The Realization Of Charge Pump Phase-locked Loop Frequency Synthesizer

The frequency synthesizer usually plays an important role in communicationsystem, often referred to as the "heart" of system. The performance of the Synthesisdirectly determines the whole system’s index. However, high stability and highaccuracy quartz crystal oscillator is more difficult to design, and is not easy to meet thespecific needs of various occasions towards frequency. Frequency synthesis technologyhas solved the above problem very well. It not only produces a series of frequencyaccording to the demand, but also reaches the level of reference oscillator on accuracyand stability.This paper adopts phase locked loop frequency synthesis technology to design anonline programmable low noise frequency synthesizer, according to the design index.As we know, when we want to change the output frequency of the traditionalfrequency synthesizer, usually we need to detach the phase-locked loop from thesystem, and change the control word through the burn tool, in order to change itsoutput frequency. This method is tedious in the actual operation, low efficiency, withone time only one output frequency. So, this paper proposes a more simple method,namely, online programming, by altering the control word online, which can changesynthesizer output in real time, improving efficiency greatly. On the other hand, inorder to reduce the system ’s phase noise and spur as far as possible, we used a seriesof methods, such as choosing a new type of charge pump PLL, improving charge pumpcurrent, using high order loop filter, reducing the loop bandwidth, and so on.First of all, we carry on some simple introduction on frequency synthesistechnology, and analysis of the technology of frequency synthesis performance index.Then, we introduce the theory of PLL frequency synthesizer technology, with emphasison the charge pump phase locked loop. Next, we discuss the PLL phase noise andreference spur, in order to find the effective ways to reduce noise. After that, we givethe overall system architecture and select the chip. This paper chooses the three orderpassive loop filter, which has good inhibition of spurious performance, whose parameters can be calculated by using the MALTAB. Finally, complete the PCB designof the system, do the experiment, and analyze the experimental results.