A Wideband Frequency Source Research

The requirements for signal source improve as the development of radiotechnology,which involve stabilization， accuracy of frequency response andconvenience for using. Common quart crystal oscillator is not flexible of frequencyconversion though with good stabilization，accuracy of frequency response. While LCoscillator is being phased out gradually because its FM output range is smaller andfrequency response is less stable and accurate. In order to meet the requirement ofstabilization， accuracy of frequency response and convenience for using, mixedfrequency synthesizer has been developed much to find good applications.The thesis introduces the based theory and the functions of Mixed frequencysynthesizer, and analyzes the production and inhibition method of the two key indexesof Frequency synthesizer (phase noise, spurious). The noise produced by fractionalfrequency division is eliminated with the Σ-Δmodulation technique to obtain the signalsource with flexible frequency conversion,high resolution and high stability.The thesishas presented the designs, calculations, simulations, and experiments of0.5~2.6GHzfrequency source and550MHz,1150MHz Frequency point source.The widebandfrequency source use PLL to provide reference for the ADC, and the DDS excite thePLL circuit structure directly,which is able to balance the advantages and disadvantagesof DDS and PLL circuit to achieve a better overall technical indicators. Theexperimental results show that frequency source can achieve a frequency range of500MHz-2600MHz with step1MHz,stray better than55dBc（Seventy percent of thefrequency range）and Phase noise better than-90dBc/Hz@1kHz.Modular design is applied in the hardware design. The circuit is divided intoPLL1、DDS、PLL2and MSP430as control center by the functions. which simplifies thecircuit design and reduces the difficulty of debugging. It’s shown in the experiments thatthe performance of signal source is better than the requirements of the system.The thesis involves the optimization of DDS spurious suppression，PLL phasenoise, the analysis of the advantages and disadvantages of the various combinations of DDS and PLL and the design and manufacturing of the system platform (PCB, cavity,etc.).Σ-Δmodulation technique is used to eliminate the noise produced by fractionalfrequency division to obtain a significant effect,which has a certain reference value tofurther exploration of frequency synthesis technique.