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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 2. The structure of the new second order PLL
Extracts from the Article
针对传统锁相环路跟踪速度与跟踪精度之前的矛盾,本文借鉴非线性控制思想,在传统锁相环路中耦合非线性元件,利用非线性元件的控制作用自适应调节环路滤波器的输出,平衡环路的跟踪速度与跟踪精度之间的矛盾。新型环路结构如图2所示。
由图2可以看出,新型环路中在环路滤波器之后利用非线性元件N和一个低通滤波器控制压控振荡器的输出,其中非线性元件N的数学表达式如式(6)所示
耦合非线性元件实际上是根据环路输入输出相位误差自适应调节环路噪声带宽:当相位误差较大时,利用较大的环路带宽迅速减小相位误差;当相位误差由于环路控制作用而减小时,利用较小的带宽抑制噪声,从而实现精确跟踪的同时提高跟踪速度。根据图2,建立起这种新型二阶锁相环路状态方程如式(7)~式(12)所示。
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