[The electromagnetism on printed circuit board of summary ] is interfered with mainly power connects up and connects up and produces with the signal. Inhibiting the main method of interference of emerging of connecting up of the power has power level law, ground level law and power bus bar law altogether; The main method of interference of emerging is a distance increased between the lines of signal to inhibit signals and connect up, reduce the distance between line of signal and ground. Meanwhile, design the printed circuit board to also follow certain interference-free principle.
[It is interfered with that keyword ] is electromagnetic; Inhibit
Abstract: Electromagnetic intergerence and suppression of plated circuits panel is mainly produced by the power wiring and the signal wiring.The main methods that produce the disturbance by the suppression of powe r wiring are the power plane law, altogether horizon law and power generatrix law.And the main methods of controlling the disturbance b y the blanketing wiring are to increase the distance of the holding wires and to reduce the distance between the holding wires and ground.At the same time, the design of plated circuit board also should follow certain anti-interference principle.
Key words: printed circuit panel; electromagnetic interference; suppression
The printed circuit board is propping up and holding the part of electronic element in the electronic circuit, it has offered the electric connection between the components and parts in the circuit. As the leap of electronic technology is developed, fast improvement and border of the signal of the logic and clock frequency of system are becoming precipitous constantly in the electronic system especially high-frequency circuit, the electromagnetism produced by this is interfered with usually called the noise More and more outstanding, the interference-free question causes people’s attention more and more. Should begin from primary stage of electronic production to interfere with to inhibit from electromagnetically, made and sets about from the wiring on board of the printed circuit. The wiring on board of the printed circuit is designed, the electromagnetism that should consider reducing the electronic system is interfered with, and also improve the ability against interference of the electronic system, prevent electromagnetic absorption and transmission that interferes with, namely need to accomplish 1 electromagnetic compatible [1 ].
This text mainly discusses the electromagnetism that power connecting up and signal connects up interferes with the question in the wiring design on board of printed circuit. If two wiring design fine, electromagnetic to interfere with, influence one’s own other electronic apparatus or working performance of the system directly, will also make people’s lives and properties threatened when being serious.
Inhibition that a power connects up the electromagnetism of emerging interferes with and interferes with
1.1 The power connects up the electromagnetism of emerging is interfered with
The power will produce distribution capacity, be distributed inductance, distributed resistance while connecting up. Printed circuit supply power at the board power direct current source usually, supply power to offer one accurate voltage for each the intersection of power consuming and components and parts at the the intersection of printed circuit and board in main purpose. And the load that the power drives often has the characteristic of changing in transient state, is distributed the influence of impedance, the load voltage or transient state change in the electric current will be caused the transient state change takes place in the power voltage or electric current, these, like answering the signal source that upper transient state was changed in the intersection of load and end of the power. Especially in high frequency, some devices work in the digital switch state, this phenomenon is more outstanding. In this way the power connects up and not only contain the direct current to press but also contains the voltage that the transient state changes call the parasitic voltage ,Will produce harmonic wave once high to turn into the voltage in wink, it produces the electromagnetic main source [2 ] that interferes with 81-82. When high-frequency, power connect up, can regard as, transmit line [3 ] 41, the intersection of interference and voltage or electric current that power connect up on the some o’clock distribute under the interaction of inductance shaking in distribution capacity, influence the steady work of the circuit.
Employ more switch power to have the advantage of being energy-conserving and high-efficient in the fields of electron, electric apparatus, information at present, the power of switch develops towards high frequency, miniaturization, it is extensive to employ day by day. But the power middle-power of the switch is in charge of working under the high pressure by way of high-frequency switch. High-frequency switch and electric current are close to the square wave, harmonic noise once that contain the abundant one in these square wave signals high. The high-frequency device of the power of switch often produces the spike of the high-frequency high pressure and shakes the wave when open and broken, radiate [2 ] 73 to the space through distribution capacity. The rectification diode working together with power at the same time will produce high frequency to interfere with too, generally relatively close to the power, it is easy to export the line to radiate outwards electromagnetically and interfere with through direct current.
It is the electromagnetic receiver that interferes with that the power connects up at the same time, the outside interference noise will be coupled to the power while connecting up too, through conducting, spread to electronic devices connected.
1.2 Measure of defending the interference that the power connects up
The power can take the following interference-free measure while connecting up:
1.2.1 Power level law
Use one layer on the printed circuit board as the floor of level of power, is one storey as ground level at least, every layer can only offer a kind of power voltage, through crossing the hole and guiding the power voltage to the device on the printed circuit board. This kind of method makes the power connect up and is distributed impedance very low, the circuit is pressed and lowered small, can get the steady direct current and press [2 ] 83 on the device. Lean against very near the levels at the same time, can inhibit the electric field from coupling well. And the round electric current of power level is equal, the magnetic field interferes with being can be offsetted. But this kind of wiring is with high costs, used in the high-speed system more, if takes several kinds of voltage, will need to increase one storey of numbers of level, the cost is higher.
1.2.2 The law of ground level altogether
This piece, publically, high frequency connects up as power and electronic device in the design, the impact on system of return route of the electric current is larger, because of it is the ground of level, power and all signals including sending and receiving The additional impedance which returns to the route is very low, can neglect to lower to press, can receive the steady power voltage on every device. Meanwhile, all power go line and the intersection of signal and line, become mirror image relations with level, electric current that form the intersection of mirror image and electric current too, electromagnetic to interfere with coupling inhibit from well.
1.2.3 Bus bar law of the power
This kind of wiring can offer several kinds of voltage to design separately. The string connecting up is counted and booked through amount of the device. It is slightly bad that this kind of wiring resists than the above-mentioned two kinds of wiring methods electromagnetically and interferes with ability, but the cost is small. This kind of wiring should meet requirements for the following:
1Wiring should be wide.
