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In simple terms, the number is part of the public the benchmark side of digital circuit, namely the benchmark end of the digital voltage signal; Simulation to benchmark is analog part of the public side, the analog signals of voltage reference end (zero point),
One, is divided into the cause of the digital earth and simulation:
Because the digital signal for the rectangular wave, usually with a large number of harmonics, if digital earth and simulation of circuit board did not divide from the access point, the harmonic wave is easy to interfere with the digital signal to analog signal waveform, when analog signal of high frequency or high voltage signal, will also affect the normal work of the digital circuits, analog circuits involving weak signal, but the digital circuit threshold level is higher, the requirement to the power supply is lower than the analog circuit, there are both digital circuit and analog circuit system, the digital circuit will affect the noise emitted by analog circuits, the index of analog circuit of small signal variation, overcome way is to separate analog and digital,
The root cause of the problem is that there is no guarantee that the resistance of the circuit board copper foil is zero, the access point will be digital and analog to separate, for the total will be digital and analog ground to minimize resistance,
Second, digital and analog to deal with the basic principle is as follows:
If the analog ground and digital ground area directly connected, can lead to interfere with each other not short sub again wrong,
For low frequency analog circuits, in addition to bold and shorten the ground wire, circuit parts by one-point earthing is the best choice of the ground wire interference suppression, mainly due to ground public impedance can be prevented from mutual interference between parts,
For the high frequency circuit and digital circuit, because the inductance of the ground effect will be bigger, one-point earthing can lead to actual ground wire extension and bring adverse effect, then should be taken to separate grounding and a bit of a combination of,
In addition to high frequency circuit to consider how to suppress the high frequency noise, the method is: bold ground as far as possible, in order to reduce the noise on ground impedance; Full ground, that is, in addition to the transmission signal printing line, all the other parts as the ground, not to have useless large copper foil,
Ground should constitute A loop, in order to prevent high frequency radiation noise, but surrounded by A loop area is not too big, lest instruments in A strong magnetic field, produce induced current, but if only low frequency circuits, should avoid the ground loop, digital power supply and analog power supply isolation, best separate ground is decorated, if there is A A/D, only in single point here,
In the low frequency have little effect, but suggested that analog and digital ground, high frequency, the analog and digital ground by magnetic beads point total,
Three, four kinds of solutions
Analog ground and digital ground between concatenated
1) connection with magnetic beads; 2) using capacitance connected; 3) with inductance connection; 4) with zero ohm resistance connection,
1. The inductance generally use several uH to dozens of uH,
2. Use 0 the resistance is the best choice for
A. ensures equal dc potential
B. single point grounding (limit noise)
C. in all frequency noise attenuation effect (0 the also have impedance and current path narrow, can limit the noise current through),
Magnetic beads
3.Used in high frequency band with good sintered ferrite material surface impedance characteristics, dedicated to suppress the signal lines, the high frequency noise in the power cord and peak interference, have the ability to absorb electrostatic pulse,
The main parameters:
Nominal value: because the unit of magnetic beads are according to it at a particular frequency impedance to nominal, the unit of impedance is the ohm. Generally it is a standard with 100 MHZ, 2012 b601, for example, is refers to the impedance of the magnetic beads at 100 MHZ to 600 ohms,
Rated current, rated current is to point to to guarantee the normal work of the circuit is allowed by current.
