共模信号和差模信号

共模信号和差模信号 了解共模和差模信号之间的差别，对正确理解脉冲磁路和工作模块之间的关系是至关重要的。变压器、共模扼流圈和自耦变压器的端接法，对在局域网(LAN)和通信接口电路中减小共模干扰起关键作用。共模噪音在用无屏蔽对绞电缆线的通信系统中，是引起射频干扰的主要因素，所以了解共模噪音将有利于更好地了解我们关心的磁性界面的电磁兼容论点。本文的主要目的是阐述差模和共模信号的关键特性和共模扼流圈、自耦变压器端接法主要用途，以及为什么共模信号在无屏蔽对绞电缆线上会引起噪音发射。在介绍这些信号特点的同时，还介绍了抑制一般噪音常用的方法。 图1差模信号 图2差模信号的波形图 2差模和共模信号 我们研究简单的两线电缆，在它的终端接有负载阻抗。每一线对地的电压用符号V1和V2来表示。差模信号分量是VDIFF，共模信号分量是VCOM，电缆和地之间存在的寄生电容是Cp。其电路如图1所示，其波形如图2所示。 poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County, 2(1差模信号 纯差模信号是:V1=,V2(1) 大小相等，相位差是180? VDIFF=V1,V2(2) 因为V1和V2对地是对称的，所以地线上没有电流流过。所有的差模电流(IDIFF)全流过负载。 在以电缆传输信号时，差模信号是作为携带信息“想要”的信号。局域网(LAN)和通信中应用的无线收发机的结构中安装的都是差模器件。两个电压(V1，V2)瞬时值之和总是等于零。 2(2共模信号 纯共模信号是: V1=V2=VCOM(3) 大小相等，相位差为0? V3=0(4) 共模信号的电路如图3所示，其波形如图4所示。 因为在负载两端没有电位差，所以没有电流流过负载。所有的共模电流都通过电缆和地之间的寄生电容流向地线。在以电缆传输信号时，因为共模信号不携带信息，所以它是“不想要”的信号。 图3共模信号 poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County, 图4共模信号的波形图 图5无屏蔽对绞线系统中的差模信号 图6无屏蔽对绞线系统中的共模信号 两个电压瞬时值之和(V1，V2)不等于零。相对于地而言，每一电缆上都有变化的电位差。这变化的电位差就会从电缆上发射电磁波。 3差模和共模信号及其在无屏蔽对绞线中的EMC 在对绞电缆线中的每一根导线是以双螺旋形结构相互缠绕着。流过每根导线的电流所产生的磁场受螺旋形的制约。流过对绞线中每一根导线的电流方向，决定每对导线发射噪音的程度。在每对导线上流过差模和共模电流所引起的发射程度是不同的，差模电流引起的噪音发射是较小的，所以噪音主要是由共模电流决定。 3(1对绞线中的差模信号 对纯差模信号而言，它在每一根导线上的电流是以相反方向在一对导线上传送。如果这一对导线是均匀的缠绕，这些相反的电流就会产生大小相等，反向极化的磁场，使它的输出互相抵消。在无屏蔽对绞线系统中的差模信号如图5所示。 在无屏蔽对绞线中，不含噪音的差模信号不产生射频干扰。 poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County, 3(2对绞线中的共模信号 共模电流ICOM在两根导线上以相同方向流动，并经过寄生电容Cp到地返回。在这种情况下，电流产生大小相等极性相同的磁场，它们的输出不能相互抵消。如图6所示，共模电流在对绞线的表面产生一个电磁场，它的作用正如天线一样。 在无屏蔽对绞线中，共模信号产生射频干扰。 3(3电缆线上产生的共模、差模噪音及其EMC 电子设备中电缆线上的噪音有从电源电缆和信号电缆上产生的辐射噪音和传导噪音两大类。这两大类中又分为共模噪音和差模噪音两种[1]。 差模传导噪音是电子设备内部噪音电压产生的与信号电流或电源电流相同路径的噪音电流，如图7所示。减小这种噪音的方法是在信号线和电源线上串联差模扼流圈、并联电容或用电容和电感组成低通滤波器，来减小高频的噪音，如图8所示。 差模辐射噪音是图7电缆中的信号电流环路所产生的辐射。这种噪音产生的电场强度与电缆到观测点的距离成反比，与频率的平方成正比，与电流和电流环路的面积成正比。因此，减小这种辐射的方法是在信号输入端加LC低通滤波器阻止噪音电流流进电缆;使用屏蔽电缆或扁平电缆，在相邻的导线中传输回流电流和信号电流，使环路面积减小。 共模传导噪音是在设备内噪音电压的驱动下，经过大地与设备之间的寄生电容，在大地与电缆之间流动的噪音电流产生的，如图9所示。