We often see 0 ohm resistors in the circuit. For newcomers, it is often confusing: since it is a 0 ohm resistor, it is a wire. Why should it be installed? Is there such a resistor sold in the market? In fact, the resistance of 0 ohms is quite useful.
Zero ohm resistor, also known as jumper resistor, is a special purpose resistor. The 0 ohm resistor is not really zero resistance (that is the superconductor dry thing), just because of the resistance, it is also a regular paste. The chip resistor has the same error accuracy as this indicator.
The following summarizes a series of usages of zero ohm resistors:
1. There is no function in the circuit, just for the convenience of debugging or compatible design on the PCB.
2. Can be used for jumpers, if a certain line is not used, you can directly not attach the resistor (does not affect the appearance)
3. When the matching circuit parameters are uncertain, replace it with 0 ohms. When the actual debugging is performed, determine the parameters and replace them with specific numerical components.
4. When you want to measure the current consumption of a certain part of the circuit, you can remove the 0ohm resistor and connect the ammeter to facilitate the current consumption.
5. In the wiring, if the actual cloth can not pass, you can also add a 0 ohm resistor
6. Act as an inductor or capacitor under high frequency signals. (related to external circuit characteristics) Inductive use, mainly to solve EMC problems. Such as ground and ground, power and IC Pin.
7. Single point grounding (refers to protective grounding, working grounding, and DC grounding are separated from each other on the equipment, and each becomes an independent system.)
8. Fuse action.
9. Ground and digital ground single point grounding.
As long as it is ground, it will eventually be received together and then into the earth. If they are not connected together, they are "floating", there is a pressure difference, and it is easy to accumulate electric charges and cause static electricity. The ground is referenced to 0 potential, all voltages are derived from reference ground, the ground standards are the same, so the various grounds should be shorted together. It is believed that the earth can absorb all the electric charges and always maintain stability, which is the ultimate ground reference point. Although some boards are not connected to the earth, the power plant is connected to the earth, and the power supply on the board will eventually return to the power plant. If the analog ground and the digital ground are directly connected to each other, it will cause mutual interference. It is not short-circuited and not appropriate. There are four ways to solve this problem as above:
(1) Connected by magnetic beads;
(2) Connected by a capacitor;
(3) Connected by an inductor;
(4) Connect with a 0 ohm resistor.
The equivalent circuit of the magnetic bead is equivalent to the band-stopper, which only significantly suppresses the noise of a certain frequency point. When using it, it is necessary to estimate the noise frequency in advance so that the appropriate model can be selected. For cases where the frequency is uncertain or unpredictable, the beads do not fit.
The capacitor is connected straight to the ground, causing floating.
The inductor is bulky, has many stray parameters, and is unstable.
The 0 ohm resistor is equivalent to a very narrow current path, which effectively limits the loop current and suppresses noise. The resistor has an attenuation in all frequency bands (0 ohm resistor also has impedance), which is stronger than the magnetic beads.
The following two figures are a circuit, just because the components are not labeled the same. R7 (R33) is a single-point link end for analog ground and digital ground.
10. For current circuit when bridging
When the ground plane is divided, the shortest return path of the signal is broken. At this time, the signal loop has to be detoured to form a large loop area, and the influence of the electric field and the magnetic field becomes stronger, which is easy to interfere/interfere. By connecting a 0 ohm resistor across the partition, a shorter return path can be provided to reduce interference.
11. Configuration circuit
Generally, there should be no jumpers or dip switches on the product. Sometimes the user will tamper with the settings, which may cause misunderstanding. In order to reduce the maintenance cost, the 0 ohm resistor is used instead of the jumper to solder on the board.
The vacant jumper is equivalent to the antenna at high frequencies, and the effect of the chip resistor is good.
12. Other uses
Overlay when wiring;
Temporarily replace other patch devices;
As a temperature compensation device;
More often than not, it is due to EMC countermeasures. In addition, the 0 ohm resistor is less than the parasitic inductance of the via, and the via also affects the ground plane (because the hole is to be dug).
There is also a different size 0 ohm resistor to allow different currents, generally 0603 1A, 0805 2A, so different currents will choose different sizes, there are reserved positions for magnetic beads, inductors, etc., according to magnetic beads, inductors The size is also packaged, so 0603, 0805 and other different sizes are available.