高速数字电路设计及EMC设计

高速数字电路设计及EMC设计。 目 录  1. 高速数字电路设计.......................................................................................................................... 5  1.1 何谓高速数字信号 ..................................................................................................................5  1.2 微带线 带状线的概念..............................................................................................................5  1.2.1 微带线 Microstrip ......................................................................................................5  1.2.2 带状线 Stripline .........................................................................................................6  1.2.3 经验数据...........................................................................................................................6  1.2.4 同轴线 coaxial cable ..................................................................................................6  1.2.5 双绞线 twisted-pair cable ..........................................................................................7  1.2.6 等间隔的电容负载的影响...............................................................................................7  1.3 常见高速电路.............................................................................................................................8  1.3.1 ECL Emitter Coupled Logic 电路...............................................................................8  1.3.2 CML Current Mode Logic 电路.................................................................................9  1.3.3 GTL Gunning Transceiver Logic 电路.....................................................................10  1.3.4 BTL Backplane Transceiver Logic 电路..................................................................10  1.3.5 TTL Transistor Transistor Logic 电路......................................................................11  1.3.6 模数转换电路 线接收器............................................................................................12  1.4 常见电路匹配措施...................................................................................................................12  1.4.1 反射.................................................................................................................................12  1.4.2 终端匹配.........................................................................................................................13  1.4.3 始端匹配.........................................................................................................................15  1.5 高速电路设计一般原则和调试方法.......................................................................................16  1.5.1 同步逻辑设计.................................................................................................................16  1.5.2 了解选用器件的输入 输出结构 选用恰当的匹配电路 在考虑节省功耗 电路 又 能容许的情况下 可适当地引入失配 ..............................................................................19  1.5.3 对极高速率 300MHz 以上 的信号 一般建议选用互补逻辑 以降低对电源的要 求 ..........................................................................................................................................19  1.5.4 了解每一根高速信号电流的流向 电流环 .............................................................19  1.5.5 信号的布线 电源和地层的分割 是否符合微带线 带状线的要求 高速信号要 有回路地相配 不是屏蔽地 ..............................................................................................19  1.5.6 电源滤波.........................................................................................................................19  1.5.7 对很高速度的信号要估算其走线延迟 .....................................................................19  1.5.8 在满足速度要求的前提下 尽量选用工作速率低的器件 .....................................19  1.5.9 差分线尽量靠近走线.....................................................................................................19  1.5.10 测试方法 选择有 50 输入的高速示波器 一般自制一个探头 测量点应尽量靠 近所观察的位置或者需要该信号的实际位置 一般不建议测输出端的信号波形 与实际  2 使用的位置有一定差别 ......................................................................................................19  1.5.11 ringing, crosstalk, radiated noise —— 数字系统的三种噪声....................................19  1.5.12 数字信号的绝大部分能量 功率谱密度 集中在 fknee之内...................................19  1.5.13 延时 FR4 PCB outer trace: 140~180 ps/inch inner trace: 180 ps/inch ..........20   1.5.14 集总参数与分布参数系统..........................................................................................20  1.5.15 互感 耦合电容的作用 干扰 ..............................................................................20  1.5.16 ECL电路的上升时间 下降时间的计算..................................................................20  1.5.17 在数字系统中 耦合电容引起的串扰比起互感引起的串扰要小 ......................21  1.5.18 传输通道包括器件封装 PCB 布局 连接器 至少在 fknee 的范围内要有平坦的 频响 以保证信号不失真 否则信号在收端可能会遇到上升时间劣化 过冲 振铃 lump 等现象 ..................................................................................................................................21  1.5.19 阻容负载对电流变化的作用......................................................................................21  1.5.20 噪声容限 noise immunity 以 10H189 器件为例................................................22   1.5.21 地反弹 ground bounce .......................................................................................23  1.5.22 寄生电容 Stray Capacitance 的影响 对于高输入阻抗电路影响尤为严重...........23  1.5.23 示波器探针的电气模型..............................................................................................24  1.5.24 21:1 探针 ...................................................................................................................25  1.5.25 趋肤效应 skin effect 在高频时导线表面附近的电流密度加大 而中心部分的 电流密度减小 趋肤效应使得导线对高频信号的衰减增大 趋肤效应的频率与导体的材 料有关 ..................................................................................................................................25  1.5.26 对低频信号 电流流经电阻最小的路径 对高频信号 回流路径的电感远比其电 阻重要 高频电流流经电感最小的路径 而非电阻最小的路径 最小电感回流路径正好 在信号导线的下面 以减小流出和流入电流通路间的环路面积 ..................................25  1.5.27 负载电容对上升时间的影响......................................................................................26  1.5.28 直流匹配和交流匹配的功耗比较..............................................................................27  1.5.29 电源系统设计原则......................................................................................................27  1.5.30 TTL和 ECL 的混合系统要注意.................................................................................27  1.5.31 电源线上的电磁辐射防护..........................................................................................28  1.5.32 旁路电容的选取和安装 ..........................................................................................28  1.5.33 连接器对高速系统的影响..........................................................................................28  1.5.34 总线 ..........................................................................................................................30  2 电磁兼容性 Electromagnetic Compatibility ........................................................................... 32  2.1 关于电磁兼容性的基本原理...................................................................................................32  2.1.1 下面的电路布局有什么问题 .....................................................................................32  2.1.2 走线可穿过回流平面的缝隙吗 No .......................................................................33  2.1.3 走线的电感和电容.........................................................................................................33  2.1.4 接地的作用 .................................................................................................................34  2.1.5 信号参考点应在何处接至基底(chassis)......................................................................35  2.1.6 周期信号........................................................................................................................36   3 2.1.7 EMC 三要素...................................................................................................................36  2.1.8 共模和差模.....................................................................................................................38  2.1.9 减小噪声的措施............................................................................................................39  2.2 信号完整性――减小串扰和信号畸变...................................................................................39  2.2.1..........................................................................................................................................39  2.2.2 屏蔽................................................................................................................................40  2.2.3 信号畸变........................................................................................................................41  2.3 通过滤波减小直流电源噪声...................................................................................................41  2.3.1..........................................................................................................................................42  2.3.2 If DC power planes can’t be used, then lumped decoupling capacitors must be sized and  placed correctly. .......................................................................................................................42  2.3.3 多层 PCB 表贴电容 串联电感在何处 ...............................................................43  2.3.4 How to distribute DC power from a single supply to both analog and digital circuits?..43  2.4 元件放置与信号层分配...........................................................................................................44  2.5 Reducing conducted & radiated emission & susceptibility........................................................46  2.6 电路板 EMC 准则总结............................................................................................................48  2.6.1 Component Placement ....................................................................................................48  2.6.2 DC Power Distribution....................................................................................................48  2.6.3 Routing of Signal Output and Return Paths....................................................................49  2.6.4 Signal Integrity – Reducing Crosstalk and Distortion.....................................................49  2.6.5 High Frequency Transmission Lines...............................................................................50  2.6.6 Reducing Conducted and Radiated Emissions................................................................50