Bead
bead materials are iron or iron-magnesium-nickel alloy, having generally these materials have high electrical resistivity and magnetic permeability at high frequencies and high impedance, the capacitance between the inductor will be minimized. Beads usually only suitable for high frequency circuit, because at low frequencies, which are substantially retain characteristic of the inductance of the complete (with resistive and reactive components), thus resulting in a slight loss of the line. While at high frequencies, which has a reactive component substantially only (jωL), and the resistance component increases with frequency increase.
Like some of the RF circuit, PLL, oscillation circuit, a memory circuit containing ultra-high frequency (DDR, SDRAM, RAMBUS, etc.) need to increase the power input portion beads. Indeed, the beads are high-frequency attenuator of RF energy. In fact, the beads may be considered as a resistor in parallel with an inductor. At low frequencies, the inductor resistance is "short circuit", the current flowing to the inductor; at high frequencies, the high inductance of the inductor forces the current flows to the resistor. Essentially, the magnetic beads is a "dissipative device (dissipative device)", which high frequency energy is converted into heat. Thus, the performance, which can only be interpreted as a resistance, inductance instead.
Inductance of
the inductor is an energy storage element, used for power supply filtering circuit, the LC oscillator circuit, low-frequency filter circuit, the frequency range of application rarely exceeds 50MHz. For the inductor, and its inductance is proportional to the frequency of. This may be by the formula: XL = 2πfL be described, wherein XL is the inductive reactance (the unit is Ω). For example: An ideal 10mH inductor, at 10kHz, inductance is 628Ω; at 100MHz, increased 6.2MΩ. Therefore, when 100MHz, this inductance can be regarded as open (open circuit). When 100MHz, so that if a signal through this inductance will cause the signal quality decreases.
0R resistance
refers to resistance of the resistor is zero. Board design points can not be connected with a printed circuit, with the front often connected across the line, which is often seen in normal plate, in order to allow automatic placement machine and the automatic plug work, instead of across the line with zero resistance.
0R resistance effect is generally on the PCB.
1, no function in the circuit, only for debugging design convenience or other reasons compatible on the PCB.
2, can be done by a jumper, if not certain lines, the resistance to direct subsidies (not affect the appearance).
3, the matching circuit when the uncertain parameters to 0ohm instead of actual debugging time, to determine the parameters, and then replaced by elements of specific values.
4, to measure the current consumption of the circuit when a portion can be removed 0ohm resistance ammeter connected, so that the measured current consumption of convenience.
5, in the wiring, if it is not passed cloth, a resistor may be added 0ohm (the sense line should be used, and should not be affixed to the table (luther.gliethttp)).
6, the high-frequency signal, serving as inductive or capacitive. (With the external characteristics of the circuit) with inductance, mainly to solve EMC problems. (E.g. between the ground, and the power supply IC Pin).
7, single-point ground (grounding means protection, grounding, separated from each other in the DC ground equipment, each as an independent system).
0R mentioned resistors and magnetic beads, single-point ground certainly want to address problems of analog and digital ground.
As long as the ground, we will eventually be tied together, and then into the earth. If you are not together is "floating", there is pressure, easy to accumulate electric charge, resulting in static electricity. 0 is the reference potential, the reference voltages are derived for all of the criteria to be consistent, it should be shorted together variously. It is believed that the earth can absorb all the charges, has remained stable, is the ultimate ground test sites. Although some board did not take the land, but power plants are connected to the earth, and power on the board will eventually return to power plants into the ground. If the analog and digital grounds directly connected to a large area, it can cause interference. And less then wrong, there are four reasons described above resolve this problem:
1, is connected with the magnetic beads; bead equivalent circuit corresponding to a band stop limiter wave, only significant suppression of noise in a frequency effect, required the use of pre-estimated frequency noise, in order to choose the appropriate model. In the case of frequency uncertain or unpredictable, beads substandard.
2, is connected with the capacitor; cross-blocking capacitor through easily lead floating.
3, the connection inductance; inductance large volume, multi-parasitics, unstable.
4, zero-ohm resistor connected; zero-ohm resistor corresponding to very narrow current path, the loop current can be effectively restrained, so that noise is suppressed. Resistance on all bands have a damping effect (also zero ohm impedance), this is stronger than the magnetic beads.