Magnetic beads has high resistivity and magnetic conductivity, he equivalent resistance and inductance in series, but the resistance and inductance are changing with frequency, inductance are better than ordinary high-frequency filtering properties, when high frequency impedance, so can in quite a wide frequency range to keep high impedance, so as to improve the effect of frequency modulation filter, magnetic beads can have larger block of the high frequency signal, the general specification 100 o/100 MMHZ, it resistance than in low frequency inductor, Ferrite Bead, Ferrite Bead) is one of the current application development soon anti-interference components, cheap, easy to use, high frequency noise filtering effect is significant,
Some have multiple holes, magnetic beads with wires through the components can increase the impedance (the number of times square through the magnetic beads), but the increase in high frequency noise suppression ability could not as expected, with several magnetic beads series way will be better, ferrite magnetic materials, can produce because of current through the magnetic saturation, permeability fell sharply, large current filter structure should be adopted on specially designed magnetic beads, also notice its cooling measures,
Ferrite beads not only can be used to filter out high frequency noise in the power circuit (can be used in the dc and ac output), also can be widely applied to other circuit, the volume can be very small, especially in the digital circuit, due to the pulse signal with high order harmonic frequency is very high, is also a main circuit of high frequency radiation source, so can play the role of magnetic beads in this situation,
As long as the wire in the circuit through it, when the current through the wire, the little ferrite of low frequency current impedance, and will produce large attenuation of high frequency current, high frequency current in which distributed in the form of heat, its equivalent circuit is an inductance and a resistance in series, both the values of the component and is proportional to the length of the magnetic beads, magnetic bead is a lot of more phyletic, the manufacturer shall provide technical indicators, especially the relationship between impedance and frequency of magnetic beads curve,
4. The capacitance
By using the principle of capacitance direct hand in isolation,
4. The difference between the inductance and magnetic beads:
Have more than one turn coil habit called inductance coil, less than one turn (wire through the circular) used to call by the coil in the magnetic beads; Inductive energy storage component, and magnetic beads is energy conversion (consumption) device; Inductance used in power supply filter circuit, magnetic beads for signal circuit, used for EMC countermeasure; Magnetic beads are mainly used for electromagnetic radiation interference suppression, and inductance used in this respect is focus on the conductive interference suppression. Both can be used to deal with the EMC and EMI problems; Inductance is commonly used in control circuit matching and signal quality. Where the analog and digital integrated with magnetic beads,
As a power supply filter, you can use the inductance, magnetic beads is inductance circuit symbols but models can be seen on the use of magnetic beads on the circuit function, magnetic beads and principle of inductance is the same, just different frequency characteristics; Magnetic beads is composed of oxygen magnets, inductance consists of core and coil, a magnetic bead the ac signal is converted into heat energy, inductance store communication, slow release,
Inductive energy storage component, and magnetic beads is energy conversion (consumption) device; Inductance used in power supply filter circuit, magnetic beads for signal circuit, used for EMC countermeasure; Magnetic beads are mainly used for electromagnetic radiation interference suppression, and inductance used in this respect is focus on the conductive interference suppression, both can be used to deal with the EMC and EMI problems,
Magnetic beads are used to absorb the uhf signals, like some RF circuit, PLL, oscillating circuit, including uhf memory circuit (DDR SDRAM, RAMBUS) needs to be in power input part and magnetic beads, and inductance is a kind of energy storage component, used in LC oscillation circuit, the low frequency of the filter circuit, etc., and its application range rarely more than 50 MHZ,
Five, several methods were
Capacitance between direct delivery, floating, not dc capacitance, will lead to differential pressure and static accumulation, will touch the chassis hemp hand, if the shunt capacitance and magnetic beads, not necessary, because the magnetic beads straight, capacitance will fail, the series is neither fish nor fowl,
Inductance is big, stray parameters, characteristics is not stable, discrete distribution parameters is bad control, large volume, inductance is trap, LC resonance (capacitance), has special effects to the noise,
Magnetic beads of the equivalent circuit of band-stop trap, only showed inhibitory effect on the noise of a certain frequency point, if you can't predict noise, how to choose the model, furthermore, noise frequency is not fixed, so the magnetic beads is not a good choice,
0 the resistor is equal to the current path is very narrow, can effectively restrict the loop current, make the noise, be suppressed, resistance have attenuation effect on all band (0 the resistance have impedance), it is better than magnetic beads,
In short, the key is the analog ground and digital ground to one-point earthing, suggested that different types are connected with 0 the resistance; Power supply is introduced into the high frequency components with magnetic beads; High frequency signal coupled with a small capacitance; Inductance used in high power low frequency,