【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。更多还原

【Abstract】 The VLB(IVery 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.更多还原