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一、问题的提出一个模拟信号在进行模数变换(A/D)之前,应先通过一个低通滤波器来消除高于1/2采样频率的分量、防止它迭混到低频分量中去.这个滤波器一般称抗迭混滤波器.抗迭混滤波器的性能要求非常高.除了要充分滤除不需要的频率分量外,为了进行频谱分析、要求滤波器的通带相当平坦(通常要求不均匀度小于0.5分贝).作者曾就抗迭混滤波器设计从良好的幅频响应方面进行讨论.另一方面,在用A/D变换记录和再现信号时,是从时域方面进行研究,因此也要考虑抗迭混滤波器的时域响应的问题.一个阶跃信号输入到低通滤波器之后,除了产生一定时间的延迟t_d和一定的上升时间t_r外,还会在顶部有阻尼振荡状的起伏,即有过冲产生.如图1.
First, the question put forward an analog signal before the analog-to-digital conversion (A / D), should first be a low-pass filter to eliminate the component above 1/2 sampling frequency to prevent it from being mixed into the low-frequency components. This filter is generally referred to as an anti-aliasing filter, and the anti-aliasing filter requires very high performance.In addition to sufficiently filtering unwanted frequency components, the filter’s passband is required to be fairly flat for spectral analysis The inhomogeneity is less than 0.5 dB.) The authors have discussed the anti-aliasing filter design in terms of good amplitude-frequency response.On the other hand, when recording and reproducing signals by A / D conversion, , So we should also consider the anti-aliasing filter time-domain response problems.A step signal input to the low-pass filter, in addition to produce a certain time delay t_d and a certain rise time t_r, there will be damping at the top Oscillating ups and downs, that is, there is overshoot.