zh-cnGoodspeed Rss5Fri, 09 Jan 2009 01:27:37 GMTFri, 10 Oct 2008 11:50:47 GMThttp://www.sichinamag.com/blog/pcbsu/37197/message.aspx<p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 24.1pt; LINE-HEIGHT: 18pt; TEXT-ALIGN: center; mso-char-indent-count: 2.0; mso-line-height-rule: exactly" align="center"><b><span style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">印制电路板的版面设计要求</span></b><b><span lang="EN-US" style="FONT-SIZE: 12pt"><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></span></b></p> <p style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 18pt; LINE-HEIGHT: 18pt; mso-char-indent-count: 2.0; mso-line-height-rule: exactly"><span style="FONT-SIZE: 9pt"><font face="宋体">在常用的印制<span lang="EN-US"><a href="http://www.zxpcb.net/"><span lang="EN-US"><span lang="EN-US">电路板</span></span></a></span>类型中，版面设计应注意的事项详细说明如下</font><font face="宋体"><span lang="EN-US">:<br>1)</span>单面板<span lang="EN-US">:</span>在成本要求较低的情况下通常使用这种类型的面板。在<span lang="EN-US">PCB</span>抄板版面设计时，有时需要元器件或使用跨接线来跳过电路板抄板的走线。如果数量太多，就应考虑使用<span lang="EN-US">PCB</span>双面板。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 18pt; LINE-HEIGHT: 18pt; mso-char-indent-count: 2.0; mso-line-height-rule: exactly"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 9pt">2) PCB</span><span style="FONT-SIZE: 9pt">抄板双面板<span lang="EN-US">:</span>双面板可以使用也可以不使用<span lang="EN-US">PTH </span>。因为<span lang="EN-US">PTH </span>板的价格昂贵，当电路的复杂度和密度需要时才会使用。在<span lang="EN-US">PCB</span>版面设计中，元器件面的导线数量必须保持最少，以确保容易获得所需用材。在<span lang="EN-US">PTH</span>板中，镀通孔仅用于电气连接而不用于元器件的安装。出于经济和可靠性方面的考虑，孔的数量应保持在最低限度。要选择单面板还是双面板，很重要的一点，要考虑到元器件的表面面积<span lang="EN-US">(C) </span>，它与印制电路板的总面积<span lang="EN-US">(S) </span>之比为一个适当的恒定比例，这对于元器件的安装是有用的。值得注意的是<span lang="EN-US">US" </span>通常指的是面板一面的面积。表<span lang="EN-US">3-2</span>列出了最常用的印制电路板的<span lang="EN-US">S : C </span>的比率范围。可以把表<span lang="EN-US">3-2 </span>中列出的数值作为设计准则，它仅仅为导线宽度、焊盘直径、最小剩余空间等的选择提供了一个标准。<span lang="EN-US"><o:p></o:p></span></span></font></p> <p style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 18pt; LINE-HEIGHT: 18pt; mso-char-indent-count: 2.0; mso-line-height-rule: exactly"><span style="FONT-SIZE: 9pt"><font face="宋体">　　一般情况下，选择<span lang="EN-US"><a href="http://www.sichinamag.com/blog/pcbchaobanxl/">PCB</a></span>单面板还是双面板必须满足最有效的成本利用。根据经验，带有镀通孔的双面印制板的造价是单面板的<span lang="EN-US">5 -10 </span>倍之多。同样，装配元器件的成本也是一个需要考虑的重要方面，装配一个单面印制电路板的元器件<span lang="EN-US">(</span>手工<span lang="EN-US">)</span>所需的费用大约是电路板成本的<span lang="EN-US">25% -50% </span>，而装配一个带<span lang="EN-US">PTH </span>的双面印制电路板的元器件，所需费用则为其成本的<span lang="EN-US">15% -30%</span>。印制电路板不仅提供了机械支持，而且还对安装在它上面的元器件起到了连接作用。因此，对于印制电路板的设计者来说，有必要了解面板的整个物理尺寸<span lang="EN-US">(</span>外框尺寸<span lang="EN-US">)</span>、安装孔的位置、高度限制和相关的详细资料。以下就是印制电路板<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="MARGIN: 0cm 0cm 0pt; TEXT-INDENT: 18pt; LINE-HEIGHT: 18pt; mso-char-indent-count: 2.0; mso-line-height-rule: exactly"><span style="FONT-SIZE: 9pt"><font face="宋体">机械设计中主要要考虑的因素</font><font face="宋体"><span lang="EN-US">:<br>1 )</span>适合于印制电路板制作的最佳面板尺寸</font><font face="宋体"><span lang="EN-US">;<br>2) </span>面板安装孔、支架、夹板、夹子、屏蔽盒和散热器的位置</font><font face="宋体"><span lang="EN-US">;<br>3) </span>对于较重元器件合适的固定装置</font><font face="宋体"><span lang="EN-US">;<br>4) </span>元器件安装的合适孔径</font><font face="宋体"><span lang="EN-US">;<br>5) </span>装配好的电路板在运输过程中要具有抗压性和抗震性</font><font face="宋体"><span lang="EN-US">;<br>6) </span>电路板的装配方式<span lang="EN-US">(</span>垂直安装<span lang="EN-US">/</span>水平安装</font><font face="宋体"><span lang="EN-US">) ;<br>7) </span>冷却方式</font><font face="宋体"><span lang="EN-US">;<br>8) </span>元器件特殊的放置要求，类似于在前面板上操作的元器件，例如<span lang="EN-US">:</span>按钮、变阻器等。