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| Murata magnetic beads, application in ultra-high frequency signals |
| 2019-10-14 |
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Murata magnetic beads are used to absorb ultra-high frequency signals, such as some RF circuits, PLLs, oscillating circuits, and ultra-high-frequency memory circuits (DDR SDRAM, RAMBUS, etc.) all need to add Murata magnetic beads in the power input section, and the inductance is one. The energy storage component is used in the LC oscillating circuit, the low-frequency filter circuit, etc., and its application frequency range rarely exceeds 50 MHz.
The function of Murata magnetic beads is mainly to eliminate the RF noise existing in the transmission line structure (circuit). The RF energy is the AC sine wave component superimposed on the DC transmission level. The DC component is the useful signal required, while the RF RF energy is Useless electromagnetic interference is transmitted along the line and radiated (EMI). To eliminate these unwanted signal energies, use the chip Murata magnetic beads to act as a high-frequency resistor (attenuator) that allows the DC signal to pass and filter out the AC signal. Usually the high frequency signal is above 30MHz, however, the low frequency signal will also be affected by the chip Murata magnetic beads.
The chip Murata magnetic beads are composed of soft ferrite materials, which constitute a monolithic structure with high volume resistivity. The eddy current loss is inversely proportional to the resistivity of the ferrite material. The eddy current loss is proportional to the square of the signal frequency. Benefits of using chip Murata magnetic beads: Miniaturization and lightweighting have high impedance in the RF noise frequency range, eliminating electromagnetic interference in the transmission line. Close the magnetic circuit structure to better eliminate the crosstalk of the signal. Excellent magnetic shielding structure. Reduce the DC resistance to avoid excessive attenuation of the wanted signal. Significant high frequency and impedance characteristics (better elimination of RF energy). Parasitic oscillations are eliminated in the high frequency amplifying circuit. Effective operation ranges from a few MHz to a few hundred MHz.
To correctly select Murata magnetic beads, you must pay attention to the following points:
1. What is the frequency range of the unwanted signal;
2. Who is the noise source?
3. How much noise attenuation is needed;
4. What are the environmental conditions (temperature, DC voltage, structural strength);
5. What is the circuit and load impedance;
6. Is there room for the Murata magnetic beads to be placed on the PCB;
The first three can be judged by observing the impedance frequency curve provided by the manufacturer. All three curves in the impedance curve are very important, namely resistance, inductive reactance and total impedance. The total impedance is described by ZR22πfL()2+:=fL. Through this curve, the Murata magnetic bead model has the largest impedance in the frequency range where noise is desired to be attenuated and the signal attenuation is as small as possible under low frequency and direct current. The impedance of the chip Murata magnetic beads will be affected under excessive DC voltage. In addition, if the operating temperature rises too high or the external magnetic field is too large, the impedance of Murata magnetic beads will be adversely affected. Reasons for using chip Murata magnetic beads and chip inductors: Whether to use chip Murata magnetic beads or chip inductors is mainly in application. A chip inductor is required in the resonant circuit. When it is necessary to eliminate unwanted EMI noise, the use of chip Murata magnetic beads is the best choice.
Application of chip Murata magnetic beads and chip inductors:
Chip inductors: Radio frequency (RF) and wireless communications, information technology equipment, radar detectors, automobiles, cellular phones, pagers, audio equipment, PDAs (personal digital assistants), wireless remote control systems and low voltage power supply modules.
Chip Murata Beads: Clock generation circuit, filtering between analog circuit and digital circuit, I/O input/output internal connector (such as serial port, parallel port, keyboard, mouse, long distance telecommunication, local area network), radio frequency (RF) Between the circuit and the susceptible logic device, the high-frequency conduction interference is filtered out in the power supply circuit, and the EMI noise in the computer, the machine, the video recorder (VCRS), the television system, and the mobile phone is suppressed.
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