计算机工程与应用 ›› 2010, Vol. 46 ›› Issue (2): 55-59.DOI: 10.3778/j.issn.1002-8331.2010.02.018

• 研发、设计、测试 • 上一篇    下一篇

频率可调带宽可选的VLBI多相数字基带转换器

陈 岚1,2,罗近涛1,2,项 英1,张秀忠1   

  1. 1.中国科学院 上海天文台,上海 200030
    2.中国科学院 研究生院,北京100049
  • 收稿日期:2009-09-14 修回日期:2009-10-16 出版日期:2010-01-11 发布日期:2010-01-11
  • 通讯作者: 陈 岚

Polyphase based VLBI digital baseband converter with adjustable IF center frequency and bandwidth

CHEN Lan1,2,LUO Jin-tao1,2,XIANG Ying1,ZHANG Xiu-zhong1   

  1. 1.Shanghai Astronomical 0bservatory,Chinese Academy of Sciences,Shanghai 200030,China
    2.Graduate University of Chinese Academy of Sciences,Beijing 100049,China
  • Received:2009-09-14 Revised:2009-10-16 Online:2010-01-11 Published:2010-01-11
  • Contact: CHEN Lan

摘要: VLBI数据采集终端是VLBI台站的重要设备,近年来随着数字硬件设备例如ADC、DSP、FPGA的快速发展,数字基带转化器代替模拟基带转换器成为现实。现有采用多相滤波器实现DBBC的方法不可避免存在盲区,且频率、带宽均不可调。提出一种通用的基于多相结构的宽带数字下变频方法,将多速率信号处理和并行处理方法应用在其中,成功实现了VLBI多个通道的单边带数字基带转换,且能实现中频中心频率可调、带宽可选。硬件测试结果表明VLBI数字基带转换器频率设置正确,带宽选择正确,且数字基带转换器带通特性好于模拟基带转换器。

关键词: 甚长基线干涉测量, 数字基带转换器, 单边带, 多相滤波器组, 盲带, 现场可编程门阵列

Abstract: The VLBI(Very Long Baseline Interferometry) data acquisition backend plays an important role in the VLBI station.Recently,based on advances in digital hardware like ADC(Analog-to-Digital Conversion),DSP(Digital Signal Processing),FPGA(Field Programmable Gate Arrays) and so on,it has become practical to sample and digitally process the intermediate frequency signal directly.DBBC(Digital Base-Band Converters) will replace ABBC(Analog Base Band Converters) in the VLBI data acquisition backend.A VLBI digital backend using poly-phase filter banks exits blind frequency zone inevitably.Moreover,the frequency and the band width are not adjustable in this method.This paper analyzes this limitation and presents a sequence of simple modifications to sampled data structures based on the analog prototype system to obtain the poly-phase structure in the VLBI data acquisition backend which can eliminate the blind frequency zone.The theoretical principles of digital SSB(Single Side Band) converters are discussed in detail.The approach adopts multi-rate signal processing for the designed filters in a digital SSBconverter which is carried out by virtex-4 FPGA chips.The result of hardware VLBI experiments indicate that it can receive random IF band-pass in and bandwidth can be selected.Meanwhile,a conclusion is reached from the experiment that the VLBI DBBC has a better band pass performance than the ABBC.

Key words: Very Long Baseline Interferometry(VLBI), digital base-band converter, Single Side Band(SSB), poly-phase filter banks, blind frequency zone, Field Programmable Gate Arrays(FPGA)

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