Use Receiver Equalization to Extend RS485 Data （使用接收方均衡扩展RS485数据）.pdf

Application Report SLLA169 – August 2004 Use Receiver Equalization To Extend RS-485 Data Communications Clark Kinnaird High Performance Analog/Interface Products ABSTRACT Systems designers can use receiver equalization to extend their RS-485 data transmission applications in terms of longer cable distances or higher signaling rates. This application report discusses the benefits of using fixed receiver equalization for specific combinations of signaling rate, cable type, and node-to-node distance. Examples showing discrete implementations and integrated solutions are presented with laboratory results. Contents 1 Introduction 3 2 Problem Statement 3 2.1 Definition of Terms 3 2.2 Sources of Media Losses4 2.2.1 Cable 4 2.3 Typical Cables Recommended for RS-4855 2.4 Measure of Signal Quality 6 3 Possible Solutions 9 3.1 Use Better Cable (Media)9 3.2 Theoretical Methods for Signal Recovery 9 3.3 Driver Preemphasis10 3.4 Receiver Gain Increase11 3.5 Data Coding 12 3.6 Receiver Equalization12 4 Receiver Equalization Implementations 13 4.1 Passive Analog Filters13 4.2 Active Analog Filte