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: left" align="left"><span lang="EN-US">PCB</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">抄板相关资料详见：</span><u><span lang="EN-US" style="COLOR: blue">http://webliver.com/u/pcbandyxl/Blog/Default.aspx<o:p></o:p></span></u></p>http://www.sichinamag.com/blog/pcbsu/37197/message.aspx IC设计与软件Sat, 06 Sep 2008 15:48:54 GMThttp://www.sichinamag.com/blog/pcbsu/32173/message.aspx<h1 style="MARGIN: auto 0cm; LINE-HEIGHT: 130%; TEXT-ALIGN: center" align="center"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%">PCB</span><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%">抄板工程师教你如何增强防静电<span lang="EN-US">ESD</span>功能<span lang="EN-US"><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></span></span></font></h1> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">在<span lang="EN-US">PCB</span>板的设计当中，可以通过分层、恰当的布局布线和安装实现<span lang="EN-US">PCB</span>的抗<span lang="EN-US">ESD</span>设计。在设计过程中，通过预测可以将绝大多数设计修改仅限于增减元器件。通过调整<span lang="EN-US">PCB</span>布局布线，能够很好地防范<span lang="EN-US">ESD</span>。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">来自人体、环境甚至电<b style="mso-bidi-font-weight: normal"><span lang="EN-US"><a href="http://www.zxpcb.net/" target=_blank>PCB<span lang="EN-US"><span lang="EN-US">抄板</span></span></a></span></b>子设备内部的静<span lang="EN-US">PCB</span>抄板电对于精密的半导体芯片会造成各种损伤，例如穿透元器件内部薄的绝缘层；损毁<span lang="EN-US">MOSFET</span>和<span lang="EN-US">CMOS</span>元器件的栅极；<span lang="EN-US">CMOS</span>器<span lang="EN-US">PCB</span>抄板件中的触发器锁死；短路反偏的<span lang="EN-US">PN</span>结；短路正<span lang="EN-US">PCB</span>抄板向偏置的<span lang="EN-US">PN</span>结；<span lang="EN-US">PCB</span>抄板熔化有源器件内<span lang="EN-US">PCB</span>抄板部的焊接线或铝线。为了消除静电释放<span lang="EN-US">(ESD)</span>对电子设备的干扰和破坏，需要采取多种技术手段进行防范。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">在<span lang="EN-US">PCB</span>板的设计当中，可以通过分层、恰当的布局<span lang="EN-US">PCB</span>抄板<span lang="EN-US">PCB</span>抄板布线和安装实现<span lang="EN-US">PCB</span>的抗<span lang="EN-US">ESD</span>设计。在设计过程中，通过预测可以将绝大多数设计修改仅限于增减元器件。通过调整<span lang="EN-US">PCB</span>布局布线，能够很<span lang="EN-US">PCB</span>抄板好地防范<span lang="EN-US">PCB</span>抄板<span lang="EN-US">ESD</span>。以下是一些常见的防范措施。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">尽可能使用多层<span lang="EN-US">PCB</span>，相对于双面<span lang="EN-US">PCB</span>而言，地平面和电源平面，以及排列紧密的信号线<span lang="EN-US">-</span>地线间距能够减小共模阻抗和感性耦合，使之达到双面<span lang="EN-US">PCB</span>的<span lang="EN-US">1/10</span>到<span lang="EN-US">1/100</span>。尽量地将每一个信号层都紧靠一个电源层或地线层。对于顶层和底层表面都有<span lang="EN-US"><a href="http://www.pcbboke.cn/" target=_blank><span lang="EN-US"><span lang="EN-US"><font color="#828282">元器件</font></span></span></a></span>、具有很短连接线以及许多填充地的高密度<span lang="EN-US">PCB</span>，可以考虑使用内层线。对于双面<span lang="EN-US">PCB</span>来说，要采用紧密交织的电源和地栅格。电源线紧靠地线，在垂直和水平线或填充区之间，要尽可能多地连接。一面的栅格<span lang="EN-US">PCB</span>抄板尺寸小于等于<span lang="EN-US">60mm</span>，如果可能，栅格尺寸应小于<span lang="EN-US">13mm</span>。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">确保每一个电路<span lang="EN-US">PCB</span>抄板尽可能紧凑。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">尽可能将所有连接器都放在一边。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">如果可能，将电源<span lang="EN-US">PCB</span>抄板线从卡的中央引入，并远离容易直接遭受<span lang="EN-US">ESD</span>影响的区域。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">在引向机箱外的连接器<span lang="EN-US">(</span>容易<span lang="EN-US">PCB</span>抄板直接被<span lang="EN-US">ESD</span>击中<span lang="EN-US">)</span>下方的所有<span lang="EN-US">PCB</span>层上，要放置宽的机箱地或者多边形填充地，并每隔大约<span lang="EN-US">13mm</span>的距离用过孔将它们连接在一起。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">在卡的边缘上放<span lang="EN-US">PCB</span>抄板置安装孔，安装孔周围用<span lang="EN-US">PCB</span>抄板无阻焊剂的顶层和底层焊盘连接到机箱地上。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%">PCB</span><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%">装配时，不要在顶层或者底层的<span lang="EN-US">PCB</span>抄板焊盘上涂覆任何焊料。使用具有内嵌<span lang="EN-US">PCB</span>抄板垫圈的螺钉来实现<span lang="EN-US">PCB</span>与金属机箱<span lang="EN-US">PCB</span>抄板<span lang="EN-US">/</span>屏蔽层或接地面上支架的紧密接触。<span lang="EN-US"><o:p></o:p></span></span></font></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">在每一层的机箱地和电路地之间，要设置相同的“隔离区”；如果可能，保持间隔距离为<span lang="EN-US">0.64mm</span>。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">在卡的顶层和底层靠近<span lang="EN-US">PCB</span>抄板安装孔的位置，每隔<span lang="EN-US">100mm</span>沿机箱地线将机箱地和电路地用<span lang="EN-US">1.27mm</span>宽的线连接在一起。与这些连接点的相邻处，在机箱地和电路地<span lang="EN-US">PCB</span>抄板之间放置用于安装的焊盘或安装孔。这些地线连接可以用刀片划开，以保持开路，或用磁珠<span lang="EN-US">/</span>高频电容的跳接。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">如果电路板不会放入金属机箱或者<span lang="EN-US">PCB</span>抄板屏蔽装置中，在电路板的顶层和底层机箱地线上不能涂阻焊剂，这样它们可以作为<span lang="EN-US">ESD</span>电弧的放电极。