# Analog location and digital location)

Source: Internet
Author: User

Http://www.eetop.cn/blog/html/48/108448-21685.html

In fact, the essence is right, that is, the numbers and analog places are both places. It's not that the two of them have a long angle on their heads. It's very strange. You need to understand why you need to separate them. First, let me tell a story.
The business building of our company is located on the third floor, the second floor is simulated, and the third floor is digital. There is only one elevator in the whole building. When there are few people at ordinary times, we can handle it on the second floor, on the third floor, there is no image of each other, but it is very difficult to go to or from work every morning. There are many people. The number of people on the third floor is always affected by the simulation on the second floor, the simulated persons on the second floor are going to go downstairs. They always have to wait for the elevator to go to the third floor. It is very troublesome to affect each other,
In order to solve this problem, the business building property has proposed two solutions,
1st million (laughing)
The elevator expands and more people can be installed,
The elevator is good, but the company will recruit more people, there are more people, then change the elevator, then recruit people... there is always an endless loop, and there is a good way to do it. Everyone simply doesn't want to take the elevator and jump down directly. No matter whether it's on the second or third floor, it will definitely solve the problem, but there will certainly be problems (1st were shot down)
2nd
Install two elevators, one on the second floor and the other on the third floor.
Wonderful! This is so witty that the staff on the two floors will not affect each other.
End
Do you understand?

The simulated place influences each other not because it is a number or a simulation, but because they use the same elevator-location, the well used by this elevator is the ground wire we laid on the PCB.
The current of the Analog Loop follows this line, and the current of the digital loop follows this line. It is understandable that the wire is used to turn on the current, but the problem is that there is a resistance on this line!
The most fundamental problem is that the current going through this line is going to two different circuits.
Suppose there are two currents, a digital stream, and a model stream starting from the ground at the same time. There are 2 devices, several devices, and modules.
If the two circuits are not separated, the loss voltage is V when the model flow is back to the front of the grounding end of the several parts.
V = (digital stream + die stream) x wire resistance
It is equivalent to increasing the grounding end of the digital device to the ground end.
The digital device is not satisfied. I admit that it will increase a little voltage. I recognize the part of the digital stream, but why should the model stream be added to my head?
Similarly, the simulator will also complain.
2 solutions
1st: the PCB line you deploy has no impedance and will naturally not cause interference, just as the 2 and 3 floors jump down directly. That is the widest time of the well, that is, an infinite elevator can be installed. Naturally, no one will affect anyone, but everyone knows that this is Mission Impossible.
2nd: two circuits are separated, the number of streams and the mode stream are separated, which are separated by both the number and mode.
Similarly, although it is sometimes in a simulated loop, it must be divided into large and small current circuits to avoid mutual interference.
The so-called interference is the voltage caused by the current of two different circuits on the PCB going online. These two voltages are superimposed on each other.
To put it simply, a digital location is the opposite of a digital signal, and a simulated location is the opposite of a analog signal.
Because the digital signal is generally a rectangular wave, it carries a large number of harmonic waves. If
The digital and analog locations are not separated from the access point, and the harmonic in the digital signal can easily
Waveforms that interfere with analog signals. When the analog signal is a high-frequency or strong electrical signal
Affects the normal operation of digital circuits.

The root cause of the problem is that no one can guarantee that the resistance of copper foil on the circuit board is zero,
When the access point is separated from the simulated place, it is used to separate the numbers from the simulated place.
The common ground resistance is minimized.

★The basic principles of digital and analog processing are as follows:

1. link between a simulated location and a digital location

(1) What is the general value of a Series-connected inductor between a simulated and a digital location?

Generally, it uses a few uh s to dozens of uh S.

(2) 0 euro resistance is the best choice (1) can ensure the DC potential is equal, (2) Single Point Grounding (limited noise), (3) it degrades noise at all frequencies (0-euro also has impedance, and the current path is narrow, which can limit the passing of noise current ).
Magnetic Beads are equivalent to band blocking traps. They only suppress noise at a certain frequency. If you cannot predict the noise, how do you choose a model? Besides, the noise frequency is not necessarily fixed. Therefore, magnetic beads are not a good choice.
The capacitor is not connected to DC, which will lead to pressure difference and accumulation of static electricity. If the capacitor and the beads are connected in parallel, it is enough to draw a snake. Because the beads are straight, the capacitor will become invalid. Concatenating data is not uncommon.
The inductance is unstable, the discrete distribution parameters are difficult to control, and the size is large. Inductance is also a trap. LC resonance (distributed capacitance) has special effects on noise.
In short, the key is to make a point of grounding between analog and digital locations.
It is recommended that 0-euro Resistance be used to connect different types of locations; magnetic beads are used when the power supply is introduced into high-frequency devices; small capacitance is used for coupling of high-frequency signal lines; inductance is used in high-power and low-frequency.

