Synthesized Frequency Sources Research And Implementation

Frequency source is a key component in the modern electronic system and its performances have large powerful effect on the whole electronic system. Currently, the frequency synthesis technique is the main way to achieve frequency sources which are called synthesized frequency sources. With the development of modern electronic technology, the electronic system requires synthesized frequency sources with higher performances, such as lower phase noise, higher spur suppression, and faster frequency switching speed and so on.The theory and implementation of synthesized frequency sources are the main content in this thesis. Firstly, the technical indicators of synthesized frequency sources are described. Secondly, the principle and frequency spectrum characteristics of Direct Digital Frequency Synthesizer (DDS) are discussed. Thirdly, the paper describes the theoretical analysis of Phase Locked Loop (PLL), and explores the basic structure, principle, phase model, phase noise and spurs of PLL synthesized frequency source. Lastly, the DDS-driven PLL frequency synthesis technology has been combined with their merits such as super fine frequency resolution, low phase noise, high frequency accuracy and easy programming for DDS and narrow-band tracing filter and high frequency output for PLL.And DDS&PLL are controlled by Micro-programmed Computer Unit (MCU).So the L-band 1.8GHz-1.9GHz synthesized frequency source with 10MHz frequency step has been designed.Based on the modular concept, the synthesized frequency source has been divided into three independent modules such as DDS module, PLL module and MCU module.DDS module, realized by AD9850 chip, can output signals with frequency range from 18MHz to 19MHz with 100kHz frequency step.The output of DDS is used as the reference input signal of the PLL module.The measurement results of DDS module show that the phase noise of 40MHz synthesized frequency source is about -112dBc/Hz@100kHz and its spurs is about -61dBc in 20MHz frequency range,which fully meet the requirements of the reference input signal of PE3236.The PLL+VCO circuit with output frequency range from 1.8GHz to 1.9GHz is designed with PE3236 PLL chip and MW350-1155 VCO chip.Finally, the content and design experiences are summarized in the last chapter of this thesis.And the tendency and research direction of synthesized frequency source are also introduced at the end of the thesis.