<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">要以下<span lang="EN-US"><a href="http://www.pcbon.net/PCBChaoBan/index.asp" target=_blank>PCB<span lang="EN-US"><span lang="EN-US">抄板</span></span></a></span>列方式在电路周围设置一个环形地：<span lang="EN-US"><o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span lang="EN-US" style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">(1)</font></span><span style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">除边缘连接<span lang="EN-US">PCB</span>抄板器以及机箱地以外，在整个外围四周放上环形地通路。</font><font face="宋体"><span lang="EN-US"> <br>(2)</span>确保所有层的环形地宽度大于<span lang="EN-US">2.5mm</span>。</font><span lang="EN-US"><br><font face="宋体">(3)</font></span><font face="宋体">每隔<span lang="EN-US">13mm</span>用过孔将环形地连接起来。</font><span lang="EN-US"><br><font face="宋体">(4)</font></span><font face="宋体">将环形地与多层<span lang="EN-US">PCB</span>抄板电路的公共地连接到一起。</font><span lang="EN-US"><br><font face="宋体">(5)</font></span><font face="宋体">对安装在金属机箱或者屏蔽装置里的双面<span lang="EN-US">PCB</span>抄板来说，应该将环形地与电路公共地连接起来。不屏蔽的双面电路则应该将环形地连接到机箱地，环形地上不能涂阻焊剂，以便该环形地可以充当<span lang="EN-US">ESD</span>的放电棒，在环形地<span lang="EN-US">(</span>所有层<span lang="EN-US">)</span>上的某个位置处至少放置一个<span lang="EN-US">0.5mm</span>宽的间隙，这样可以避免<span lang="EN-US">PCB</span>抄板形成一个大的环路。信号布线离环形地的距离不能小于<span lang="EN-US">0.5mm</span>。<span lang="EN-US"> <o:p></o:p></span></font></span></p> <p style="LINE-HEIGHT: 130%"><span lang="EN-US" style="FONT-SIZE: 9pt; LINE-HEIGHT: 130%"><font face="宋体">&nbsp;<o:p></o:p></font></span></p> <p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 9pt"><o:p>&nbsp;</o:p></span></p>http://www.sichinamag.com/blog/pcbsu/32173/message.aspx IC设计与软件Tue, 02 Sep 2008 09:40:48 GMThttp://www.sichinamag.com/blog/pcbsu/31608/message.aspx<p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: center" align="center"><b style="mso-bidi-font-weight: normal"><span style="FONT-SIZE: 14pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial">如何提高提高<span lang="EN-US">PCB</span>设备可靠性<span lang="EN-US"><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></span></span></b></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">提高<span lang="EN-US"><a href="http://www.pcb-sz.com/">PCB</a></span>设备可靠性的技术措施<span lang="EN-US">:</span>方案选择、<span lang="EN-US">PCB<a href="http://www.pcbboke.cn/"><span lang="EN-US" style="COLOR: #0059d1; TEXT-DECORATION: none; text-underline: none"><span lang="EN-US">电路设计</span></span></a></span>、<span lang="EN-US">PCB</span>电路板设计、结构设计、元器件选用、制作工艺等多方面着手，具体措施如下：<span lang="EN-US"><br></span><b>（<span lang="EN-US">1</span>）简化方案设计。<span lang="EN-US"><br></span></b>方案设计时，在确保设备满足技术、性能指标的前提下，应尽量简化设计，简化电路和结构设计，使每个部件都成为最简设计。当今世界流行的模块化设计方法是提高设备可靠性的有效措施。块功能相对单一，系统由模块组成，可以减少设计的复杂性，将设计标准化、规范化。国内外大量事实已证明了这一点，产品设计应采用模块化设计方法。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">2</span>）采用模块和标准部件。</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">模块和标准部件是经过大量试验和广泛使用后证明为高可靠性的产品，因而能充分消除设备的缺陷和隐患，也为出现问题之后的更换和修理带来了方便。采用模块和标准化产品不仅能有效地提高设备的可靠性，而且能大大缩短研制周期，为设备的迅速改型与列装提供极有利的条件。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">3</span>）提高集成度</span></b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">。<span lang="EN-US"><br></span>选用各种功能强、集成度高的大规模、超大规模集成电路，尽量减少元器件的数量。元器件越少，产生隐患的点也越少。这样，不仅能提高设备的可靠性，而且。能缩短研制、开发周期。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">4</span>）降额设计。</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">降额设计是指元器件在低于其额定应力的条件下工作，是降低元器件失效率的有效方法，因此，设汁时在确保技术性能指标的前提下，对元器件的工作电压范围、温度特性、电特性参数等都采取降额使用的方法，从而降低元器件在各种应力条件下的失效率。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">降额设计，不同的元器件所要考虑的因素是不一样的：有的是电压范围，有的是电流大小，有的是温度，有的是频率，有的是振动等等。一般情况下，对电容的耐压、频率、温度特性，电阻的功率，电感的电流及频率特性，二极管、三极管、可控硅、运算放大器、驱动器、门电路等器件的结电流、结温或扇出系数，电源的开关和主供电源线缆的耐电压<span lang="EN-US">/</span>电流和耐温性能，信号线缆的频率特性，还有散热器、接插件、模块电源等器件的使用，要求进行降额设计。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">5</span>）选择优质器件。</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">元器件是设备的基本组成单元，其质量的好坏将直接影响到设备的可靠性。军用通信设备应尽量采用工业级以上产品，最好是军品，并在上机前严格进行老化筛选，剔除早期失效器件。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">6</span>）充分利用软件资源。