基于DDS与PLL的C波段宽带线性扫频源  

C Band Wideband Linear Frequency-Swept Source Based on DDS and PLL

作　　者：刘志强 沈亚飞 王文博[1] 徐金平[1] LIU Zhi-qiang, SHEN Ya-fei, WANG Wen-bo, XU Jin-ping(State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, Chin)

机构地区：[1]东南大学毫米波国家重点实验室

出　　处：《微波学报》2018年第4期71-76,共6页Journal of Microwaves

摘　　要：利用直接数字频率合成（DDS）和锁相环（PLL）技术相结合的混合频率合成方案,研制了一种C波段宽带、高频率分辨率、快速线性扫频的频率源。为了给PLL提供低相位噪声的宽带扫频参考信号,选用ADI的DDS芯片AD9914,并利用阶跃恢复二极管（SRD）高次倍频电路结合二倍频器产生高达3400 MHz的时钟信号。通过上位机配置AD9914内部频率调谐字和数字斜坡发生器,产生512.5-987.5 MHz的扫频参考信号,其频率分辨率可精细到赫兹量级。选用低附加噪声的鉴相器和宽带VCO芯片设计C波段锁相源,在宽带工作频率范围内对DDS扫频信号进行快速跟踪,并有效抑制杂散信号。实测结果表明,该扫频源工作频率为4.1-7.9 GHz,在频率分辨率配置为0.38 MHz时,单向扫频周期为1 ms,扫频线性度为1.58×10-6。单频点输出时相位噪声优于-114 dBc/Hz@10 kHz和-119 dBc/Hz@100 kHz,杂散抑制优于69 dBc。A wideband frequency-swept source at C band with high frequency resolution and high linear sweep speed is developed based on a hybrid scheme of direct digital frequency synthesis（ DDS） and phase locked loop（ PLL） techniques.In order to provide the PLL with a low-phase-noise wideband frequency-swept reference signal,ADI＇s DDS IC AD9914 is chosen in this design. A step recovery diode（ SRD）-based high-order multiplier chain combined with a frequency doubler is employed to generate the DDS＇s clock signal with frequency up to 3400 MHz. By configuring the frequency tuning word and digital ramp generator inside the AD9914,a sweeping reference signal with a frequency range of 512.5-987.5 MHz is generated,with a frequency resolution as fine as Hertz scale. The C band PLL is designed based on a low noise phase-frequency detector and a wideband VCO. The PLL tracks the DDS＇s sweeping signal at a high speed and suppresses the spurious signals effectively in a specified wide frequency range. The measured results show that the operating frequency covers 4.1-7.9 GHz,the one-way sweep period is 1 ms and sweep linearity is 1.58×10-6 when the frequency resolution is configured as 0.38 MHz.The measured phase noise is lower than-114 dBc/Hz@ 10 kHz and-119 dBc/Hz@ 100 kHz,and the spurious suppression is better than 69 dBc for single frequency signals delivered by the frequency source.

关 键 词：直接数字频率合成 锁相环 宽带扫频源 低相位噪声 倍频链 

分 类 号：TN74[电子电信—电路与系统]