pcb设计经典技巧PCBclassicdesignskills.doc

pcb 设计经典技巧(PCB classic design skills)This paper consists of 544852010 contributionsDOC documents may experience poor browsing on the WAP side. It is recommended that you first select TXT, or download the source file to the local view.PCB design experience skills, LED current up to dozens of mA, with the LED current lead length and path extension, LED ON/OFF often become peripheral powerOneThe cause of noise (switching). Therefore, the drive transistor must be as close as possible to the LED in packaging so as to reduce the flow path of the LED current IC. The luminance of LED is proportional to the drive current. Generally, green LED is used as a benchmark. 2. How to avoid high frequency interference? The basic idea of avoiding high frequency interference is to minimize the interference of high frequency signal electromagnetic fields, which is called crosstalk (Crosstalk). The distance between the high speed signal and the analog signal can be pulled up, or the ground guard/shunt traces is added beside the analog signal. Also pay attention to the noise jamming to the analog ground digitally. 4, how is the differential distribution pattern implemented? There are two points in the routing of differential pairs. One is that the lengths of the two lines should be as long as possible, and the other is the spacing of the two lines (which are determined by differential impedances), which is to remain the same, that is, to keep parallel. There are two parallel ways, one for the two lines, the same on the line (side-by-side), one for the two lines, and two for the upper and lower levels (over-under). In general, side-by-side implemented more ways. 6. Can a matching resistor be added to the difference line between the receiver and the receiver? The matching resistance between the differential lines of the receiving end is usually added, and the value should be equal to the value of the differential impedance. The signal quality will be better. The routing of differential pairs should be close and parallel. 8. How do you deal with some theoretical conflicts in actual wiring? 1. basically, it is right to divide modules / numbers into isolation. It should be noted that the signal should not be crossed as far as possible in the moat, and do not let the current return of the power and signal (returning, current, path) become too large. The 2. oscillator is the positive feedback oscillation circuit simulation, have stable oscillation signal, gain and loop must meet the phase specification, and the specification of this oscillation analog signal is vulnerable to interference, even with the ground guard traces may not be completely isolated interference. And too far away, the noise on the ground plane will also affect the positive feedback oscillation circuit. So make sure that the distance between the crystal and the chip is near. 3. , there is a lot of conflict between high-speed wiring and EMI requirements. But the basic principle is that, because of the resistor, capacitor or ferrite bead added by EMI, some electrical characteristics of the signal can not be met. Therefore, it is better to solve the problem of EMI by arranging the routing and PCB stacking techniques, such as high-speed signals coming in the inner layer. Finally, resistors, capacitors, or ferrite bead are used to reduce the damage to the signal. 9, how to solve the contradiction between manual routing and automatic routing of high speed signals? At present, most of the automatic cabling devices with strong cabling software have set constraints to control the winding mode and the number of vias.Each EDA company's winding engine capabilities and constraints setting projects sometimes differ greatly. For example, if there is enough hunting line control constraints (serpentine) winding, the ability to control the differential pair line spacing. This can affect the way the wiring automatically comes in line with the designer，s idea. In addition, manual adjustment of the ease of routing is also absolutely related to the ability of the winding engine. For example, the pushing capacity of the line, the ability to push through the hole, and even the pushing capacity of the wire to copper. So, it's a solution to choose a router that has a good ability to do the winding engine. 11. In the high-speed PCB design, the blank area of the signal layer can be deposited with copper. How should the copper layers in the signal layer be allocated on the ground and the power supply? Most of the copper deposited in the blank area is grounded. Only when the copper is deposited near the high speed signal line, the distance between the deposited copper and the signal wire should be paid attention to, because the copper deposited will reduce the characteristic impedance of the wire. Also be careful not to affect the characteristic impedance of its layer, for example, in the structure of dual stripline. 12, can you use the microstrip line model to calculate the characteri。