The sintered surface of ferrite with good impedance in high frequency band is used to suppress high-frequency noise and peak interference on signal lines and power cables, and to absorb electrostatic pulses.
Main parameters:
Nominal value: because the Unit of the magnetic beads is nominal according to the impedance generated at a certain frequency, the impedance unit is also ohm. generally, 100mhz is used as the standard. For example, 2012b601 indicates that the impedance of the magnetic beads is 600 ohm at 100mhz.
Rated current: The rated current is used to ensure that the circuit works normally.

3 difference between inductance and magnetic beads:
More than one turn of the coil is used to be called the Inductance Coil, less than one turn (wire through the magnetic ring) the coil habit is called magnetic beads;
Inductance is an energy storage component, while magnetic beads are an energy conversion (consumption) device;
Inductance is mostly used in power supply filtering loop, magnetic beads are mostly used in signal loop, and EMC countermeasure;
Magnetic Beads are mainly used to suppress electromagnetic radiation interference, while inductance is used to suppress conductive interference. Both can be used to handle EMC and EMI problems;
Inductance is generally used for circuit matching and signal quality control. Magnetic Beads are used in places where it is combined in analog and numerical ways.
Magnetic Beads have high resistivity and magnetic permeability, which is equivalent to a series of resistance and inductance, but the resistance value and Inductance Value Change with frequency. It has better high-frequency filtering characteristics than ordinary inductor, and presents resistance at high frequencies, so it can maintain a high impedance within a very wide frequency range, thus improving the FM filtering effect.
Inductance can be used as a power filter. The circuit symbol of the magnetic beads is inductance, but the model can be seen that the magnetic beads are used in the circuit function. The magnetic beads and the inductance are the same in principle, but the frequency characteristics are different.
Magnetic Beads are composed of oxygen magnets, and the inductance is composed of a magnetic core and a coil. The magnetic beads convert the AC signal into heat energy, and the inductance stores the AC and slowly releases it out.
Magnetic Beads have a major obstacle to high-frequency signals. Generally, the specification is 100 euro/100 mmhz, which has a much lower resistance than inductance at low frequencies.
Ferrite Bead is a fast-growing anti-interference component. It is cheap and easy to use, and has a significant effect on filtering out high-frequency noise.
In a circuit, as long as the wire passes through it (I use the ordinary resistance, the wire has passed through and glued, there is also a form of surface mount, but rarely seen sold ). When the current in the wire passes through, ferrite has almost no impedance on the low-frequency current, but it will have a great attenuation effect on the high-frequency current. High-frequency current is emitted in the form of heat. Its Equivalent circuit is a series of inductance and a resistor. The values of the two components are proportional to the length of the magnetic beads. There are many types of magnetic beads. Manufacturers should provide technical indicators, especially the curve of the relationship between impedance and frequency of magnetic beads.
Some magnetic beads have multiple holes, and the component impedance (the square of the number of beads passed) can be increased when the wires pass through. However, the noise suppression capability increased at high frequencies cannot be as expected, however, it would be better to concatenate several magnetic beads.
Ferrite is a magnetic material that produces magnetic saturation due to excessive current, resulting in a sharp reduction in the magnetic conductivity. Large Current filtering should adopt specially designed magnetic beads, and pay attention to the heat dissipation measures.
Ferrite Magnetic Beads can be used not only in power supply circuit to filter out high-frequency noise (can be used for DC and AC output), but also widely used in other circuits, and their volume can be very small. Especially in digital circuits, pulse signals contain high-frequency harmonic waves, which are also the main source of high-frequency radiation. Therefore, magnetic beads can be used in such cases.
Ferrite Magnetic Beads are also widely used in Noise Filtering of signal cables.
Take the HH-1H3216-500 commonly used in power filter as an example, the meaning of each field of the model is:
HH is a series of it, mainly used for power filter, used for signal line is HB series;
1 indicates that a component encapsulates a magnetic bead. If it is 4, it encapsulates four beads side by side;
H indicates the composition of the substance. h, C, and m are used for intermediate frequency applications (50-200 MHz ),
T low frequency applications (50 MHz), s high frequency applications (200 MHz );
3216 encapsulation size, length 3.2mm, width 1.6mm, that is, 1206 encapsulation;
500 impedance (generally MHz), 50 ohm.
There are three main product parameters:
Impedance [Z] @ 100 MHz (OHM): Typical 50, minimum 37;
DC resistance (m ohm): maximum 20;
Rated current rated current (MA): 2500.

