1. 0 ohm resistor
The resistance of 0 ohms is commonly seen in circuit design, and everyone is often confused: since it is a resistance of 0 ohms, it is a wire, why should it be installed? Are there any such resistors on the market? In fact, a 0 ohm resistor is quite useful. There are probably the following functions, the most important and frequently used functions are:
Key introduction: single-point grounding of analog ground and digital ground
As long as it is the ground, it will eventually be received together, and then enter the earth. If they are not connected together, they are "floating ground", there is a voltage difference, and it is easy to accumulate charges and cause static electricity. The ground is referenced to 0 potential, and all voltages are derived from the reference ground. The standard of the ground should be the same, so the various grounds should be shorted together. The earth is believed to be the ultimate ground reference point, capable of absorbing all electrical charges, remaining stable at all times. Although some boards are not connected to the ground, the power plant is connected to the ground, and the power on the board will eventually return to the power plant into the ground. If the analog ground and the digital ground are directly connected in a large area, it will cause mutual interference. There are four ways to solve this problem:
① Connect with magnetic beads;
② Connect with capacitor;
③ Connect with inductance;
④ Connect with 0 ohm resistor.
the difference:
① The equivalent circuit of the magnetic bead is equivalent to a band-stop wave limiter, which can only significantly suppress the noise of a certain frequency point. The frequency of the noise point needs to be estimated in advance in order to select the appropriate model. Magnetic beads are not suitable for situations where the frequency is uncertain or unpredictable.
② The capacitor blocks the direct traffic, causing floating.
③ The inductor is large in size, has many stray parameters, and is unstable.
④ The 0 ohm resistor is equivalent to a very narrow current path, which can effectively limit the loop current and suppress the noise. Resistors have a damping effect in all frequency bands (0 ohm resistors also have impedance ) , which is stronger than magnetic beads.
Other uses of 0 ohm resistors
① There is no function in the circuit, but it is only on the PCB for debugging convenience or compatible design.
② It can be used as a jumper. If a certain line is not used, just do not paste the resistor directly (does not affect the appearance).
③ When the parameters of the matching circuit are uncertain, use 0 ohm instead. When debugging, determine the parameters and replace them with components with specific values.
④ When measuring the current consumption of a certain part of the circuit, you can remove the 0ohm resistor and connect an ammeter, which is convenient for measuring the current consumption.
⑤ When wiring, if the wiring cannot be done, you can also add a 0 ohm resistor.
⑥ Act as an inductor or capacitor under high frequency signals. ( Related to external circuit characteristics) Inductors are mainly used to solve EMC problems . Such as ground and ground, between power supply and IC Pin
⑦ Single-point grounding ( meaning that the protective grounding, working grounding, and DC grounding are separated from each other on the equipment , and each becomes an independent system.)
⑧ Fuse function
⑨ Used for current loop when connected across
When the electrical ground plane is divided, the shortest return path of the signal is broken. At this time, the signal loop has to be detoured, forming a large loop area, and the influence of the electric field and the magnetic field becomes stronger, and it is easy to be disturbed / disturbed. Connecting a 0 ohm resistor across the partition can provide a short return path and reduce interference.
⑩ Configuration circuit
一般，产品上不要出现跳线和拨码开关。有时用户会乱动设置，易引起误会，为了减少维护费用，应用0欧电阻代替跳线等焊在板子上。空置跳线在高频时相当于天线，用贴片电阻效果好。
⑾ 其他用途
布线时跨线、调试/测试用、临时取代其他贴片器件、作为温度补偿器件，更多时候是出于EMC对策的需要。另外，0欧姆电阻比过孔的寄生电感小，而且过孔还会影响地平面（因为要挖孔），还有就是不同尺寸0欧电阻允许通过电流不同，一般0603的1A，0805 的2A，所以不同电流会选用不同尺寸的。还有就是为磁珠、电感等预留位置时，得根据磁珠、电感的大小还做封装，所以0603、0805等不同尺寸的都有了。
附：1欧姆电阻的作用
1欧姆电阻在电路中经常是用来测试的,比如,需要测一个电路中的电流时,我们可以在该电路中串一个1欧姆电阻,测量其两端的电压即是该电路的电流(I=U/R,因为R=1,所以测出的电压值即是电流值)。
二、磁珠：
磁珠专用于抑制信信号线、电源线上的高频噪声和尖峰干扰，还具有吸收静电脉冲的能力。磁珠是用来吸收超高频信号，象一些RF电路，PLL，振荡电路，含超高频存储器电路（DDR，SDRAM，RAMBUS等）都需要在电源输入部分加磁珠，而电感是一种蓄能元件，用在LC振荡电路，中低频的滤波电路等，其应用频率范围很少超过50MHZ。 磁珠有很高的电阻率和磁导率，等效于电阻和电感串联，但电阻值和电感值都随频率变化。
磁珠的功能：主要是消除存在于传输线结构（电路）中的RF噪声，RF能量是叠加在直流传输电平上的交流正弦波成分，直流成分是需要的有用信号，而射频RF能量却是无用的电磁干扰沿着线路传输和辐射（EMI）。要消除这些不需要的信号能量，使用片式磁珠扮演高频电阻的角色（衰减器），该器件允许直流信号通过，而滤除交流信号。通常高频信号为30MHz以上，然而，低频信号也会受到片式磁珠的影响。
磁珠有很高的电阻率和磁导率，它等效于电阻和电感串联，但电阻值和电感值都随频率变化。 它比普通的电感有更好的高频滤波特性，在高频时呈现阻性，所以能在相当宽的频率范围内保持较高的阻抗，从而提高调频滤波效果。
作为电源滤波，可以使用电感。磁珠的电路符号就是电感但是型号上可以看出使用的是磁珠在电路功能上，磁珠和电感是原理相同的，只是频率特性不同罢了。
注：磁珠的单位是欧姆，指100MHz时的阻抗，如一般标为120 Ohm@100MHz，而不是亨利，这一点要特别注意。
三、电感
电感是闭合回路的一种属性。当线圈通过电流后，在线圈中形成磁场感应，感应磁场又会产生感应电流来抵制通过线圈中的电流。这种电流与线圈的相互作用关系称为电的感抗，也就是电感，单位是“亨利（H）”。
注：关于电感只在此简要介绍，此内容会在后文中体现。
磁珠和电感的区别
电感是储能元件，而磁珠是能量转换（消耗）器件。电感多用于电源滤波回路，侧重于抑止传导性干扰；磁珠多用于信号回路，主要用于EMI方面。磁珠用来吸收超高频信号，象一些RF电路，PLL，振荡电路，含超高频存储器电路（DDR，SDRAM，RAMBUS等）都需要在电源输入部分加磁珠，而电感是一种储能元件，用在LC振荡电路、中低频的滤波电路等，其应用频率范围很少超过50MHz。在电路功能上，磁珠和电感是原理相同的，只是频率特性不同罢了。
转自：http://www.cnblogs.com/tdyizhen1314/archive/2012/10/11/2720408.html