deviation of5MHz. However, the above specifications are restricted by the VCO chosen in this dissertation, thus this research is just to verify the implementation feasibility of broadband FM program; if for better specifications, the program can be successfully applied to the specific frequency synthesizer design according to relevant demands.