What is the connection and difference between inductance and magnetic beads?

Inductance is an energy storage component, while magnetic beads are an energy conversion (consumption) device.

Inductance is mostly used in power supply filtering loop, magnetic beads are mostly used in signal loop, and EMC Countermeasure

Magnetic Beads are mainly used to suppress electromagnetic radiation interference, while inductance is used to suppress conductive interference. Both can be used to handle EMC and EMI problems.

Magnetic Beads are used to absorb ultra-high frequency signals, such as RF circuits, PLL, oscillating circuits, and ultra-high frequency memory circuits (ddr sdram, Rambus, etc.). They must be added to the input part of the power supply, inductance is a type of energy storage component used in LC oscillator circuit, medium and low frequency filter circuit, and its application frequency rarely exceeds the error 50 MHz.

★Generally, inductance is used for the connection of the ground, and inductance is used for the connection of the power supply, while magnetic beads are used for the signal line?
But should the magnetic beads be able to absorb high-frequency interference? In addition, after high-frequency resonance, the inductance can no longer be used ......

First, we must understand two ways of EMI: radiation and conduction. Different Ways adopt different suppression methods. The former uses magnetic beads, and the latter uses inductance.

For the I/O part of the wrench, is it possible to isolate the I/o part and the wrench location with an inductance Based on EMC, for example, how to isolate the USB location and the wrench location with a 10 h inductance to prevent the plugging noise from interfering with the ground plane?

Inductance is generally used for circuit matching and signal quality control. Use magnetic beads where it is simulated and digitally combined.

Use magnetic beads where it is simulated and digitally combined. The size of the magnetic beads between the digit and the simulated ground

Size of the magnetic beads (specifically, it should be the characteristic curve of the magnetic beads)
Depends on the frequency of the dry Disturbance Wave to be absorbed by the magnetic beads.

Why is the unit and resistance of the magnetic beads the same ?? All are Ohm !!

Magnetic Beads are high frequency blocking. Do you understand low DC resistance and high frequency resistance,
For example, 1000r @ 100mhz indicates that the signal at a frequency of 1000 m has a resistance of ohm.

Because the unit of the magnetic beads is nominal according to the impedance produced at a certain frequency, the unit of impedance is also ohm. The Datasheet of magnetic beads is usually accompanied by a characteristic curve of frequency and impedance. Generally, 100mhz is used as the standard. For example, 2012b601 indicates that the impedance of the magnetic beads is 600 ohm at MHz.

In many products, the two switches are connected with capacitors. Why is there no inductor? Are one of the two locations in the case of a shell?
I estimate (all of the following are estimates. If there are any mistakes, please advise)
If you use magnetic beads or directly connect them to the vswitch, unexpected levels such as static electricity will easily enter the place where the switch works. However, if they are disconnected, lightning strikes or other high pressures may cause sparks between the two locations to fire ...... Add a capacitor to avoid this situation. The location of the switch eliminates the harmonic through the capacitance between the two locations. Like a high-impedance transformer, he attaches a channel to eliminate harmonic! I think! Please correct me! The ferrite material is an iron-magnesium alloy or iron-nickel alloy, which has a high magnetic conductivity and can be the smallest capacitance generated between the coil winding of an inductor at a high frequency and high impedance. Ferrite Materials are usually used at high frequencies because their main inductance properties make the online loss very small. In high-frequency cases, they primarily exhibit a ratio of the impedance and change with the frequency. In practical application, ferrite material is used as a high-frequency attenuation device for RF circuits. In fact, ferrite is better equivalent to resistance and inductance parallel, low frequency resistance is short-circuited by inductance, high frequency inductance impedance becomes quite high, so that the current is all through the resistance. Ferrite is a device that consumes high-frequency energy and converts it into heat energy. This is determined by its resistance characteristics. Coil, more than one turn of magnetic beads coil used to be called Inductance Coil, less than one turn (wire through magnetic ring) coil used to be called magnetic beads. The purpose is determined by the amount of electric sensing required.

Ask: In the USB Sound Card solution of xunxun, there is also a magnetic bead on the power supply end and the ground end of UBS, I wonder if anyone knows, however, in actual production, some projects also replace magnetic beads with inductance. Is that all right?

