窄带Dither算法在流水线ADC中的研究与应用设计

【作者】 张云；

【导师】 李广军；

【作者基本信息】 电子科技大学 ， 通信与信息系统， 2011， 硕士

【摘要】 流水线结构的模数转换器(Pipelined ADC)具有高分辨率、高精度的特点以及良好的速度与功耗性能,其结构在面积和功耗上具有很大的优势。然而,由于电路中存在各种非理想因素,极大地限制了流水线ADC性能的提高。对于提高ADC的SFDR(无杂散动态范围)特性,引入Dither噪声是一种重要的方法。Dither能够有效地改善因量化过程、相干采样和ADC的非线性特性而造成的谐波失真,从而提高ADC的无杂散动态范围。因此,将Dither噪声和当前主流的流水线ADC结构相结合,对于设计下一代高性能ADC具有重要的作用。本文首先分析从理论上分析了ADC的量化过程、相干采样和非线性特性所引起的谐波失真和Dither对ADC动态性能的改善,并对改善的原理进行了说明。然后,从数学上推导了Dither通过影响ADC的输出码密度函数来改善DNL所引起的总误差,推导了高斯分布的Dither对理想ADC的量化误差的改善。接着,本文在分析流水线ADC结构的基础上,搭建了一个14位的流水线ADC行为级模型,并构建窄带Dither的仿真系统,对窄带Dither对流水线ADC无杂散动态范围指标的改善情况进行了仿真分析,并提出了一种与传统窄带Dither产生方式略有不同的新型窄带Dither,这种新的窄带Dither可以避免频率由设计的模拟滤波器所限制,要改变Dither信号的频率只能重新设计新的Dither发生电路的局限性。针对引入Dither后发生信号溢出的情况,本文进行了一些探讨,提出了两种解决方案,并进行了仿真验证,证明所提出的方案能够有效的解决引入Dither后信号溢出的问题。最后,通过设计PCB电路板,以12位的ADC(AD9235)为目标实测了窄带Dither对ADC性能的影响,证明了窄带Dither对ADC的SFDR性能的改善。更多还原

【Abstract】 Pipelined ADCs are characteristic of high resolving power, high precision and have good characteristic of rate and consumement. But nonideal factors in circuit restrict the enhancement of performance of pipelined ADC. Dither technolgoy is a important means to enhancement of SFDR ( Spurious Free Dynamic Range ) performance of pipelined ADC.Dither technology is possible to reduce the harmonic distortion caused by quantization, coherent and nonlinearities of ADC to improve Spurious Free Dynamic Range. Therefore, combining the dither technolgoy and pipelined ADC is a important process to design next generation high performance ADC.First of all, this paper analysis theoretically the the harmonic distortion caused by quantization, coherent and nonlinearities of ADC and dither’s influence on ADC’s dynamic performance, and explain the principle of improvement.Afterward, by mathematic manner, explain the dither improve ADC’s total error result from DNL (Differential Nonlinearity Error) by affecting the probability of code occurrence and reduce the quantization Errors of ideal ADC.Next, this paper design behaviro model of a 14 bits pipelined ADC via analysing the structure of pipelined ADC and emulate the improvement of pipelined ADC’s SFDR performance after adding the narrow-band dither into the input signal. After that, introduce a new narrow-band dither which is brought by different manner from conventional narrow-band dither. The new narrow-band dither can avoid its frequency restricted by a Analogue filter which require a new design when the frequency of dither is changed.For the problem that the signal may overflow the maximum of ADC after adding dither, this paper advance two blue print and prove its correctness by emulation mode.In the end, prove that narrow-band dither can improve ADC’s SFDR performance by designing Printed Circuit Board whose objective is AD9235 and test the improvement of ADC after adding dither into the input signal.更多还原