C-band Frequency Synthesizer

Frequency synthesizer is the key circuit of modern communications systems, is the main source of electronic systems. Frequency synthesizers are widely used in digital communications, satellite communications, radar, navigation, and other fields. Countries around the world attach great importance to study the frequency synthesizer, wide frequency band, high frequency stability, low phase noise, low spurious, small step and fast frequency switching speed frequency synthesizer is the main trends of contemporary development. Studying C-band frequency synthesizer has great significance in the area of satellite communications, digital televisions, medical equipments and so on. Based on this background, this subject is to design a C-band frequency synthesizer which has low phase noise, low spurious and high-stability. And this synthesizer is to provide local oscillators for a front-end transceiver.At first, this paper introduces the history of the frequency synthesizer, recent development around the world, and then analyzes the principles of Phase-Locked Loop, phase noise and combinations of traditional PLL. After compared their advantages and disadvantages, decided to use double phase locked loop mixing technology to achieve this C-band synthesizer. Finally, describes the design methods, working principles, debugging processes and test results of this subjectThis topic comes from an engineering project. It requires two local oscillators for its transceiver. The first one should provide a frequency point of 1112.5MHz, the second should provide frequency range of 4.7 ~ 5.5GHz. According to system's target, the first local oscillator uses single PLL to output the frequency 1112.5MHz directly. The second one uses double loop-mixing technology, through frequencies choosing, making sure that the frequency synthesizer not only can ensure low spurious but also improve the phase noise level. This paper focuses on the design process of two local oscillators, including device selection, design of EMC and problems and solutions of debugging process. The final test shows the phase noise performance, curves of spurious. From the test results we can see, the two local oscillators meet the system targets. The second LO with 4.7 ~ 5.5GHz frequency output has 0.5MHz step spacing, spurious suppression better than 65dBc, at 10KHz phase noise is better than -86dBc/Hz.