</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">由于软件编程的灵活性，在设计中应充分利用软件资源。目前软件的调试手段和工具相对较多，对故障和设计问题容易定位，解决周期相对较短。充分利用软件资源是提高可靠性的一个重要方法。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">7</span>）结构可靠、工艺成熟、先进。</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">在<span lang="EN-US"><a href="http://www.x5dj.com/pcbpcbsxl/">PCB</a></span>电路、结构设计中，应尽量减少接插件、金属化孔的数量，电路器件和芯片尽量采用直接在印制板上焊接的方法，选用表面贴装器件，采用表面贴装技术，以避免接触不良，确保设备的可靠性。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">8</span>）热设计。<span lang="EN-US"><br></span></span></b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">过高的温度是引起设备性能和可靠性降低的重要因素之一，为此应采取热防护措施控制和降低设备工作时的温升，保证设定良好的散热，提高设备的热可靠性。<span lang="EN-US"><br></span>过低的温度，也会引起设备性能和可靠性降低，有的元器件在环境温度太低时不能正常工作。所以在低温环境中使用的设备，也要进行低温测试。在设计时必须考虑设备工作的温度条件和环境。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">9</span>）电磁兼容性设计。</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">设备工作时会受到许多电磁场的干扰，有自然的也有人为的。军用设备更是如此，现代高科技电子对抗战中，一个很重要的技术手段就是局部发射高能量的电磁波，以破坏对方设备中的元器件，从而使设备工作失灵。为此应采取有效的屏蔽、滤波等防干扰措施以防止噪声、干扰电磁场对设备的干扰，确保设备工作可靠。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">10</span>）抗振冲设计。</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">设备在使用、运输过程中会受到各种各样振动、冲击的影响，从而影响其可靠性，为此应提高设备的机械强度和刚度，并采取减振缓冲措施，以加强设备抗振动、冲击的能力，提高设备的可靠性。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">11</span>）采用故障指示装置。<span lang="EN-US"><br></span></span></b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">设计故障检测电路及故障报警装置，以便及时发现故障，从而缩短设备的故障检修时间。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">12</span>）操作简单、维修方便。<span lang="EN-US"><br></span></span></b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">设备中操作、维修的功能是保证设备可靠性的主要因素之一。设计中，应尽量采用插入单元、模块，同时采用模块化、标准化结构和快速拆卸结构，以利于操作和维修。事实证明，设备采用模块化结构能大大简化操作，方便维修。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: center" align="center"><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"><o:p>&nbsp;</o:p></span></p>http://www.sichinamag.com/blog/pcbsu/31608/message.aspx IC设计与软件Tue, 02 Sep 2008 09:40:09 GMThttp://www.sichinamag.com/blog/pcbsu/31607/message.aspx<p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: center" align="center"><b style="mso-bidi-font-weight: normal"><span style="FONT-SIZE: 14pt; COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">如何设计一块优良的</span></b><b style="mso-bidi-font-weight: normal"><span lang="EN-US" style="FONT-SIZE: 14pt; COLOR: black; FONT-FAMILY: Arial">PCB</span></b><b style="mso-bidi-font-weight: normal"><span style="FONT-SIZE: 14pt; COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">抄板</span></b><b style="mso-bidi-font-weight: normal"><span lang="EN-US" style="FONT-SIZE: 14pt; COLOR: black; FONT-FAMILY: Arial"><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></span></b></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">大家都知道理做<span lang="EN-US"><a href="http://www.zxpcb.net/">PCB<span lang="EN-US"><span lang="EN-US">抄</span></span><span lang="EN-US"><span lang="EN-US">板</span></span></a></span>就是把设计好的原理图变成一块实实在在的<span lang="EN-US">PCB</span>电路板<span lang="EN-US">,</span>请别小看这一过程<span lang="EN-US">,</span>有很多原理上行得通的东西在工程中却难以实现<span lang="EN-US">,</span>或是别人能实现的东西另一些人却实现不了<span lang="EN-US">,</span>因此说做一块<span lang="EN-US">PCB</span>板不难<span lang="EN-US">,</span>但要做好一块<span lang="EN-US">PCB</span>板却不是一件容易的事情。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">微电子领域的两大难点在于高频信号和微弱信号的处理<span lang="EN-US">,</span>在这方面<span lang="EN-US">PCB</span>制作水平就显得尤其重要<span lang="EN-US">,</span>同样的原理设计<span lang="EN-US">,</span>同样的元器件<span lang="EN-US">,</span>不同的人制作出来的<span lang="EN-US"><a href="http://www.x5dj.com/pcbpcbsxl/">PCB</a></span>就具有不同的结果<span lang="EN-US">,</span>那么如何才能做出一块好的<span lang="EN-US">PCB</span>板呢<span lang="EN-US">?