Magnetic beads are designed to suppress high-frequency noise and spike interference on signal and power lines on PCB boards, as well as to absorb electrostatic pulses. They are commonly used to absorb ultra-high frequency signals in RF circuits, PLLs, oscillator circuits, and ultra-high frequency memory circuits such as DDR SDRAM and RAMBUS. Magnetic beads are typically added to the power input port of these circuits as a form of inductance storage.
They are also used in LC oscillator circuits, medium and low frequency filter circuits, and other applications where the frequency range does not exceed 50MHz. The primary function of magnetic beads is to eliminate RF noise in the transmission line structure of PCB circuits. RF energy is the AC sine wave component superimposed on the DC transmission level. While the DC component represents the desired useful signal, the RF energy is essentially useless electromagnetic interference that can lead to transmission and radiation (EMI) issues along the line.
To mitigate this interference, chip beads are employed as high-frequency resistors (attenuators) that allow DC signals to pass through while filtering out AC signals. While chip beads are commonly used for high-frequency signals above 30MHz, they can also have an impact on low-frequency signals.
The chip magnetic bead is composed of soft ferrite material, which forms a monolithic structure with high volume resistivity. Eddy current losses are inversely proportional to the resistivity of the ferrite material and proportional to the square of the signal frequency. Chip beads offer benefits such as miniaturization, lightweight design, high impedance in the RF noise frequency range for eliminating EMI in transmission lines, a closed magnetic circuit structure for better elimination of signal cross-winding, and an excellent magnetic shielding structure. They also reduce DC resistance to prevent excessive attenuation of the useful signal, provide remarkable high-frequency characteristics and impedance characteristics, and ensure effective operation in the frequency range of a few MHz to several hundred MHz.
To correctly select magnetic beads, attention must be paid to the following points:
1. Determine the frequency range of the unwanted signal.
2. Identify the noise source.
3. Determine the required noise attenuation.
4. Consider environmental conditions such as temperature, DC voltage, and structural strength.
5. Evaluate the circuit and load impedance.
6. Ensure there is space on the PCB board to place magnetic beads.
The first three points can be assessed by examining the impedance frequency curve provided by the manufacturer. The impedance curve comprises resistance, inductive reactance, and total impedance. Choose a bead model based on impedance in the frequency range where noise attenuation is needed while minimizing signal attenuation at low frequencies and DC. Chip magnetic beads’ impedance characteristics may be affected by excessive DC voltage, high working temperatures, or large external magnetic fields.
The decision to use chip beads or chip inductors depends on the application. Chip inductors are necessary in resonant circuits, while chip beads are preferred for eliminating unwanted EMI noise. Common applications include:
Chip inductors: RF and wireless communications, information technology equipment, radar detectors, automotive electronics, cellular phones, pagers, audio equipment, PDAs, wireless remote control systems, and low-voltage power supply modules.
Chip beads: clock generation circuits, filtering between analog and digital circuits, I/O internal connectors (e.g., serial ports, parallel ports, keyboards, mice), long-distance telecommunications, local area networks, RF circuits, interference-prone logic devices, high-frequency conducted interference filtering in power supply circuits, EMI noise suppression in computers, printers, VCRs, television systems, and mobile phones on PCB boards.
They are also used in LC oscillator circuits, medium and low frequency filter circuits, and other applications where the frequency range does not exceed 50MHz. The primary function of magnetic beads is to eliminate RF noise in the transmission line structure of PCB circuits. RF energy is the AC sine wave component superimposed on the DC transmission level. While the DC component represents the desired useful signal, the RF energy is essentially useless electromagnetic interference that can lead to transmission and radiation (EMI) issues along the line.
To mitigate this interference, chip beads are employed as high-frequency resistors (attenuators) that allow DC signals to pass through while filtering out AC signals. While chip beads are commonly used for high-frequency signals above 30MHz, they can also have an impact on low-frequency signals.
The chip magnetic bead is composed of soft ferrite material, which forms a monolithic structure with high volume resistivity. Eddy current losses are inversely proportional to the resistivity of the ferrite material and proportional to the square of the signal frequency. Chip beads offer benefits such as miniaturization, lightweight design, high impedance in the RF noise frequency range for eliminating EMI in transmission lines, a closed magnetic circuit structure for better elimination of signal cross-winding, and an excellent magnetic shielding structure. They also reduce DC resistance to prevent excessive attenuation of the useful signal, provide remarkable high-frequency characteristics and impedance characteristics, and ensure effective operation in the frequency range of a few MHz to several hundred MHz.
To correctly select magnetic beads, attention must be paid to the following points:
1. Determine the frequency range of the unwanted signal.
2. Identify the noise source.
3. Determine the required noise attenuation.
4. Consider environmental conditions such as temperature, DC voltage, and structural strength.
5. Evaluate the circuit and load impedance.
6. Ensure there is space on the PCB board to place magnetic beads.
The first three points can be assessed by examining the impedance frequency curve provided by the manufacturer. The impedance curve comprises resistance, inductive reactance, and total impedance. Choose a bead model based on impedance in the frequency range where noise attenuation is needed while minimizing signal attenuation at low frequencies and DC. Chip magnetic beads’ impedance characteristics may be affected by excessive DC voltage, high working temperatures, or large external magnetic fields.
The decision to use chip beads or chip inductors depends on the application. Chip inductors are necessary in resonant circuits, while chip beads are preferred for eliminating unwanted EMI noise. Common applications include:
Chip inductors: RF and wireless communications, information technology equipment, radar detectors, automotive electronics, cellular phones, pagers, audio equipment, PDAs, wireless remote control systems, and low-voltage power supply modules.
Chip beads: clock generation circuits, filtering between analog and digital circuits, I/O internal connectors (e.g., serial ports, parallel ports, keyboards, mice), long-distance telecommunications, local area networks, RF circuits, interference-prone logic devices, high-frequency conducted interference filtering in power supply circuits, EMI noise suppression in computers, printers, VCRs, television systems, and mobile phones on PCB boards.