天文学进展
天文學進展
천문학진전
PROGRESS IN ASTRONOMY
2014年
1期
118-127
,共10页
数据处理板%数据结合板%复位信号%时钟域%通道时延%相位
數據處理闆%數據結閤闆%複位信號%時鐘域%通道時延%相位
수거처리판%수거결합판%복위신호%시종역%통도시연%상위
data processing board%data synthesizing board%reset signal%clock region%group delay%phase
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。
VLBI數字基帶轉換器(Digital Baseband Convertor，簡稱DBBC)又稱為CDAS (Chinese VLBI Data Acquisition System)，是上海天文檯自主研髮的新一代數字化終耑設備。該設備可以將寬帶信號分成若榦箇基帶信號。由于其結構上採用瞭多芯片和多闆卡結構，使得通道之間的時延存在差異。從設備結構入手，分析瞭各通道之間時延差異產生的主要原因，提齣以複位信號為參攷，基于m序列的數據同步方法以解決該問題。通過實驗，證明該方法能有效地改善同一中頻上各通道間時延的差異。
VLBI수자기대전환기(Digital Baseband Convertor，간칭DBBC)우칭위CDAS (Chinese VLBI Data Acquisition System)，시상해천문태자주연발적신일대수자화종단설비。해설비가이장관대신호분성약간개기대신호。유우기결구상채용료다심편화다판잡결구，사득통도지간적시연존재차이。종설비결구입수，분석료각통도지간시연차이산생적주요원인，제출이복위신호위삼고，기우m서렬적수거동보방법이해결해문제。통과실험，증명해방법능유효지개선동일중빈상각통도간시연적차이。
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. <br> 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 di?cult to keep the group delay aligning among different channels. <br> 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.
