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A Novel Second Order Phase Locked Loop with Adaptive Adjusted Bandwidth
ZHAO Lei,SHI Lei,ZHU Congying,YAO Bo
Electronic Science and Technology    2019, 32 (1): 1-4.   DOI: 10.16180/j.cnki.issn1007-7820.2019.01.001
Abstract   (391 HTML19 PDF(pc) (1392KB)(52)  

The large acquisition bandwidth presents a significant challenge to traditional second-order phase locked loops. On the basis of the contradiction of larger acquisition bandwidth and noise reduction capabilities, a novel second-order PLL which was coupled with a nonlinear element, was introduced in this paper. The loop noise bandwidth was adaptively adjusted by the nonlinear element. The frequency error was reduced more quickly with a larger bandwidth when the frequency error was large. By contrast, the noise was suppressed with a smaller bandwidth to improve the tracking accuracy when the frequency error was reduced due to the control effect of the loop. The simulation results indicated that the tracking speed of the proposed nonlinear second order PLL was significantly increased and the acquisition bandwidth was increased from 4 kHz to 18.8 kHz.


Figure 3. Non-linear element N
Extracts from the Article
其中,y*是非线性元件的拐点,mlmh表示两段斜率。环路初始工作时,输入输出相位误差较大,压控振荡器的控制电压也较大,此时利用mh的放大作用,快速调整压控振荡器的振荡频率,缩小输入输出相位误差。当环路工作一段时间后,由于环路的控制作用,输入输出相位误差减小,此时利用ml的压缩作用,抑制控制电压中的残留噪声,实现环路的精确跟踪。这三个待选参数与环路性能的关系可总结如下:当y*较小,mh较大时,环路具有较高的跟踪速度;当y*较大,ml较小时,则环路抑制噪声的能力较强。式(6)中非线性元件N的图形表示如图3所示。
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