The Study of electronic circuit noise
Abstract: with the rapid development of electronic technology, all kinds of electronic equipment, or system to widely appeared in people's lives. Around the equipment, or system at run time to launch the electromagnetic energy, produces interference to other electronic equipment, serious when can cause certain electronic noise sources and its suppression methods are discussed. By the basic knowledge of electronic noise, electronic devices, the internal noise of electronic circuit, the noise calculation of electronic noise sources in the circuit are discussed and the effective method to
suppress noise.
Keywords: internal noise sources, suppressed
目录
1.引言 ........................................................................................................................................................... 1
2.噪声的定义及其特性 .............................................................................................................................. 1
3.几种常见的电子噪声 ............................................................................................................................... 1
3.1电阻热噪声 ................................................................................................................................... 1
3.2晶体管及其噪声 ........................................................................................................................... 3
3.3低频噪声和电路板上电磁原件的干扰 ....................................................................................... 6
4噪声的量度 ............................................................................................................................................... 7
4.1信噪比 ............................................................................................................................................ 7
4.2噪声系数 ................................................................................................................................ 8
4.3噪声温度 ................................................................................................................................ 8
4.4分贝单位 ................................................................................................................................ 9
5噪声干扰的路径 ....................................................................................................................................... 9
5.1噪声的耦合方式 ........................................................................................................................... 9
5.2公共阻抗耦合 .............................................................................................................................. 10
5.3直接耦合 ...................................................................................................................................... 10
5.4电容耦合 ...................................................................................................................................... 11
5.5电磁感应耦合 .............................................................................................................................. 12
5.6漏电耦合 ...................................................................................................................................... 13
5.7辐射耦合 ...................................................................................................................................... 13
6电子产品噪声的常规检测方法 ............................................................................................................. 14
7噪声干扰的克服方法 ............................................................................................................................. 15
7.1 合理的选择器件 ......................................................................................................................... 16
7.2 采用优质的电源 ......................................................................................................................... 17
7.3 对电路合理的布局 ..................................................................................................................... 18
7.4抑制和减少输入端偏置电路的噪声 .......................................................................................... 18
7.5 通过对路径的控制来克服噪声干扰 ......................................................................................... 19
7.5.1 选择合理的接地点 .......................................................................................................... 19
7.5.2 加入校正电路 .................................................................................................................. 20
7.5.3根据不同的工作频段、参数选择适当的放大电路: ...................................................... 21
7.5.4合理选取级间藕合也可以抑制噪声 ............................................................................... 21
7.6通过处理接收方来减小噪声干扰 .............................................................................................. 21
7.6.1 屏蔽接收端 ...................................................................................................................... 21
7.6.2 静电屏蔽 .......................................................................................................................... 21
7.6.3 电磁屏蔽 .......................................................................................................................... 22
7.6.4 加入滤波电容和补偿电路 .............................................................................................. 23
7.7 其他克服噪声干扰的方法 ......................................................................................................... 25
7.7.1 对称消除噪声法 .............................................................................................................. 25
7.7.2 滤波方法 .......................................................................................................................... 25
1.引言
随着人们生活水平的提高，各种家电，手机、电视、电脑等高精度电子产品已经走进了普通百姓的家庭，成为人们生活不可缺的电子产品。而电子电路的噪声抑制也应经成为一个必须解决的问题，因为电子噪声造成的危害是无法估量的，轻则使电子设备或系统的工作性能等级下降，重则使人们的名财产受到严重威胁。因此电子电路中的噪声已经成为一个亟待解决的问题。
2.噪声的定义及其特性
所谓噪声，是指出有用信号以外的一切不需要的信号以及各种电磁骚动的总成。噪声与干扰是同义词，没有本质区别，而习惯上将外部来的称为干扰，内部产生的称为噪声。从原理上说，任何电子线路都有噪声，但一般情况下电子电路中的噪声强度都很弱，因此它的影响主要出现在有用信号比较弱的场合，如接收机的前级电路或多级高效增益的音频放大、视频放大器中。在这些电路中，本身较弱的噪声及信号通过多级放大后可以对系统产生不可估量的影响，因此对其噪声的抑制是必要的。
3.几种常见的电子噪声
3.1电阻热噪声
一个导体或者电阻中有着大量的自由电子，由于温度的原因，在这其中的电子都会做不规则的运动，温度越高，自由电子的运动就越剧烈。就一个电子来看，它的一次运动过程就会在电阻两端产生起伏的电压。从一段时间看，进出电阻的电子量是一样的，因而电阻两端的平均电压应为零；但就某一瞬间看，电阻两端的电子量是不可能一致的，因而电阻两端的电势e的大小是随机变化的。图3-1为电阻热噪声的一段电压波形波形：