VLBI数字基带转换器的ADC负载性能研究  

Analysis of the Load Performance of ADC in a Digital Baseband Converter for VLBI

作　　者：陈岚[1,2] 罗近涛[1,2] 朱人杰[1,2] 张秀忠[1] 

机构地区：[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

出　　处：《天文研究与技术》2009年第3期191-197,共7页Astronomical Research & Technology

基　　金：国家自然科学基金(10503009)

摘　　要：在研究VLBI数字基带转换器的基础上,对输入给ADC的信号的负载特性详细分析,给出了输入为正弦信号时的ENOB估算公式,分析了输入为天文信号时输入信号的能量对信噪比的影响,推算出了ADC最佳量化时对输入信号负载的要求。In current VLBI systems, signals at radio frequencies （RF）are amplified and downconverted to be at intermediate frequencies （IF）and/or basebands, and are further input to analog-to-digital converters （ADCs） after being appropriately filtered. In these systems, the key components are the ADCs, which must be operated under the condition that their sampling rates are at least twice the bandwidths of received signals, as required by the sampling theorem. In the case that the input signals are the composites of many multiplexed signals, a key factor in the performance of ADCs is the degree of signal clipping, which is carried out when the magnitude of an instantaneous ADC input signal surpasses the maximum range of the ADC. Usually, since at least some clipping is present, the total noise in the ADC output includes the effects from clipping and quantization. A measure of the performance of an ADC is its signal-to-noise ratio（ SNR）, which is defined as the ratio of the average power of the input signal to the average power of noise in the output. This paper gives the formulas to estimate the SNR for the case that the ADC input signal is sinusoidal based on the detailed analysis of the load performance of an ADC. The paper further analyzes the effects of powers of input signals on the SNR when the input signal is of real astronomical origin, which defines the requirements on signal loading under the best quantization of an ADC.

关 键 词：天文观测设备与技术 甚长基线测量 A/D转换器 SNR 

分 类 号：TP335.1[自动化与计算机技术—计算机系统结构]