嵌入式系统硬件设计SI基础课件.ppt

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,11/7/2009,#,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,1,*,嵌入式系统硬件设计SI基础,嵌入式系统硬件设计SI基础嵌入式系统硬件设计SI基础,前言,现代电路设计不断朝高速、高密度、低电压、大电流趋势发展，信号完整性（Signal Integrity，SI）、电源完整性（Power Integrity，PI）和电磁兼容（Electromagnetic Compatibility，EMC）问题日益突出传统设计方法显得力不从心，需综合三者间相互影响进行协同设计.,SI挑战,SI问题是电路高速化的产物，电路高速化指电路中信号的有效带宽增加，主要表现在系统工作频率提高和数字信号边沿率加快两方面高速电路常见的SI问题包括：反射（Reflection）、串扰（Crosstalk）、同时开关噪声（SSN，Simultaneous Switching Noise）、时序错位与抖动（Timing Skew&Jitter）等,SI挑战,A digital signal,Frequency 50MHz,Risetime 1ns(10%-90%),Falltime 1ns(10%-90%),Bandwidth 350MHz,Spectrum of a single pulse,10 ns risetime,1 ns risetime,Spectrum of a pulse train,The effect of missing harmonics,1st harmonic only,1st and 3rd harmonic only,1st to 5th harmonic,1st to 21st harmonic,反射,Signal integrity(SI)issue,Interconnect,+,-,I(z,t),I(z,t),V,G,Z,G,Z,L,Transmission line,Load,Thevenin generator,z,0,L,The voltage and current on each point of the line is superposition of a forward and backward voltage,travelling in opposite directions.,The voltage at each point of the line depends on the reflection coefficient at each line terminals:,Transient behavior of voltage at each line terminals:,At generator side(input):,At generator side(input):,Complex transient behavior related to the reflection coefficient on each extremities and transmission line discontinuities,反射解决方法,反射问题主要通过端接匹配解决，使信号在传输过程中感觉不到瞬态阻抗突变。

抖动-实际信号与理想信号间的时序波动，由系统内在噪声和外在噪声共同引起串扰,串扰,-,串扰是指多信号网络间边缘场耦合效应导致的噪声干扰现象串扰,高速电路中需要控制串扰的布线网络主要包括：高速并行总线、高速时钟总线、高速接插件等常用的减小串扰措施包括：减小平行走线长度、增大线间距、采用平面作返回路径、减小互连特性阻抗以及采用防护布线等Basic transmission line,Driver,Transmission line,Termination resistor,The four describing parameters,RResistance per unit length ohm/m,CCapacitance F/m,LInductance H/m,GConductance S/m,Impedance(Z,0,),Impedance is measured in Ohms,Impedance describes the AC resistance a driver will see when driving a signal into a indefinitely long transmission line.,Z,0,=,R,+,L,j,G,+,C,j,For a loss less line this simplifies to:,Z,0,=,L,C,ohm,ohm,Loss(,a,),Loss,a,is measured in dB/m,Loss is the reduction of signal voltage along a line due to resistance and leakage,The,resistive,losses is due to resistance in conductor and ground plane.,The,dielectric,losses is due to the energy needed to change polarization of the dielectric material.,The,radiation,losses is the energy sent from the conductor acting as an antenna.,Resistance at higher frequencies,When the conductor is much thicker than the skin depth one have to substitute the skin depth for the thickness in the resistance formula:,ohm,The resistance has now become frequency dependent!,R,=,1,w,d,s,R,=,1,w,1,f,Skin depth(,d,s,),At higher frequencies only a thin layer of the conductor transport the current.The thickness where the current density is reduced to 1/e is called the skin depth,d,s,.,d,s,=,1,f,m,Skin depth(,d,s,),谢谢,。