随机信号 第 一章[精选].pptVIP

* * Example of Digitization Benefit Digitized version enables near-perfect save/cpy/tran. “Sample” voltage at particular rate, save sample using bit encoding Voltage levels still not kept perfectly But we can distinguish 0s from 1s time Volts 0 1 2 3 original signal lengthy transmission (e.g, cell phone) time 0 1 2 3 received signal How fix -- higher, lower, ? lengthy transmission (e.g, cell phone) 01 10 11 10 11 same 01 10 11 10 11 Volts digitized signal time 0 1 a2d Volts 0 1 2 3 d2a time Can fix—distinguish 0s/1s, restore 0 1 Higher sampling rate and more bits per encoding improves re-creation a Not a perfect re-creation due to a2d and d2a * 原始信号 衰减 放大 模拟信号在传输过程中失真 数字信号仍然可以保持 0、1 1.2 Analog versus Digital(模拟与数字) * 1.2 Analog versus Digital(模拟与数字) The problem for Analog signal Easy to be disturb Shift with temperature Hard to be recorded Can not express abstract information * 1.2 Analog versus Digital(模拟与数字) The advantage of digital signal On each data line, the signal is very simple Not influenced by circumstance and device Can be recorded and transmitted easily Any information can be code * 1.2 Analog versus Digital(模拟与数字) Digital system Any inputs and outputs can only be 1 or 0 ! Use logic to determine each output : 1 or 0 ? * 1.2 Analog versus Digital(模拟与数字) Digital Circuits over Analog Ones Reproducibility of Results Ease of design Flexibility, and Functionality Programmability Speed Economy Steadily Advancing Technology * 1.3 Digital Devices (数字器件) Gates（门电路）： —— The most basic digital devices (AND Gate, OR Gate, and NOT Gate or Inverter) [最基本的数字器件（与、或、非门或反相器] Flip-flops（触发器）： —— A device that stores either 0 or 1 (一种能存储 0 或 1 的器件) * 1.3 Digital Devices (数字器件) Figure 1-1 Digital Devices (a) AND Gate (b) OR Gate (c) NOT Gate or Inverter * Basic device in digital system Buffer Truth table Diagram Equation * Basic device in digital system NOT ga