PCB Layout summary

PCB Layout As part of the hardware design, but also a very important aspect; in the case of hardware circuit design reasonable, in fact, he is an absolute important indicator affecting performance. Now many PCB Layout constraint rules are in accordance with the hardware engineers or engineers PI SI engineer to complete the layout analysis, which is commonly known as
"wire drawing stations." They mechanically repeating a block PCB design is completed, after a period of time to design, some of them may already have some experience with this: What do equal length, which leave a crude, which should be parallel to ensure proper line spacing, etc. Wait.
However, they are based on the so-called experience, that know not why. I think, in order in such a highly competitive society to survive, then a breakthrough, then it is necessary to broaden their knowledge. That is, PCB Layout
Engineer can not let people see themselves as "pull station" to look at. That first of all, you have to have a certain ability to understand the circuit (of course, as hardware engineers that design ability is not necessary, if they can, it is best); secondly, you need the SI / PI engineer for PI / SI capability analysis (of course, need We have the ability to RF simulation is not necessary, if they can, it is best). After possess this knowledge, you will not only have a good PCB design capability, and also hardware, SI / PI engineers theory of capital, they can even give advice circuit design from the PCB design.
Ado, summarize some of the principles from some of the PCB design, experts hope to be able to correct errata.
First, on the layout of
explanation 1 layout, literally, is to place the circuit elements reasonable. That kind of how the placement is reasonable, a simple modular principle is divided into clear, that there are certain basic circuit of people, you get a piece of the PCB will be able to see what is used to implement functions.
2. The specific design steps: First, a schematic diagram of generating an initial document PCB, PCB layout completion of the pre-determined area of a PCB Layout opposite, then tell structure, we give the structure of the area, and the structure of the overall design , give a specific constraint.
The side restraint panel structure is completed, positioning the mouth and some keepout drawing, and then placing the connector is completed.
4. Principle of display elements: the master MCU is generally placed in the center of the board, and then placed adjacent to the joint interface circuit (such as network interface, USB, VGA, etc.), and most interfaces have further ESD protection there filtering process. Follow the principle of protection after the first filter.
5. Then the power module is generally placed at the main power supply at the power entry module (such as system 5V), a separate power supply module (such as module circuit powering 2.5V) may be placed in the same power network-intensive areas according to the actual situation.
6. Some internal circuit, not lead to the connector. We generally follow such a basic principle: high, low subregion, analog, digital sub-region, the source of interference, receptors sensitive subregions.
For a single circuit module 7. Then, the follow current flows when the circuit design to design.
The overall layout of the circuit, is probably the case, welcome to the great God to supplement and correct me.
Second, on the wiring
1. wiring, the basic requirement is to ensure effective communication with all network connectivity is very easy to do, effective and is a relatively vague concept. In fact, nothing less than two kinds of signal in the digital circuit and analog signals, digital circuit, it is to ensure a sufficient noise margin, the analog signal, the zero-loss as far as possible.
2. A pre-wiring, generally had to understand the design of PCB laminate, i.e., all of the wiring layer planning: optimum wiring layer, the wiring layer suboptimal. . . . Optimal wiring layer, which is adjacent to the ground plane full interview, which layer we generally used cloth important signal (including all signals, differential signals, analog signals in DDR, etc.). Other signals (I2C, UART, SPI, GPIO ) take other layers, and to ensure that there is only important in this region the correlation signal circuit (such as DDR, network interface, etc.)
3. Then consider the reflected high-speed signal wiring, crosstalk, the EMC and so on, it is generally impedance matching needs to be done, such as single line 50R, the differential line 100R and the like, particularly subject to the actual design (equal to the impedance principle is to ensure continuous), the main consideration crosstalk 3W / 2W principle, package handling and the like.
4. The power supply and the power circuit, first to ensure adequate load capacity, i.e. the power of the whole refluxed Road King short and thick as possible, from the called EMC point of view, the loop reflux, to form a loop antenna, external radiation, do so possible to reduce the loop area.
PCB layout summary of
the overall circuit wiring, is probably the case, welcome to the great God to supplement and correct me.
Third, with regard to
1. and ground design is a very important part in the PCB design, since as an important reference plane, a problem if the ground plane design, stability is no way other signals. Out here alone, talk about their own personal opinions.
2. We divided the general system and chassis ground, the chassis ground product name suggests is connected to the sheet metal, the system as a reference plane i.e. the entire circuit system.
3. The general principles of the systematic and practical housing are: system chassis ground and divided, and multipoint connection system or by magnetic beads and a single point of high voltage capacitors.
4. With regard to the system: divided digitally, analog, power from the function. About the sub-division has been controversial, I am here to represent the personal views. First, the case of the layout is very reasonable, I think it can not be divided. What layout is very reasonable, that is, digital area only digital signals, analog area only analog signals, power signals only regional power, and there is a complete ground plane underneath them. Since the current and water are similar in that they both go with the flow, because they are present below the complete ground plane, from the shortest, lowest principle, they are directly under reflux, without he went to other places to go. However, sometimes, not so good, there are some cross-regional, this time selecting a single point is generally understood that the use 0R resistor (beads not recommended, because the high-frequency, magnetic beads have filtering effect). Close placement of cross-resistance where the most intensive, the smallest area will flow.
These are summed up in my work, some knowledge, may vary in detail, even the existence of flaws, but also in big trouble God correct,
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