First, 0 ohm resistance
I often see the resistance of 0 Euro in the circuit design. Everyone will tend to be confused: since it is a resistance of 0 Euro, that is, the wire, why to install it? Is there any such resistance market? In fact, 0 Euro resistors are still quite useful. There are about a few of the following features, the most important and frequent features:
Key introduction: simulate ground and digitally single-point grounding
As long as it is, it will eventually receive it together, then enter the earth. If it is not connected, it is "floating", there is a pressure difference, and it is easy to accumulate charge, resulting in static electricity. The ground is referenced to 0 potential, all voltages are obtained, and the standards of the ground should be consistent, so they should be shorted together. It is believed that the earth can absorb all charges and always maintain stability, which is the final reference point. Although some boards do not pick up the earth, the power plant is connected to the ground, the power supply on the board will eventually return to the power plant. If the large area of the simulated ground and the digital ground is directly connected, it can cause mutual interference. No shortcomings, unclepture, the reason has four methods to solve this problem:
1, connect with a magnetic bead;
2, use capacitance connection;
3, use inductive connections;
4, connect with 0 ohm resistors.
Difference:
1. The equivalent circuit of the magnetic bead is equivalent to the band resistance wave, only has a significant suppression effect on the noise of a certain frequency point, and the noise frequency needs to be pre-estimated in order to select the appropriate model. The magnetic beads are not in combination with frequencies of frequencies or unprofitable.
2, capacitive intercept, causing floating ground.
3, large inductance volume, more spurious parameters, unstable.
4, 0 Euro resistance is equivalent to a very narrow current path, which can effectively limit loop current to suppress noise. The resistor has attenuation effect on all frequency bands (0 Euro resistors also have impedances), which is stronger than the beads.
Other effects of 0 ohm resistance
1, there is no function in the circuit, just for the convenience or compatibility design in the PCB.
2, you can do jumper, if a certain line is not used, you can do not post the resistance (not affecting the appearance).
3, when the matching circuit parameters are uncertain, in an amount of 0 ohms, when actually debug, determine the parameters, and then replace the component of the specific value.
4, when measuring the current of a partial circuit, you can remove the 0OHM resistor, attach the current table, which is convenient for the current. ,
5, when the wiring, if it is not in the unique, you can add a 12 Euro resistance.
6, under high frequency signals, act as inductance or capacitance. (Related to external circuit characteristics) The inductor is mainly to solve the EMC problem. For example, power and IC, PIN,
7, single-point grounding (referring to protecting grounding, work grounding, DC grounding is separated from each other on equipment, each is independent system.),
8, fuse,
⑨, use for current circuit when crossing
When the electrical plane is divided, the shortest reflow path breaks the signal, at this time, the signal circuit has to detour, forming a large loop area, the effect of electric field, and magnetic fields, is easy to interfere with / interfered. A shorter return path can be provided in the divided area to provide a shorter return path to reduce interference.
⑩, configuration circuit
Generally, do not appear on the product, the jumper and dialing switch. Sometimes the user will make settings, easy to cause misuse, in order to reduce maintenance costs, apply 0 Euro resistance replacement and other welds on the board. The vacant jumper is equivalent to the antenna at high frequencies, with a patch resistance effect.
⑾, other uses
Time to route, debug / test, temporarily replace other chip devices, as temperature compensation devices, more time for EMC countermeasures. In addition, 0 ohmic resistance is small inductance than the passage of the hole, and the via holes will affect the plane (because of the need to dig), there is a different size of 0 Euro resistors to pass the current, general 0603 1A, 0805, 2A Therefore, different currents will use different sizes. In addition, it is a reserved position such as magnetic beads and inductors, and it has been packaged according to the magnetic beads and inductance, so there are different sizes such as 0603, 0805.
Attachment: 1 ohmic resistance
1 ohm resistor is often used in the circuit, for example, when we need to measure the current in a circuit, we can struck one ohmic resistance in the circuit, measure the voltage of both ends of the circuit (i = U / R because r = 1, so the measured voltage value is a current value).
Second, the magnetic beads:
Magnetic beads are dedicated to suppressing signal lines, high frequency noise and spike interference on the power line, and also having the ability to absorb electrostatic pulses. Magnetic beads are used to absorb ultra-high frequency signals, like some RF circuits, PLLs, oscillating circuits, ultra-high-frequency memory circuits (DDR, SDRAM, RAMBUS, etc.) need to add magazines in power input portions, while inductance is a kind of The energy storage element is used in the LC oscillation circuit, the low frequency filter circuit, and the like, and its application frequency ranges exceeds 50 MHz. The magnetic beads have a high resistivity and magnetic permeability, equivalent to resistance and inductance, but the resistance value and inductance value varies with frequency.
The function of the magnetic beads: mainly eliminating RF noise existing in the transmission line structure (circuit), RF energy is superimposed on AC sine wave ingredients on the direct current transmission level, and the DC component is a useful signal, while the radio frequency RF energy is Useless electromagnetic interference along line transmission and radiation (EMI). To eliminate these unwanted signal energy, use a slice magnetic bead to play a high-frequency resistor role (attenuator) that allows the DC signal to pass, and filter out the AC signal. Usually the high frequency signal is 30 MHz or more, however, the low frequency signal is also affected by sheet magnetic beads.
Magnetic beads have a high resistivity and magnetic permeability, which is equivalent to resistance and inductance, but the resistance value and inductance value varies with frequency. It has a better high frequency filtering characteristic than ordinary inductance, which is resistant to high frequency, so that high impedance can be maintained within a fairly wide frequency range, thereby increasing the frequency modulated filtering effect. ,
As the power filter, an inductor can be used. The circuit symbol of the magnetic bead is the inductor but can be seen on the model that the magnetic beads are in the circuit function, the magnetic beads and inductors are the same, only the frequency characteristics are different.
Note: The unit of the magnetic bead is ohm, not Henry, this should pay special attention.
Third, inductance
Inductance is an attribute of closing loop. When the coil passes the current, the magnetic field induction is formed in the coil, and the induction magnetic field generates an induction current to resist the current in the coil. This relationship between this current and coil is called electrical impedance, that is, inductance, unit is "Henry (H)".
Note: About the inductance only, this content is reflected in the following.
Difference between magnetic beads and inductance
Inductors are energy storage components, and magnetic beads are energy conversion (consumption) devices. Inductance is mostly used in power filter circuits, focusing on suppression of conductive interference; magnetic beads are mostly used for signal circuit, mainly for EMI. Magnetic beads are used to absorb ultra-high frequency signals, like some RF circuits, PLLs, oscillating circuits, ultra-high-frequency memory circuits (DDR, SDRAM, RAMBUS, etc.) need to add magazines in power input portions, while inductance is a storage The energy component is used in the LC oscillation circuit, the medium and low frequency filter circuit, and the like, its application frequency ranges exceeds 50 MHz. In the circuit function, the magnetic beads and inductors are the same, only the frequency characteristics are different.
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