2Add and decouple capacitively. This kind of electric capacity plays a role in straining the wave in the bypass. Connect greater and smaller straining the wave electric capacity in parallel in the input terminus of the power. When high-frequency, real condenser equivalent to band-pass filter, it for inductance, resistance, capacitive series connection equivalent, larger and smaller electric capacity is used in parallel, the purpose is to increase the bypass and strain the bandwidth of the wave. Meanwhile, will connect a condenser in parallel too between power pin of every active device and ground, the capacity, generally in 0.01 μ F- 0.1 μ F, it is equivalent to a noise wave filter that this connects electric capacity in parallel, can strain the high-frequency harmonic noise [1 ] 89-91.
3The ground wire is surrounded, can vary widely as the ground wire in the bus bar, but the width transition should be smooth, in order to avoid producing the noise, the ground wire should near and supply power in bus bar of power and signal line, because the electric current will produce the inductance of return circuit [2 ] 92 to transmit along the route, the ground wire is neared, the area of return circuit is reduced, inductance quantity is reduced, the impedance of return circuit is reduced, thus it is electromagnetic to reduce and interfere with coupling. Inhibition of interference and interference of emerging that 2 signals connect up
The electromagnetic existence that interferes with must have three conditions, first, electromagnetic interferes with the source, for example: The high-frequency high-power device in the work, second, electromagnetic interfere with sensitive one, third, the electromagnetic spread route that interferes with, for example connect up in signal and the power wiring [1 ] 2, first two kinds of methods that can adopt the shielding, in order to prevent the electromagnetic radiation that interfere with to demanding to realize the electronic product radiating the electromagnetic energy function outwards With absorbing.
Connect up and design and is at the earliest stage that printed circuit board makes, the electromagnetic and compatible degree of freedom incorporated at this moment is largest, the lowest cost taken, must fully consider its electromagnetic compatible performance. The signal connects up and is distributed inductance, distribution capacity and distributed resistance too, they have represented interference couple the distribution parameter of the route, the is distributed the parameter and increased with increase of frequency of signal.
So long as there is difference of electric potential, the electric field that two pieces of space will exist in two lines. Suppose three pieces of wire, A, B are the line of signal respectively, D is the ground wire, C AD is the distribution capacity of A, if the electric potential of A is higher than that of B, B is in some or some,etc. surfaces of location of A, will coupling take place with B in the electric potential in A, this kind of electric field couples to holding coupling. The same B and A may produce this kind of coupling. Inhibit the holding method to couple: First, increase by two distance greater than 1/4 of the largest wavelength of the interfering signal connecting up between the wire 9,Second, reduce the distance between line of signal and ground.
If A, B two wire near, when having electric current in the wire A, have a magnetic field around it, magnetic the intersection of sense and line have a part around get the intersection of conductor and return circuit that B makes up, B return circuit produced and induce currents by reaction, this kind of magnetic field interferes with coupling to belong to interfering with perceptually mutual inductance Coupling. Meanwhile, if the intersection of A and electric current in the wire change, will store self inductance in, even can produce and interfere with perceptually self inductance Coupling. Inhibit interfering with the coupling method perceptually: First, increase the distance between line of signal and signal line, in order to reduce the mutual inductance, the reason is in inverse proportion to distance [4 ] 224 of mutual inductance coefficient. Second, reduce the distance between line of signal and ground, in order to reduce the coherent area of magnetism enclosed between line of signal and ground. Reduce line from outside, should try hard, prevent the intersection of signal and line from lay parallelly.
Also have other interference on the printed circuit board, such as the temperature noise.
3 printed circuit board resists in consideration electromagnetically and interferes with the principle that the respect should be followed
3.1 Consider the size of the whole circuit board at first, does not use the printed circuit board larger than the actual need [2 ] 75.
3.2 Unit circuit such as digital circuit and simulation circuit, high frequency and low frequency of different functions Set up separately, connect up figure should easy signal circulate and make signal flow into as as possible keeping unanimity.
3.3 Print the wire as much as possible short and wide. Its minimum width should be by bearing the size it is generally 2 of the specified electric current of the electric current- 3 times And fix, but the minimum width is unsuitable to be smaller than 0.2 mm. In printing the circuit of high density, high precision, the width desirable 0.3 mm as interval of the wire, it is 2 mm [1 ] 211 that the ground wire is minimum in width. Print turning round and should become the round angle of wire, the wire on board of per layer of circuit should be each other vertical, oblique to hand in ,It is parallel to one another to avoid.
3.4 Use and shield and strain the wave technology, the segregation while noticing level pigeonholing rationally.
3.5 The exertion of the component, try not to select for use than the component with faster speed of the actual need, in arranging in the position of the component, it is easy to be can’t be apart too near the electromagnetic components and parts that interfere with, should be greater than 1/4 of the signal wavelength, input the device and exports the device and try hard to be far away from.
3.6 Make sure to ground safely. Circuit of low frequency under 1 MHz Can be by clicking and linking the ground only. The type of place connected can make whom every electric current of circuit produce flow through wire, press, lower, influence each other, will form interference, but the type of place received to complicated for system to realize, stand up very much troublesome. A commonly used one to connect single some earthing in series, but every electric current of circuit flow through a public impedance in the way this, every circuit connect what place produce press, lower, can lead to the fact the interference at various degrees to all circuit. High-frequency circuit above 10 MHz Must adopt the multipoint earthing [2 ] 68-70, [5 ] 140. A complicated electronic system will be stored in the ground of power, signal and shield the ground, should receive them on the public ground wire.
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