论文标题
优化用于放射媒介观测的数字光谱仪
Optimizing digital spectrometers for radioastronomical observations
论文作者
论文摘要
本文的目的是制定一个过程来优化镜像抑制，从而减少了快速傅立叶变换光谱仪（FFTS）的动态范围，并在FFT的现场可编程门阵列（FPGA）中实现此过程。这是通过在复杂振幅光谱上应用校准来实现的。现代的多光束杂项接收器配备了大量独立信号链，这导致了一个复杂的系统，该系统消耗了空间和功率，而且价格昂贵。为了降低接收器阵列的复杂性，中间频率（if）频段为4-8 GHz，这需要FFTS直接采样此频段。 当前FFT的4 GHz的输入带宽不能用单个模拟数字转换器（ADC）采样。为了达到该带宽，多个ADC在不同时间点采样相同的信号。该方法称为时间交织的采样\“。ADC的特征彼此不同，这会导致镜像信号在频谱中。这些镜像信号可以减少光谱仪的动态范围。因此，不匹配的不匹配必须被主动校正。因此，FFT的当前产生使用频率为频率，这是频率的频率，而不是在一个频率频率上进行频率，这是一个固定的频率。它们的影响随频率增加。 在本文工作中开发的过程涉及三个步骤。首先，不匹配是通过频段测量的。然后，使用时间交织的ADC模型从这些不匹配中计算过滤系数。然后将这些滤波器系数应用于ADC的复杂振幅光谱。与频率独立校准相比，新实施的校准可改善20 dB的镜像抑制作用。
The goal of this thesis was to develop a procedure to optimize the mirror suppression, which reduces the dynamic range of the Fast Fourier Transform spectrometers (FFTS), and implement this procedure in the Field Programmable Gate Array (FPGA) of the FFTS. This is achieved by applying a calibration on the complex amplitude spectrum. Modern multi-beam heterodyne receivers are equipped with a large number of independent signal chains, which leads to a complex system that consumes space as well as power and is expensive. To reduce the complexity of the receiver array the intermediate frequency (IF) band is 4-8 GHz, which requires the FFTS to sample this band directly. The input bandwidth of 4 GHz of the current generation of FFTS cannot be sampled with a single analog-digital converter (ADC). To reach that bandwidth, multiple ADCs sample the same signal at different points in time. The method is called time interleaved sampling\". The characteristics of the ADCs differ from each other, which leads to mirror signals in the spectrum. These mirror signals can reduce the dynamic range of the spectrometers. Therefore the mismatches must be actively corrected. The current generation of FFTS use a frequency independent calibration, which optimizes the mirror suppression at one fixed frequency. This it is not optimal as some of the mismatches are frequency dependent and their impact increases with frequency. The procedure developed during this thesis work involves three steps. First the mismatches are measured over the frequency band. Then filter coefficients are calculated from these mismatches using a model of a time interleaved ADC. These filter coefficients are then applied to the complex amplitude spectra of the ADCs. The newly implemented calibration improves the mirror suppression up to 20 dB compared to the frequency independent calibration.