</span>根据我们以往的经验<span lang="EN-US">,</span>想就以下几方面谈谈自己的看法<span lang="EN-US">:<o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">一<span lang="EN-US">:</span>要明确设计目标</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">接受到一个设计任务<span lang="EN-US">,</span>首先要明确其设计目标<span lang="EN-US">,</span>是普通的<span lang="EN-US">PCB</span>板、高频<span lang="EN-US">PCB</span>板、小信号处理<span lang="EN-US"><a href="http://www.pcbco.net/">PCB<span lang="EN-US"><span lang="EN-US">板</span></span></a></span>还是既有高频率又有小信号处理的<span lang="EN-US">PCB</span>板，如果是普通的<span lang="EN-US"><a href="http://www.pcbcb.com/">PCB<span lang="EN-US"><span lang="EN-US">抄</span></span><span lang="EN-US"><span lang="EN-US">板</span></span></a>,</span>只要做到布局布线合理整齐<span lang="EN-US">,</span>机械尺寸准确无误即可<span lang="EN-US">,</span>如有中负载线和长线<span lang="EN-US">,</span>就要采用一定的手段进行处理<span lang="EN-US">,</span>减轻负载<span lang="EN-US">,</span>长线要加强驱动<span lang="EN-US">,</span>重点是防止长线反射。 当板上有超过<span lang="EN-US">40MHz</span>的信号线时，就要对这些信号线进行特殊的考虑，比如线间串扰等问题。如果频率更高一些，对布线的长度就有更严格的限制，根据分布参数的网络理论，高速电路与其连线间的相互作用是决定性因素，在系统设计时不能忽略。随着门传输速度的提高，在信号线上的反对将会相应增加，相邻信号线间的串扰将成正比地增加，通常高速电路的功耗和热耗散也都很大，在做高速<span lang="EN-US">PCB</span>时应引起足够的重视。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">当板上有毫伏级甚至微伏级的微弱信号时，对这些信号线就需要特别的关照，小信号由于太微弱，非常容易受到其它强信号的干扰，屏蔽措施常常是必要的，否则将大大降低信噪比。以致于有用信号被噪声淹没，不能有效地提取出来。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">对板子的调测也要在设计阶段加以考虑，测试点的物理位置，测试点的隔离等因素不可忽略，因为有些小信号和高频信号是不能直接把探头加上去进行测量的。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">此外还要考虑其他一些相关因素，如板子层数，采用元器件的封装外形，板子的机械强度等。在做<span lang="EN-US">PCB</span>板子前，要做出对该设计的设计目标心中有数。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">二。了解所用元器件的功能对布局布线的要求</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">我们知道，有些特殊元器件在布局布线时有特殊的要求，比如<span lang="EN-US">LOTI</span>和<span lang="EN-US">APH</span>所用的模拟信号放大器，模拟信号放大器对电源要求要平稳、纹波小。模拟小信号部分要尽量远离功率器件。在<span lang="EN-US">OTI</span>板上，小信号放大部分还专门加有屏蔽罩，把杂散的电磁干扰给屏蔽掉。<span lang="EN-US">NTOI</span>板上用的<span lang="EN-US">GLINK</span>芯片采用的是<span lang="EN-US">ECL</span>工艺，功耗大发热厉害，对散热问题必须在布局时就必须进行特殊考虑，若采用自然散热，就要把<span lang="EN-US">GLINK</span>芯片放在空气流通比较顺畅的地方，而且散出来的热量还不能对其它芯片构成大的影响。如果板子上装有喇叭或其他大功率的器件，有可能对电源造成严重的污染这一点也应引起足够的重视<span lang="EN-US">. <o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">三<span lang="EN-US">. </span>元器件布局的考虑</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">元器件的布局首先要考虑的一个因素就是电性能，把连线关系密切的元器件尽量放在一起，尤其对一些高速线，布局时就要使它尽可能地短，功率信号和小信号器件要分开。在满足电路性能的前提下，还要考虑元器件摆放整齐、美观，便于测试，板子的机械尺寸，插座的位置等也需认真考虑。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">高速系统中的接地和互连线上的传输延迟时间也是在系统设计时首先要考虑的因素。信号线上的传输时间对总的系统速度影响很大，特别是对高速的<span lang="EN-US">ECL</span>电路，虽然集成电路块本身速度很高，但由于在底板上用普通的互连线（每<span lang="EN-US">30cm</span>线长约有<span lang="EN-US">2ns</span>的延迟量）带来延迟时间的增加，可使系统速度大为降低<span lang="EN-US">.</span>象移位寄存器，同步计数器这种同步工作部件最好放在同一块插件板上，因为到不同插件板上的时钟信号的传输延迟时间不相等，可能使移位寄存器产主错误，若不能放在一块板上，则在同步是关键的地方，从公共时钟源连到各插件板的时钟线的长度必须相等。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">四，对布线的考虑</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">随着<span lang="EN-US">OTNI</span>和星形光纤网的设计完成，以后会有更多的<span lang="EN-US">100MHz</span>以上的具有高速信号线的板子需要设计，这里将介绍高速线的一些基本概念。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">1</span></b><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">．传输线</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">印制电路板上的任何一条<span lang="EN-US">“</span>长<span lang="EN-US">”</span>的信号通路都可以视为一种传输线。如果该线的传输延迟时间比信号上升时间短得多，那么信号上升期间所产主的反射都将被淹没。不再呈现过冲、反冲和振铃，对现时大多数的<span lang="EN-US">MOS</span>电路来说，由于上升时间对线传输延迟时间之比大得多，所以走线可长以米计而无信号失真。而对于速度较快的逻辑电路，特别是超高速<span lang="EN-US">ECL<o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">集成电路来说，由于边沿速度的增快，若无其它措施，走线的长度必须大大缩短，以保持信号的完整性。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">有两种方法能使高速电路在相对长的线上工作而无严重的波形失真，<span lang="EN-US">TTL</span>对快速下降边沿采用肖特基二极管箝位方法，使过冲量被箝制在比地电位低一个二极管压降的电平上，这就减少了后面的反冲幅度，较慢的上升边缘允许有过冲，但它被在电平<span lang="EN-US">“H”</span>状态下电路的相对高的输出阻抗（<span lang="EN-US">50</span>～<span lang="EN-US">80Ω</span>）所衰减。此外，由于电平<span lang="EN-US">“H”</span>状态的抗扰度较大，使反冲问题并不十分突出，对<span lang="EN-US">HCT</span>系列的器件，若采用肖特基二极管箝位和串联电阻端接方法相结合，其改善的效果将会更加明显。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">当沿信号线有扇出时，在较高的位速率和较快的边沿速率下，上述介绍的<span lang="EN-US">TTL</span>整形方法显得有些不足。因为线中存在着反射波，它们在高位速率下将趋于合成，从而引起信号严重失真和抗干扰能力降低。因此，为了解决反射问题，在<span lang="EN-US">ECL</span>系统中通常使用另外一种方法：线阻抗匹配法。用这种方法能使反射受到控制，信号的完整性得到保证。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">严格他说，对于有较慢边沿速度的常规<span lang="EN-US">TTL</span>和<span lang="EN-US">CMOS</span>器件来说，传输线并不是十分需要的<span lang="EN-US">.