01
What is the principle of 20h?
The principle of 20h is to refer to the distance between the power layer relative to the formation of 20h, and h indicates the distance between the power layer and the formation.
Of course, it is also to suppress the edge radiation effect. Electromagnetic interference is radiated outward on the edge of the board. The power layer is contracted so that the electric field is only conducted within the range of the ground layer, and EMC is effectively improved. If the inner zone is 20h, 70% of the electric field can be limited to the ground edge; the contraced 100h can be limited to 98% electric field.
We require that the ground plane is greater than the power supply or signal layer, which facilitates preventing external radiation interference and shielding the external interference. In general, the power supply layer is substantially more than 1mm in the formation of the formation when the PCB is designed. The principle of 20h can be satisfied.
02
How to reflect 3W principles and 20h principles in the PCB design?
First, 3W principle, it is easy to manifest in the PCB design, ensuring that the central spacing of the trace and the trace is 3 times, such as the line width of 6 mils.
So in order to meet the principle of 3W, the rule of the Allegro set line to the line can be 12mil, the spacing in the software is calculated the spacing of the side, as shown:
3W principle diagram in PCB
Second, 20h principle, when the PCB is designed, in order to embody the principle of 20h, we generally shrink 1mm than the formation when the plane is divided.
Then on the 1 mm inner ribbon, the via hole is hosted, 150mil, as shown in the figure:
Schematic diagram of 20h in PCB
03
Which types are divided into signal lines in the PCB?
The signal line in the PCB is divided into two, one is a microstrip line, one is a strip line.
The microstrip line is a strip-shaped trace that walks on the surface layer (Microstrip), as shown in the figure below, the blue portion is a conductor, the green part is the insulation of the PCB, the blue small piece above Microstrip Line. Since the Microstrip Line is exposed inside the air, radiation can be formed around or is attached to the surrounding radiation interference, and the other side is attached to the insulation dielectric of the PCB, so it formed by the electric field is distributed in the air, the other Distributed in the insulation medium of the PCB. However, the signal transmission speed in Microstrip Line is fast than the signal transmission speed in the Stripline (strip line), which is the advantage of its prominent.
Table micropipe line diagram
Tape line: Stripline / Double Stripline, built-in trace bury inside the PCB, as shown in the figure below, the blue part is the conductor, the green part is the insulation electrical medium of the PCB, Stripline is embedded in two layers The strip wire between the conductors. Since Stripline is embedded between two layers of conductors, its electric field distribution is between two packages therebetween, which does not radiate out energy, nor is it affected by external radiation interference. However, due to its surrounding dielectric (dielectric constant ratio 1), the transmission speed in Stripline is slower than in Microstrip Line.
Tape line diagram
04
What is EMC?
EMC, is an abbreviation of Electro Magnetic Compatibility, translation is electromagnetic compatibility, refers to the ability to function properly in its electromagnetic environment and does not constitute anything in the environment that cannot withstand electromagnetic harassment.
Sensor electromagnetic compatibility refers to the adaptability of the sensor in an electromagnetic environment, maintains its inherent performance, and completes the ability to complete the predetermined function. It contains two aspects: one aspect requires that the sensor generates electromagnetic interference to the environment during normal operation; on the other hand, the sensor requires that the sensor has a certain degree of electromagnetic interference in the environment has a certain degree of immunity.
05
What are the design methods of simulated and digitally in PCB design?
Generally processing simulated grounds, the method of digitally has the following:
Directly separate, connect the digital area to DGND in the schematic, the analog area is connected to AGND, and then the planes in the PCB are divided into digitally and simulated grounds, and the spacing is large;
Digitally uses a magnetic bead connection between the simulated ground;
Digitally use capacitance connection between digitally and simulated grounds to use capacitive intercepting.
Digitally use inductively connected between the simulated ground, the sense value from UH to tens of UHs.
Digitally connects between zero ohm resistors between the simulated ground.
In summary, the capacitor is interposed straight, causing floating ground. Capacitor is not straightflite, which causes pressure differential and static accumulation, and hick. If the capacitance and the magnetic bead are parallel, it is to draw a snake, because the magnetic bead is general, the capacitor will be invalid. If you are in series, you will seek.
The inductance is large, the spurious parameters are more, the characteristics are unstable, and the discrete distribution parameters are not well controlled, and the volume is large. Inductors are also trap, LC resonance (distributed capacitance), there is special effects on noise.
The equivalent circuit of the magnetic bead is equivalent to the strip block, only the noise of a certain frequency point, if noise, how to select a model, and the noise frequency is not fixed, so the magnetic bead is not a good s Choice.
The 0 Euro resistor is equivalent to a very narrow current path, which can effectively limit the loop current to suppress noise. The resistor has attenuation effect on all frequency bands (0 Euro resistors also have impedances), which is stronger than the beads.
In short, the key is to simulate and digitically. It is recommended to use 0 Euro resistors between different types; the power supply is introduced into the high frequency device; the high frequency signal line coupling small capacitance is used; inductance is used in high power low frequency. Read the full article, original title: PCB common five major design problems, have you encountered?
Article Source: [Micro Signal: FCSDE-SH, WeChat Public Number: Semiconductor PDSA] Welcome to add attention! Please indicate the source of the article.
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