减小共模传导噪音的方法是在信号线或电源线中串联共模扼流圈、在地与导线之间并联电容器、组成LC滤波器进行滤波，滤去共模传导噪声。其电路如图10所示。共模扼流圈是将电源线的零线和火线(或回流线和信号线)同方向绕在铁氧体磁芯上构成的，它对线间流动的差模信号电流和电源电流阻抗很小，而对两根导线与地之间流过的共模电流阻抗则很大。 poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County, 图7差模噪声 图8差模噪声的抑制 图9共模噪声 图10共模噪声的抑制 共模辐射噪音是由于电缆端口上有共模电压，在其驱动下，从大地到电缆之间有共模电流流动而产生的。辐射的电场强度与电缆到观测点的距离成反比，(当电缆长度比电流的波长短时)与频率和电缆的长度成正比。减小这种辐射的方法有:通过在线路板上使用地线面来降低地线阻抗，在电缆的端口处使用LC低通滤波器或共模扼流圈。另外，尽量缩短电缆的长度和使用屏蔽电缆也能减小辐射。 poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County, 在有些电路中也可接入图11所示的抗干扰变压器来防止差模和共模噪音。 4变压器与噪音传导 理想变压器理论上是完美的电路元件，它能用完美的磁耦合在初级和次级绕组之间传送电能。理想变压器只能传送交变的差模电流。它不能传送共模电流，因为共模电流在变压器绕组两端的电位差为零，不能在变压器绕组上产生磁场。 实际变压器初级和次级绕组之间有一个很小但不等于零的耦合电容CWW，见图12。这个电容是绕组之间存在非电介质和物理间隙所产生的。增加绕组之间的空隙和用低介电常数的材料填满绕组之间的空间就能减小绕组之间电容的数值。 电容Cww为共模电流提供一条穿过变压器的通道，其阻抗是由电容量的大小和信号频率来决定的。 5共模扼流圈 对于理想的单磁芯、双绕组的共模扼流圈，将不考虑在实际扼流圈中或多或少存在的杂散阻抗(Cww,DCR,Cp等)的影响。这样的假设是合理的，因为一个好的扼流圈设计，它的杂散阻抗和电路的源阻抗、负载阻抗相比是可以忽略的。 5(1理想共模扼流圈对差模信号的效应 差模电流以相反的方向流过共模扼流圈的绕阻，建立大小相等，极性相反的磁场，它能使输出相互抵消，见图13。这就使共模扼流圈对差模信号的阻抗为零。差模信号能不受阻地通过共模扼流圈。 5(2理想共模扼流圈对共模信号的效应 共模电流以相同的方向流过共模扼流圈绕组的每一边，见图14，它建立大小相等相位相同的相加磁场。这一结果就使共模扼流圈对共模信号呈现高阻抗，使通过共模扼流圈的共模电流大大地减弱。实际减弱量(或共模抑制量)取决于共模扼流圈阻抗和负载阻抗大小之比。 poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County, 图11抗干扰变压器 图12变压器初级和次级绕组之间的耦合电容 图13理想共模扼流圈中的差模信号 图14理想共模扼流圈中的共模信号 图15理想自耦变压器中的差模信号 poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County, 图16理想自耦变压器中的共模信号 6有中心抽头的自耦变压器 自耦变压器是以定向电流传递方式实现能量传输的。对于理想的自耦变压器[2]，不考虑实际或多或少存在的杂散阻抗(Cww,DCR,Cp等)的影响。这样的假设是合理的，因为一个好的自耦变压器设计，它的杂散阻抗和电路的源阻抗、负载阻抗相比是可以忽略的。 6(1理想自耦变压器对差模信号的效应 从差模信号看，有中心抽头的自耦变压器是两个在相位上相同的对分绕组，见图15。这就意味差模电流在其中所形成的磁场，会使其对差模电流呈现高阻抗。相当于对差模信号并联了一个高阻值的阻抗，它对差模信号的大小没有影响。 6(2理想自耦变压器对共模信号的效应 从共模信号看，有中心抽头的自耦变压器是两个在相位上相反的对分绕组，见图16。这就意味共模电流在其中会形成大小相等相位相反的磁场，这一磁场会使共模电流的输出互相抵消。对共模信号呈现零阻抗效应，使共模信号直接短路到地。 7减小电磁干扰的一些常用方法 通常都是在电路设计、印制板布线上想办法来减小电磁干扰或在机箱上增加屏蔽、采用有中心线的共模扼流圈等方法来减小电磁干扰。 7(1屏蔽 用金属材料将机箱内部产生的噪音封闭起来的方法称为屏蔽。屏蔽对防止外部噪音进入机箱也是同样有效的。电场屏蔽和磁场屏蔽的方法是不同的。 poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County, 电场屏蔽是用导体将噪音源包围起来，然后接地，就能达到屏蔽的目的。由于导体表面的反射损耗很大，因此很薄的材料(铝箔、铜箔)也有很好的屏蔽效果。另外，机箱上即使有缝隙，也不会产生太大的影响。 磁场屏蔽主要用来屏蔽低频磁场的干扰，这种干扰是由交流电流或直流电流产生的。例如，感应炼钢炉中有数万安培的电流通过，在炉周围产生很强的磁场，这个强磁场会使控制系统中的磁敏器件失灵。最常见的磁敏器件是彩色CRT显示器，在磁场的作用下，显示器屏幕上的图象颜色会失真，图象会产生抖动，导致显示质量严重降低，甚至无法使用。低频磁场往往随距离的增加而衰减很快，因此在很多场合，将磁敏器件远离磁场源是减小磁场干扰的十分有效的。但当空间的限制而无法采取这个方法时，屏蔽也是一个十分有效的措施。要注意的是，低频磁场屏蔽与射频磁场屏蔽是完全不同的，射频磁场的屏蔽使用导电率高的材料如铍铜复合材料、银、锡或铝等材料，把它完全封闭起来，就可以了。但这些材料对低频磁场没有任何屏蔽作用。只有高导磁率的铁磁合金才能屏蔽直流磁场或低频磁场。 根据电磁屏蔽的基本原理，低频磁场由于其频率低，吸收损耗很小，趋肤效应很小，并且由于其波阻抗很低，反射损耗也很小，因此单纯靠反射和吸收很难获得需要的屏蔽效果。对这种低频磁场，要通过使用高导磁率材料为磁场提供一条磁阻很低的旁路来实现屏蔽，这样空间的磁场便会集中在屏蔽材料中，从而使磁敏器件免受磁场干扰。 高导磁率材料在机械的冲击下会极大地损失磁性，导致屏蔽效能下降。因此，屏蔽体在经过机械加工(如折弯、焊接、敲击、钻孔等)后，必须经过热处理以恢复磁性。热处理要在特定条件下进行，一般要在干燥氢气炉中以一定的速率加热到1177?，保持4个小时，然后以一定的速率降低到室温。 poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County, 在对拼连接处进行焊接时，要使用屏蔽材料母料做焊接填充料，这样可以保证焊缝处的高导磁率。如果屏蔽效能要求较低，也可以采用铆接或点焊的方式固定，但要注意拼接处的屏蔽材料要有一定的重叠，以保证磁路上较小的磁阻。 图17有中心线的共模扼流圈 图18有中心线的共模扼流圈的典型响应曲线 当需要屏蔽的磁场很强时，仅用单层屏蔽材料，达不到屏蔽要求。这时，一种方法是增加材料的厚度。但更有效的方法是使用组合屏蔽，将一个屏蔽体放在另一个屏蔽体内，它们之间留有气隙。气隙内可以填充任何非导磁材料(如铝)做支撑。组合屏蔽的屏蔽效果比单个屏蔽体高得多，因此组合屏蔽能够将磁场衰减到很低的程度。 7(2电路设计 由于时钟频率越高，高频能量的发射越强，因此在数字电路中不要使用过高的时钟频率。印制板上的总线、较大的环路面积和较长的导线都是强辐射源，因此，除非必要，要尽量避免这些情况的出现。使用大规模集成电路能够大幅度减少印制板上的走线，从而减小辐射。在选用集成电路时，也有些问题需要注意。例如，高速肖特基电路由于脉冲上升时间很短，因poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County, 此会在很高的频率范围内产生发射。在功能允许的条件下，尽量使用标准型电路。电路设计时要最大限度地保持数字线和信号线分离。信号通道必须远离输入输出线以防止数字线上开关噪音辐射到信号线上。 7(3印制板的设计 在印制板上合适的放置元器件与合理的安排印制板走线是很关键的。有些元器件，特别是磁性元件(如滤波器)在一个方向比其它方向可能有更大的磁场。元器件相互之间成90?放置，磁场相互抵消并减小噪音辐射。开关器件远离磁性元件也能减小噪音辐射。印制板上的走线也是主要的辐射源。走线产生辐射主要是由于逻辑电路中电流的突变，在走线的电感上产生感应电压，这个电压会产生较强的噪音辐射。另外，由于走线起着发射天线的作用，因此走线的长度越长，辐射的噪音越多。短的走线比长的走线辐射少。粗的走线比细的走线噪音辐射少。所以使走线尽可能地短，从而把走线的自感减到最小是很必要的。 7(4采用有中心线的共模扼流圈 减少和改善噪音的另一种方法，特别是对高频段，是在传输频道上用有中心线的共模扼流圈，如图17所示。 共模扼流圈的耦合电容对中心线的每一边是对称的。变压器的次级具有分路，这分路有助于变压器的次级绕组的分布电容更好地控制传输频道上的返回损耗。