</span>对有较快边沿速度的高速<span lang="EN-US">ECL</span>器件，传输线也不总是需要的。但是当使用传输线时，它们具有能预测连线时延和通过阻抗匹配来控制反射和振荡的优点。<span lang="EN-US">1<o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">决定是否采用传输线的基本因素有以下五个。它们是：（<span lang="EN-US">1</span>）系统信号的沿速率， （<span lang="EN-US">2</span>）连线距离 （<span lang="EN-US">3</span>）容性负载<span lang="EN-US">(</span>扇出的多少<span lang="EN-US">)</span>，（<span lang="EN-US">4</span>）电阻性负载（线的端接方式）； （<span lang="EN-US">5</span>）允许的反冲和过冲百分比（交流抗扰度的降低程度）。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">2</span></b><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">．传输线的几种类型</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">(1) </span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">同轴电缆和双绞线：它们经常用在系统与系统之间的连接。同轴电缆的特性阻抗通常有<span lang="EN-US">50Ω</span>和<span lang="EN-US">75Ω</span>，双绞线通常为<span lang="EN-US">110Ω</span>。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">2</span>）印制板上的微带线</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">微带线是一根带状导<span lang="EN-US">(</span>信号线<span lang="EN-US">)</span>．与地平面之间用一种电介质隔离开。如果线的厚度、宽度以及与地平面之间的距离是可控制的，则它的特性阻抗也是可以控制的。微带线的特性阻抗<span lang="EN-US">Z0</span>为：式中：【<span lang="EN-US">Er</span>为印制板介质材料的相对介电常数<span lang="EN-US">6</span>为介电质层的厚度<span lang="EN-US">W</span>为线的宽度<span lang="EN-US">t</span>为线的厚度单位长度微带线的传输延迟时间，仅仅取决于介电常数而与线的宽度或间隔无关。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">(3)</span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">印制板中的带状线<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">带状线是一条置于两层导电平面之间的电介质中间的铜带线。如果线的厚度和宽度、介质的介电常数以及两层导电平面间的距离是可控的，那么线的特性阻抗也是可控的，带状线的特性阻抗乙为<span lang="EN-US">:<o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">式中：<span lang="EN-US">b</span>是两块地线板间的距离<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">W</span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">为线的宽度<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">t</span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">为线的厚度<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">同样，单位长度带状线的传输延迟时间与线的宽度或间距是无关的；仅取决于所用介质的相对介电常数。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">3</span></b><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">．端接传输线</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">在一条线的接收端用一个与线特性阻抗相等的电阻端接，则称该传输线为并联端接线。它主要是为了获得最好的电性能，包括驱动分布负载而采用的。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">有时为了节省电源消耗，对端接的电阻上再串接一个<span lang="EN-US">104</span>电容形成交流端接电路，它能有效地降低直流损耗。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">在驱动器和传输线之间串接一个电阻，而线的终端不再接端接电阻，这种端接方法称之为串联端接。较长线上的过冲和振铃可用串联阻尼或串联端接技术来控制<span lang="EN-US">.</span>串联阻尼是利用一个与驱动门输出端串联的小电阻（一般为<span lang="EN-US">10</span>～<span lang="EN-US">75Ω</span>）来实现的<span lang="EN-US">.</span>这种阻尼方法适合与特性阻抗来受控制的线相联用<span lang="EN-US">(</span>如底板布线，无地平面的电路板和大多数绕接线等。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">串联端接时串联电阻的值与电路（驱动门）输出阻抗之和等于传输线的特性阻抗<span lang="EN-US">.</span>串联联端接线存在着只能在终端使用集总负载和传输延迟时间较长的缺点<span lang="EN-US">.</span>但是，这可以通过使用多余串联端接传输线的方法加以克服。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">4</span></b><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">．非端接传输线</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">如果线延迟时间比信号上升时间短得多，可以在不用串联端接或并联端接的情况下使用传输线，如果一根非端接线的双程延迟（信号在传输线上往返一次的时间）比脉冲信号的上升时间短，那么由于非端接所引起的反冲大约是逻辑摆幅的<span lang="EN-US">15</span>％。最大开路线长度近似为：<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">Lmax</span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">＜<span lang="EN-US">tr/2tpd <o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">式中：<span lang="EN-US">tr</span>为上升时间<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">tpd</span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">为单位线长的传输延迟时间<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">5</span></b><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">．几种端接方式的比较</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">并联端接线和串联端接线都各有优点，究竟用哪一种，还是两种都用，这要看设计者的爱好和系统的要求而定。并联端接线的主要优点是系统速度快和信号在线上传输完整无失真。长线上的负载既不会影响驱动长线的驱动门的传输延迟时间，又不会影响它的信号边沿速度，但将使信号沿该长线的传输延迟时间增大。在驱动大扇出时，负载可经分支短线沿线分布，而不象串联端接中那样必须把负载集总在线的终端。