信号与系统(奥本海默第二版)第7章.pptVIP

Ch 7 Sampling 7.1.1 Impulse-train sampling In frequency domain Sampling Theorem 7.1.2. Sampling with a Zero--order Hold (零阶保持采样) Reconstruction of a signal of the Zero-Order Hold 7.2 Reconstruction ——— interpolation in time domain Band limited interpolation Zero--order Hold Interpolation Examples for the applications of zero-order fold interpolation First-order fold interpolation 7.3 The effect of under-sampling: aliasing Ex. 7.1 Suppose x (t) is sampled at sampling frequency w s, determinate the resulting output of the following system. Particular usage of the aliasing 7.4 Discrete-time processing of continuous-time signals x d [n]= x c (n T)中的频域关系 不同采样率的时/频域关系 Discrete-time processing of continuous-time signals Summary Sampling— Some values or samples are extracted from a signal, at points equally spaced in time. Importance— A continuous-time signal n discrete-time signal Discrete-time signals are preferable to transmitting, processing, inexpensive, lightweight, programmable, easily reproducible Two channels One channel 7.1 Representation of a continuous-time signals by its sampling Sampling needs condition Reconstruction: w s — Niquiste, 奈奎斯特频率（w M ） Ex. The maximum frequency of x1(t), x2(t) are 50Hz, 150Hz, respectively. determinate the minimum sampling frequency of following signals： Zero--order Hold Sampling ： A system samples x (t) at a given instant and holds that value until the next instant at which a sample is taken. Different kinds of interpolation Zero-order hold —— with horizontal line first-order hold —— linear interpolation ( with straight line) Band-limited interpolation —— using ideal lowpass filter Interpolation —— a set of sample values g fit of a continuous signal 内插函数 (a) 脉冲抽样 (b)零级保持-重建 (c )图(a)的1/4间隔抽样， 零级保持-重建 Solution: Sampling oscilloscope 采样示波器: 频闪测速: 旋转圆盘 频闪器 模拟数字转换 数字模拟转换 x d [n]= x c (n T) 中的时域关系 将x c (n T)视为离散时间信号x c [n]涉及了频域尺度变换。