它还可以在高频段提供一阻尼的下凹，其频率范围出现在(700,900)MHz之间，这个范围也可以进行控制，典型的响应曲线见图18。 poverty alleviation, making stable poverty of village and exit in a timely manner, should support poverty alleviation into, from the ... The stability of families, not simply one off, not only to "help a horse", and "giving a lift" to prevent poverty and returning again. (D) to co-ordinate the configuration resource for poverty alleviation. One hand to work actively towards a superior policy. Central work Conference of poverty-alleviation, Central Government of General transfer payments, various types of special transfer payments involving the people's livelihood, in order to further to poor areas. National Revolutionary development seminars presented "five closely around the", developed to support development and construction of old revolutionary views. Prime Minister Li keqiang on the CPPCC was specifically proposed in the Government work report: "national waste management policies and the people's livelihood projects to impoverished areas." Meanwhile, provinces and cities will also be supporting the introduction of appropriate policies. These policies is very large, the ... ... For counties not only opportunities for poverty eradication, it is catching up, promote the development of opportunities in the surrounding area. Departments at all levels must firmly grasp this golden opportunity, let these opportunities become crucial for poverty eradication not only a powerful lever, also became ... ... Powerful breakthrough to overall development, with overtaking. Other integration-related funds. At the meeting, "two offices" introduced the integration of agriculture-related projects funds giving priority to poor implementation of village-poor tilt, clear integration of the 4 major categories of funds and use of the process. The involved departments, under the unified command of the leading group of poverty alleviation and development in the County,