Inductance, bead, 0 ohm resistor

Magnetic beads

Magnetic beads (ferrite bead) materials are iron-magnesium or iron-nickel alloys, these materials have a high resistivity and permeability, at high frequencies and high impedance, inductance in the inner ring between the capacitance value will be minimal. Beads are usually only suitable for high-frequency circuits, because at low frequencies they are essentially the complete characteristics of the inductor (including the resistive and reactive components), which can cause a slight loss on the line. At high frequencies, it basically only has a reactive component (JΩL), and the resistance component increases as the frequency rises. Like some RF circuits, PLLs, oscillation circuits, including UHF memory circuits (Ddr,sdram,rambus, etc.) are required to add magnetic beads to the Power input section. In fact, a magnetic bead is a high frequency attenuator of RF energy. In fact, a magnetic bead can be considered as a resistor in parallel with an inductor. At low frequencies, the resistor is "shorted" by the inductor, and the current flows toward the inductor, at high frequencies, the high inductance of the inductor forces the current to flow to the resistor. Essentially, a bead is a "dissipative device (dissipative device)" That converts high-frequency energy into heat. Therefore, in performance, it can only be interpreted as a resistor, not an inductor.

inductance

Inductor is a energy storage element, many for the Power filter circuit, LC oscillation circuit, low-frequency filter circuit, etc., its application frequency range is rarely more than 50MHz. For inductance, its inductance is proportional to the frequency. This can be illustrated by the formula: XL = 2ΠFL, where XL is inductance (unit is ω). For example: An ideal 10mH inductor, at 10kHz, inductance is 628ω; at 100MHz, increase to 6.2mω. Therefore, at 100MHz, the inductor can be considered an open (open circuit). At 100MHz, if a signal is passed through this inductor, it will result in a decrease in the quality of this signal.

0 Ohm

Refers to a resistor with zero resistance. Circuit board design two points can not be connected with the printed circuit, often in the front with cross-line connection, which is often seen in the ordinary board, in order to allow automatic Mounter and automatic plug-in machine to work properly, with 0 resistors instead of cross-line.

The effect of the 0 ohm resistor is as follows:

1, in the circuit does not have any function, just on the PCB for debugging convenience or compatible design and other reasons.

2, can do jumper, if a segment of the line is not used, directly subsidize the resistor can (not affect the appearance).

3, when the matching circuit parameters are uncertain, to replace the 0ohm, the actual commissioning, the determination of parameters, and then the specific values of the components instead.

4, want to measure a part of the circuit power consumption, you can remove the 0ohm resistor, connected to the ammeter, so as to facilitate the measurement of power flow.

5, in the wiring, if the actual cloth does not pass, you can also add a 0ohm resistor (feel should be inserted, should not be the table sticker (luther.gliethttp)).

6, in the high-frequency signal, acting as inductance or capacitance. Inductors (related to external circuit characteristics) are primarily used to solve EMC problems. (e.g. ground to ground, power supply and IC pin).

7, the single point of grounding (refers to the protection of ground, work ground, DC grounding on the device to separate each other, respectively become independent system).

8, Fuse action inductor

① analog ground and digital ground single point grounding

As long as it is the ground, eventually will have to receive together, and then into the earth. If not joined together is "floating", there is a pressure difference, easy to accumulate electric charge, causing static electricity. The ground is to refer to 0 potential, all voltages are referenced to the ground, the standard to be consistent, so all kinds of ground should be short-connected together. It is believed that the earth can absorb all electric charges and remain stable at all times, and is the final Test ground. Although some boards do not connect the Earth, but the power plant is connected to the Earth, the board will eventually return to the electricity plant into the ground. If the simulated ground and the large area of the digital directly connected, will cause mutual interference. There are four ways to solve this problem:

1, with magnetic beads connected, the equivalent circuit of magnetic beads equivalent to band-stop limiter, only a certain frequency point of the noise has a significant inhibition, the use of the need to pre-estimate the noise frequency, in order to choose the appropriate model. For situations where the frequency is uncertain or unpredictable, the bead does not fit.

2, the electric capacitance connection, the capacitor pass through, easy to cause the floating ground.

3, electricity sense connection, inductance volume, spurious parameters are many, unstable.

4, with 0 ohm resistor connection, 0 ohms equivalent to a very narrow current path, can effectively limit the loop current, so that the noise is suppressed. Resistance is attenuated in all frequency bands (0 ohms also has impedance), which is stronger than magnetic beads.

② for current loops during cross-connect

When the ground plane is divided, resulting in the shortest return path of signal rupture, at this time, the signal loop has to bypass, forming a large loop area, the effect of electric field and magnetic field becomes stronger, easy to interfere/be disturbed. Bridging the 0 ohm resistor across the partition provides a shorter return path and reduces interference.

③ Configuration Circuit

In general, do not appear on the product jumper and dial switch. Sometimes users will tamper with the settings, easy to cause misunderstanding, in order to reduce maintenance costs, the use of 0 ohms instead of jumpers and other welding on the board. The vacant jumper is equivalent to the antenna at high frequency, and the effect is good with SMD resistance.

④ Other uses:

A, wiring, cross-line B, debugging/testing C, temporarily replace the other SMD device D, as a temperature compensation

The device is more often out of the need for EMC countermeasures. In addition, the 0 ohm resistor is smaller than the parasitic inductance of the vias, and the vias also affect the ground plane (because digging holes).

Inductance, bead, 0 ohm resistor