随机量化驱动的DAC谐波抑制与弱信号生成
Harmonic Suppression and Weak Signal Generation Method for DAC with Stochastic Quantization
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摘要: 雷达半实物仿真中,目标回波仿真至关重要。由于目标距离变化、雷达天线主旁瓣比等因素,回波功率动态范围极大,与此同时,现代雷达通过硬件设计和信号处理,也获得了大动态范围回波处理的能力,使得半实物雷达回波模拟系统必须具备大动态范围回波信号生成能力。当前回波模拟信号功率的控制主要通过数字衰减和模拟衰减两个部分完成。数字衰减通过数字信号幅度实现,受限于数模转换器(Digital-to-Analog Converter, DAC)的量化位数和信号质量;而模拟衰减则通过数控射频衰减器实现,受制于信号隔离度限制,导致实现大动态范围功率控制需要付出较高的硬件成本与设计复杂度的双重代价。本文主要关注数字衰减动态范围扩展。DAC量化产生的噪声谐波是制约数字衰减的主要因素,现有消除量化噪声谐波的主要方法是添加抖动,通过在量化前引入抖动信号,破坏量化噪声与输入信号的相干性,从而抑制谐波分量的产生。本文提出随机量化模型,将量化过程抽象为从实数到整数的随机映射过程,证明了传统量化抖动方法是随机量化的一个子集,并推导出最优随机量化方案。基于此,本研究设计了结合模拟衰减与数字衰减的回波信号功率控制策略,在有限模拟衰减的约束条件下,通过集成随机量化技术,成功实现了信号功率的大动态范围控制及微弱信号生成能力。Abstract: Echo simulation is crucial in radar hardware-in-the-loop simulations. The dynamic range of echo power is extremely large owing to factors such as target distance variation and the radar antenna main-to-side lobe ratio. Modern radars can process echoes with wide dynamic ranges through their hardware design and signal processing, requiring the radar echo simulation system to possess the ability to generate echoes with large dynamic ranges. At present, the control of echo simulation signal power is primarily accomplished through two components: digital attenuation and analog attenuation. Digital attenuation is achieved by adjusting the amplitude of the digital signals and constrained by the quantization bits and signal quality of the digital-to-analog converter (DAC). In contrast, analog attenuation is implemented via digitally controlled radio-frequency attenuators, and limited by signal isolation requirements, resulting in higher hardware costs and increased design complexity to achieve large dynamic range power control. This study focuses on the dynamic range extension of digital attenuation. Quantization-induced noise harmonics in DACs constitute the predominant bottleneck restricting digital attenuation. The prevailing approach for mitigating such harmonics involves dithering techniques, in which an intentionally introduced dithering signal prior to quantization disrupts the coherence between the quantization noise and input signals, thereby suppressing harmonic generation. This study proposes a stochastic quantization model that formalizes the quantization process as a stochastic mapping from real numbers to integers. We theoretically prove that conventional dither-based quantization represents a subset of stochastic quantization and derive an optimal stochastic quantization scheme. Building on this framework, we develop a novel echo power control strategy that synergistically integrates analog and digital attenuation. Under the operational constraints of limited analog attenuation, the proposed scheme achieves wide-dynamic-range signal power control and weak signal generation through the systematic incorporation of stochastic quantization techniques.
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