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">串联端接方法使电路有驱动几条平行负载线的能力，串联端接线由于容性负载所引起的延迟时间增量约比相应并联端接线的大一倍，而短线则因容性负载使边沿速度放慢和驱动门延迟时间增大，但是，串联端接线的串扰比并联端接线的要小，其主要原因是沿串联端接线传送的信号幅度仅仅是二分之一的逻辑摆幅，因而开关电流也只有并联端接的开关电流的一半，信号能量小串扰也就小。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">二<span lang="EN-US">PCB</span>板的布线技术</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">做<span lang="EN-US">PCB</span>时是选用双面板还是多层板，要看最高工作频率和电路系统的复杂程度以及对组装密度的要求来决定。在时钟频率超过<span lang="EN-US">200MHZ</span>时最好选用多层板。如果工作频率超过<span lang="EN-US">350MHz</span>，最好选用以聚四氟乙烯作为介质层的印制电路板，因为它的高频衰耗要小些，寄生电容要小些，传输速度要快些，还由于<span lang="EN-US">Z0</span>较大而省功耗，对印制电路板的走线有如下原则要求<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">1</span>）所有平行信号线之间要尽量留有较大的间隔，以减少串扰。如果有两条相距较近的信号线，最好在两线之间走一条接地线，这样可以起到屏蔽作用。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">(2) </span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">设计信号传输线时要避免急拐弯，以防传输线特性阻抗的突变而产生反射，要尽量设计成具有一定尺寸的均匀的圆弧线。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">印制线的宽度可根据上述微带线和带状线的特性阻抗计算公式计算，印制电路板上的微带线的特性阻抗一般在<span lang="EN-US">50</span>～<span lang="EN-US">120Ω</span>之间。要想得到大的特性阻抗，线宽必须做得很窄。但很细的线条又不容易制作。综合各种因素考虑，一般选择<span lang="EN-US">68Ω</span>左右的阻抗值比较合适，因为选择<span lang="EN-US">68Ω</span>的特性阻抗，可以在延迟时间和功耗之间达到最佳平衡。一条<span lang="EN-US">50Ω</span>的传输线将消耗更多的功率；较大的阻抗固然可以使消耗功率减少，但会使传输延迟时间憎大。由于负线电容会造成传输延迟时间的增大和特性阻抗的降低。但特性阻抗很低的线段单位长度的本征电容比较大，所以传输延迟时间及特性阻抗受负载电容的影响较小。具有适当端接的传输线的一个重要特征是，分枝短线对线延迟时间应没有什么影响。当<span lang="EN-US">Z0</span>为<span lang="EN-US">50Ω</span>时。分枝短线的长度必须限制在<span lang="EN-US">2</span>．<span lang="EN-US">5cm</span>以内．以免出现很大的振铃。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">4</span>）对于双面板（或六层板中走四层线）．电路板两面的线要互相垂直，以防止互相感应产主串扰。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">5</span>）印制板上若装有大电流器件，如继电器、指示灯、喇叭等，它们的地线最好要分开单独走，以减少地线上的噪声，这些大电流器件的地线应连到插件板和背板上的一个独立的地总线上去，而且这些独立的地线还应该与整个系统的接地点相连接。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">6</span>）如果板上有小信号放大器，则放大前的弱信号线要远离强信号线，而且走线要尽可能地短，如有可能还要用地线对其进行屏蔽。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: center" align="center"><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"><o:p>&nbsp;</o:p></span></p>http://www.sichinamag.com/blog/pcbsu/31607/message.aspx 检测与测量Tue, 02 Sep 2008 09:39:29 GMThttp://www.sichinamag.com/blog/pcbsu/31606/message.aspx<p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: center" align="center"><b style="mso-bidi-font-weight: normal"><span style="FONT-SIZE: 12pt; COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">如何在</span></b><b style="mso-bidi-font-weight: normal"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; FONT-FAMILY: Arial"><a href="http://www.ldpcb.com/">PCB<span lang="EN-US" style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial"><span lang="EN-US">设计</span></span></a></span></b><b style="mso-bidi-font-weight: normal"><span style="FONT-SIZE: 12pt; COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial">中加强防干扰能力</span></b><b style="mso-bidi-font-weight: normal"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; FONT-FAMILY: Arial"><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></span></b></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">印制电路板（<span lang="EN-US">PCB</span>）是电子产品中电路元件和器件的支撑件。它提供电路元件和器件之间的电气连接。随着电子技术的飞速发展，<span lang="EN-US"><a href="http://www.pcbco.net/">PCB</a></span>的密度越来越高。<span lang="EN-US">PCB</span>设计的好坏对抗干扰能力影响很大。实践证明，即使电路原理图设计正确，印制电路板设计不当，也会对电子产品的可靠性产生不利影响。例如，如果印制板两条细平行线靠得很近，则会形成信号波形的延迟，在传输线的终端形成反射噪声。因此，在设计印制电路板的时候，应注意采用正确的方法，遵守<span lang="EN-US">PCB</span>设计的一般原则，并应符合抗干扰设计的要求。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">一、 </span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><a href="http://www.x5dj.com/pcbpcbsxl/"><b><span style="COLOR: #0059d1; TEXT-DECORATION: none; text-underline: none">PCB</span></b><b><span lang="EN-US" style="COLOR: #0059d1; TEXT-DECORATION: none; text-underline: none"><span lang="EN-US">设计</span></span></b></a></span><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">的一般原则</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">要使电子电路获得最佳性能，元器件的布局及导线的布设是很重要的。为了设计质量好、造价低的<span lang="EN-US">PCB</span>，应遵循以下的一般性原则：<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">布局</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">首先，要考虑<span lang="EN-US">PCB</span>尺寸大小。