Research Of X Band Frequency Synthesizer

Frequency synthesizer is the hardcore of modern communication systems. With the incredible development of science, the requirement of frequency synthesizer is much higher, from single frequency to multi-frequency, from low frequency resolution to high frequency resolution as well as the lower phase-noise and spur.A single-PLL broad-band small-step frequency synthesizer is represented in this paper, which is derived from the need of our project. This synthesizer has a simple structure, and it takes up only a few I/O sources. Including the phase detector ADF41020, the active loop filter and the broad-band VCO, it is working at the frequency range of 8~8.3GHz in X band and 6~8GHz in C band with 10 MHz steps. Its performance, whose phase noise is better than-85dBc@100k Hz and spur is lower than-60 dBc, is also measured. This thesis is mainly focus on the below two parts:1. The characteristics of loop filter, and its effects to the phase noise, spurious suppression and locked time, and the design method of loop filter in wide band application.2. The selection of the synthesizer components, the design and the implementation of synthesizer circuits.In the article structure, firstly, the fundamental principle and specifications of phaselocked loop are introduced in this thesis. Secondly, some structures of loop filter are analyzed and the features of broad-band loop filter are discussed base on frequency response simulations. Thirdly, the system solution is established by comparison, and its implementation is described from the aspects of component selection, the design of power supply, power divider, loop filter as well as schematic and PCB layout. In addition, some experience on debugging are shared and several typical cases are represented. Finally, the test results of this frequency synthesizer measured by spectrum analyzer, including frequency specification, phase noise, spur suppression and locked time, are provided, which verifies the validity of this broad-band single phase-locked loop solution.