What is the role of magnetic beads? Inductance can be used as a power filter. The circuit symbol of the magnetic beads is inductance, but the model shows that the magnetic beads are used in the circuit function. The magnetic beads and the inductance are the same in principle, but the frequency characteristics are different.

★The basic principles of digital and analog processing are as follows:

1) if it is a low-frequency analog circuit, fill in and shorten the ground line; Single Point Grounding can effectively prevent interference between parts due to the public impedance of the ground line. The inductance effect of the high-frequency circuit and digital circuit is severe. Single Point Grounding will lead to a longer actual ground line. Therefore, the multi-point grounding and Single Point Grounding should be combined.

2) high-frequency circuits should also consider how to suppress high-frequency radiation noise. The method is as follows: the ground line should be bold as much as possible to reduce the low noise to the ground impedance; a large area (full) grounding, that is, in addition to the transmission signal and the printed line of the power supply, the rest of the copper is fully covered as the ground line, but do not leave useless large area copper foil.

3) the ground wire should form a loop to prevent high-frequency radiation noise, but the ring area should not be too large to avoid generating large induced current. Note that if it is a low frequency circuit, the ground line loop should be avoided.

4) it is best to isolate the digital power supply from the analog power supply, and separate the ground. If there is A/D conversion circuit, it is only possible to stay close to the single point grounding of the device.

1) if it is a low-frequency analog circuit, fill in and shorten the ground line; Single Point Grounding can effectively prevent interference between parts due to the public impedance of the ground line. The inductance effect of the high-frequency circuit and digital circuit is severe. Single Point Grounding will lead to a longer actual ground line. Therefore, the multi-point grounding and Single Point Grounding should be combined.

2) high-frequency circuits should also consider how to suppress high-frequency radiation noise. The method is as follows: the ground line should be bold as much as possible to reduce the low noise to the ground impedance; a large area (full) grounding, that is, in addition to the transmission signal and the printed line of the power supply, the rest of the copper is fully covered as the ground line, but do not leave useless large area copper foil.

3) the ground wire should form a loop to prevent high-frequency radiation noise, but the ring area should not be too large to avoid generating large induced current. Note that if it is a low frequency circuit, the ground line loop should be avoided.

4) it is best to isolate the digital power supply from the analog power supply, and separate the ground. If there is A/D conversion circuit, it is only possible to stay close to the single point grounding of the device.

Analog location and digital location (conversion)

The analog circuit involves weak signals, but the threshold level of the digital circuit is relatively high, which requires less power supply than the analog circuit. In a system with both a digital circuit and a analog circuit, the noise produced by the digital circuit will affect the analog circuit and make the small signal index of the analog circuit worse. The way to overcome this problem is to separately simulate the ground and the digit.
For low-frequency analog circuits, in addition to roughening and shortening ground wires, one point of ground is the best choice to suppress ground interference, it mainly prevents interference between components due to the public impedance of the ground.
For high-frequency circuits and digital circuits, the inductance effect of the ground line will be greater at this time, and a single point of grounding will lead to a longer actual ground line and bring adverse effects, in this case, separate grounding and one point grounding should be used.
In addition, for high-frequency circuits, we also need to consider how to suppress high-frequency radiation noise by adding a ground wire as much as possible to reduce the low noise to the ground impedance; full grounding, that is, in addition to the printed line of the transmission signal, other parts are used as the ground. Do not use large-area copper foil.
The ground line should form a loop to prevent high-frequency radiation noise, but the surrounding area of the loop should not be too large, so as to avoid generating induction current when the instrument is in a strong magnetic field. However, if it is only a low-frequency circuit, the ground loop should be avoided. It is best to isolate the digital power supply from the analog power supply, and separate the ground. If there is a/d, only single point of co-location is here.

Low Frequency does not have much impact, but it is recommended that the simulation and numbers be grounded. When the frequency is high, you can use a magnetic beads to simulate and digitally share the ground.

If the simulated area is directly connected to the digital area, mutual interference will occur. There are four ways to solve this problem: 1. Connect with magnetic beads; 2. Connect with capacitors; 3. Connect with inductor; 4. Connect with a 0 ohm resistor.

The equivalent circuit of the magnetic beads is equivalent to a band-blocking wave limiting device, which can only significantly reduce the noise of a certain frequency point. It is necessary to estimate the noise frequency in advance so as to select an appropriate model. Magnetic beads do not match when the frequency is uncertain or unpredictable.
The capacitor is separated directly, causing float.
The inductance is large in size and has many stray parameters, which is unstable.
0 euro resistance is equivalent to a very narrow current path, which can effectively limit the Loop Current and reduce noise.

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