<span lang="EN-US">PCB</span>尺寸过大时，印制线条长，阻抗增加，抗噪声能力下降，成本也增加；过小，则散热不好，且邻近线条易受干扰。在确定<span lang="EN-US">PCB</span>尺寸后，再确定特殊元件的位置。最后，根据电路的功能单元，对电路的全部元器件进行布局。<span lang="EN-US"><br></span>在确定特殊元件的位置时要遵守以下原则：<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">1</span>）尽可能缩短高频元器件之间的连线，设法减少它们的分布参数和相互间的电磁干扰。易受干扰的元器件不能相互挨得太近，输入和输出元件应尽量远离。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">2</span>）某些元器件或导线之间可能有较高的电位差，应加大它们之间的距离，以免放电引出意外短路。带高电压的元器件应尽量布置在调试时手不易触及的地方。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">3</span>）重量超过<span lang="EN-US">15g</span>的元器件，应当用支架加以固定，然后焊接。那些又大又重、发热量多的元器件，不宜装在印制板上，而应装在整机的机箱底板上，且应考虑散热问题。热敏元件应远离发热元件。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">4</span>）对于电位器、可调电感线圈、可变电容器、微动开关等可调元件的布局应考虑整机的结构要求。若是机内调节，应放在印制板上方便调节的地方；若是机外调节，其位置要与调节旋钮在机箱面板上的位置相适应。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">5</span>）应留出印制板定位孔及固定支架所占用的位置。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><a href="http://www.pcbres.com/upimg/userup/0804/121G222AV.jpg" target=_blank><span style="COLOR: #0059d1; TEXT-DECORATION: none; text-underline: none"><?xml:namespace prefix = v ns = "urn:schemas-microsoft-com:vml" /><v:shapetype id=_x0000_t75 stroked="f" filled="f" path="m@4@5l@4@11@9@11@9@5xe" o:preferrelative="t" o:spt="75" coordsize="21600,21600"><v:stroke joinstyle="miter"></v:stroke><v:formulas><v:f eqn="if lineDrawn pixelLineWidth 0"></v:f><v:f eqn="sum @0 1 0"></v:f><v:f eqn="sum 0 0 @1"></v:f><v:f eqn="prod @2 1 2"></v:f><v:f eqn="prod @3 21600 pixelWidth"></v:f><v:f eqn="prod @3 21600 pixelHeight"></v:f><v:f eqn="sum @0 0 1"></v:f><v:f eqn="prod @6 1 2"></v:f><v:f eqn="prod @7 21600 pixelWidth"></v:f><v:f eqn="sum @8 21600 0"></v:f><v:f eqn="prod @7 21600 pixelHeight"></v:f><v:f eqn="sum @10 21600 0"></v:f></v:formulas><v:path o:connecttype="rect" gradientshapeok="t" o:extrusionok="f"></v:path><o:lock aspectratio="t" v:ext="edit"></o:lock></v:shapetype><v:shape id=_x0000_i1025 style="WIDTH: 172.5pt; HEIGHT: 133.5pt" o:button="t" target="_blank" href="http://www.pcbres.com/upimg/userup/0804/121G222AV.jpg" alt="如何加强PCB的防干扰能力" type="#_x0000_t75"><v:imagedata o:href="http://www.pcbres.com/upimg/userup/0804/121G222AV.jpg" src="file:///C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\msohtml1\01\clip_image001.jpg"></v:imagedata></v:shape></span></a>&nbsp;<o:p></o:p></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">根据电路的功能单元。对电路的全部元器件进行</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><a href="http://hexun.com/pcbsxl01"><b><span style="COLOR: #0059d1; TEXT-DECORATION: none; text-underline: none">PCB</span></b><b><span lang="EN-US" style="COLOR: #0059d1; TEXT-DECORATION: none; text-underline: none"><span lang="EN-US">布局</span></span></b></a></span><b><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">时，要符合以下原则：</span></b><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">1</span>）按照电路的流程安排各个功能电路单元的位置，使布局便于信号流通，并使信号尽可能保持一致的方向。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">2</span>）以每个功能电路的核心元件为中心，围绕它来进行布局。元器件应均匀、整齐、紧凑地排列在<span lang="EN-US">PCB</span>上。尽量减少和缩短各元器件之间的引线和连接。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">3</span>）在高频下工作的电路，要考虑元器件之间的分布参数。一般电路应尽可能使元器件平行排列。这样，不但美观，而且装焊容易，易于批量生产。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 12pt 0cm; TEXT-INDENT: 24pt; TEXT-ALIGN: left; mso-pagination: widow-orphan" align="left"><span lang="EN-US" style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt"><br></span><span style="FONT-SIZE: 9pt; COLOR: black; FONT-FAMILY: 宋体; mso-bidi-font-family: Arial; mso-font-kerning: 0pt">（<span lang="EN-US">4</span>）位于电路板边缘的元器件，离电路板边缘一般不小于<span lang="EN-US">2mm</span>。电路板的最佳形状为矩形。长宽双为<span lang="EN-US">3:2</span>或<span lang="EN-US">4:3</span>。电路板面尺寸大于<span lang="EN-US">200×150mm</span>时，应考虑电路板所受的机械强度。<span lang="EN-US"><o:p></o:p></span></span></p> <p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: center" align="center"><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体"><o:p>&nbsp;</o:p></span></p>http://www.sichinamag.com/blog/pcbsu/31606/message.aspx IC设计与软件