【摘要】 VLBI数字基带转换器(Digital Baseband Convertor,简称DBBC)又称为CDAS(Chinese VLBI Data Acquisition System),是上海天文台自主研发的新一代数字化终端设备。该设备可以将宽带信号分成若干个基带信号。由于其结构上采用了多芯片和多板卡结构,使得通道之间的时延存在差异。从设备结构入手,分析了各通道之间时延差异产生的主要原因,提出以复位信号为参考,基于m序列的数据同步方法以解决该问题。通过实验,证明该方法能有效地改善同一中频上各通道间时延的差异。更多还原

【Abstract】 The Chinese VLBI Data Acquisition System(CDAS) independently designed by Shanghai Astronomical Observatory is a digitalized base band convertor for VLBI, which can take the place of traditional analogy base band convertor. It can extract up to 16 channels baseband from 512 MHz bandwidth. The bandwidth of each channel can be selected to be 2, 4, 8, 16 and 32 MHz.The character of the group delay between each channel is important. If the group delay can keep aligning, it will simplify the post data processing. However, due to structure of CDAS – there are several horizontal and longitudinal data streams, which have their own clock regions, it is difficult to keep the group delay aligning among different channels. This paper described the reason why the group delay causes and also the solution how to get alignment of the group delay by adjusting the clock taps of the data inside each FPGA chip. Comparison has been made to show that after adjustment, the difference of group delay among channels in the same IF had been significantly reduced.更多还原