Getting Electronics Engineers: treasure does not pass the PCB layout

REVIEW electronic design engineers can not do without electronic circuit PCB layout, it is an important part of the PCB design process, innervation, like it is like the human body, often a small problem can lead to other parts of the body obstacles. Electronic pcb circuit wiring, too, so there are many areas in which we need to pay attention to, the following I will share some of the details of the main bar.
A circuit board design steps
Generally, circuit board design process can be divided into three basic steps.
(1) schematic circuit design: the schematic circuit design mainly PROTEL099 schematic design system (Advanced Schematic) to draw a circuit diagram. In this process, to take full advantage of various drawing tools PROTEL99 schematics provided by a variety of editing functions to achieve our objective, namely to get a proper, beautiful circuit schematic.
(2) generating netlist: shows a network bridge between the circuit schematic design (SCH) and the design of the printed circuit board (PCB), which is the soul of the board automatically. Netlist can be obtained from the circuit diagram may also be extracted from the printed circuit board.
(3) printed circuit board design: the printed circuit board is designed primarily for the purposes of another important part of the PCB PROTEL99, in the process, we use the power of PROTEL99 implementation provided by the layout of the circuit board complete the difficult work.
Second, the drawing simple circuit diagram showing
schematic design schematic of the design procedure is accomplished according to the following:
(1) the size of the design drawings Protel99 / Schematic, a good idea to first part drawing, good design sheet size. Sheet size is based on the size and complexity of circuit diagrams may be, set the appropriate paper size is a good first step in designing schematics.
(2) Set Protel 99 / Schematic design environment provided Protel 99 / Schematic design environment, includes a grid size and type, cursor type, etc., most of the parameters may also use the system default value.
(3) The user needs a circuit diagram of the rotating part and the part removed from the part library is placed onto the sheet, and the number of parts, the parts are placed the package definition and setting work.
(4) wiring schematics using various tools Protel 99 / Schematic provided on the drawing element having electrical connecting wires meaning, symbols, to form a complete schematic.
(5) draw a good preliminary regulating circuit a circuit diagram for further adjustments and modifications, such schematics more beautiful.
Various reporting tools (6) provided by the report output Protel 99 / Schematic generate various reports, the report is the most important network table, the subsequent circuit board design to prepare the network table.
(7) file is saved and the final step is to print the output file to save and print output.
Principle of Single-chip panel design principles to be followed are as follows:
(1) in the layout of components, elements should be related to each other as possible put too recently, for example, a clock generator, crystal oscillator, a clock input terminal of the CPU are easy to produce noise, when they should be placed closer. For those devices, a small current circuit, a large current circuit switching circuit is easy to produce noise, should make the logic control circuit and a memory circuit (ROM, RAM) remote from the microcontroller, if possible, wheat | Si | Ai | Tim | P | CB | template | patch | Michael | Sri Lanka | Ai | Farm | Section | technology | National | first P | CB model playing board. These additional circuits can be formed a circuit board, it is a good anti-interference, improve the circuit resistance.
(2) as far as a key element, such as a next chip ROM, RAM and the like mounted decoupling capacitors. In practice, printed circuit board traces, wires and connection pins and so may contain a large inductance effect. High inductance traces may cause serious switching noise spikes at Vcc. The only way to prevent the line switching noise spikes go Vcc, is placed between the electron 0.1uF a VCC power supply decoupling capacitors. If the circuit board using surface mount components, can be used directly bear chip capacitor * the element fixed to the Vcc pin. Is best to use ceramic capacitors, since such capacitor has a low static dissipative (ESL) and high-frequency impedance and the stability of the medium on the temperature and time of this capacitor is also very good. Try not to use tantalum capacitors, because of its high impedance at high frequencies. When mounting the decoupling capacitors to note the following:　
the power input side printed circuit board jumper around electrolytic capacitor 100uF, if the volume of permitting, a number of large capacity is better. Next to each integrated circuit chip requires a 0.01uF ceramic capacitor is placed in principle, if the gap is too small the circuit board is placed high, about every 10 chips can be placed a tantalum capacitor having 1 to 10. For the anti-interference ability is weak, the large off current change element and RAM, ROM and other storage element, should the power supply line (Vcc) and ground access between decoupling capacitors. Lead capacitance not too long, especially not with high frequency bypass capacitor leads.
(3) in the microcomputer system, there are many types of ground, systematic, shield, logically, analog, etc., whether ground reasonable layout, will determine the ability of anti-jamming circuit board. In the design of ground and ground, you should consider the following questions:
Logic and analog ground to separate the wiring, can not be combined, their respective ground line connected to a respective power supply ground, respectively. In the design, analog ground should be bold, and try to increase the ground contact area of terminations. Generally, for analog signals between the input and output of the microcontroller circuit is preferably isolated by an optocoupler. When the printed circuit board design of a logic circuit, which forms a closed loop ground should improve circuit's noise immunity. Ground should be coarse. If the ground is very small, then the ground resistance will be large, resulting in a change in current with the ground potential vary, resulting in signal level is unstable, resulting in decreased circuit's noise immunity. In the case where the wiring space permitting, to ensure that at least the width of the main ground line 2 ~ 3mm or more, the ground line on the pin member should be about 1.5mm.
Third, power, ground handling
Although the entire PCB wiring board have done well, but still need to take into account the interference power, ground caused, this will reduce the performance of the product, and even affect the success rate of the product. So for power, ground wiring to be taken seriously, the interference power, ground generated to a minimum, ensure product quality.
Each product in the electronic design engineers understand why the interference between the power line and the ground, is only to reduce interference suppression type to make statements.
To add decoupling capacitor between the power supply and ground.
Try to widen the power and ground, preferably ground than the power supply line width, the relationship is: Ground> power cables> signal line. Normally a signal line width: 0.2 ~ 0.3mm, the smallest width of up to 0.05 ~ 0.07mm, the power cord is 1.2 ~ 2.5mm.
PCB digital circuit design available to the wires that comprise a wide loop, constituting a network to be used, but can not remember the analog circuits used as such. Large area of the copper layer as the ground, the place is not in use are connected to ground on the printed circuit board, made of plywood or used as a ground, power, ground occupied by each layer.
Four were treated in the digital and analog circuits
are now, no longer a single PCB many functions of the circuit, but a mixture constituted by a digital circuit and an analog circuit, when the wiring need to consider the mutual interference between them problems, especially noise interference line.
High frequency digital circuit, analog circuit sensitivity strong, the signal line, the high-frequency signal line away from the sensitive analog circuit device as much as possible, and to ground, the junction of the entire PCB outside only a, it is necessary to issue No. PCB internal processing digital circuit and analog circuit common ground, in the internal circuit board, the ground digital and analog circuits are physically separate circuits, but at the interface with the outside is connected to PCB (e.g., plugs, etc.). And analog to digital circuit ground is a little short circuit, note that only one connection point, there are no common ground on the PCB, which is determined by the system designer.
V. signal line cloth on the power (ground) layer
in the multilayer printed wiring, since the signal line layer fabric finish line did not have much left, and then more layers will result in waste, will increase the workload and costs may be considered for the electrical wiring (earth) layer, first consider a power source layer, followed by the formation, as can best retain the integrity of the formation.