PCB design is required for all electrical engineers, and want to design a perfect piece of PCB and not look so easy.A perfect piece of PCB components selection and set up reasonable, not only have to do also need to have good signal transmission performance.This article will just PCB wiring technique of high-speed signal circuit design knowledge, a detailed introduction and sharing, hope to be able to help you work.
Reasonable use a multilayer PCB wiring
In the actual design process of PCB, most will choose to use a multilayer of engineers to carry out high speed signal wiring work, this kind of sandwich plate is indispensable part, is also help engineers is the effective means to reduce the interference of the circuit.In high-speed signal by using sandwich plate to complete the PCB circuit design, the engineer need reasonable choice layer to reduce the PCB size, make full use of the middle layer to set the shielding, implement nearby ground, can effectively reduce the parasitic inductance, shorten the length of signal transmission and reduce the cross interference between signals and so on, all of these methods on the reliability of the high speed circuit is very beneficial.
In addition to the above mentioned several use multilayer PCB reliability of signal transmission, and part of the authority, according to the same material 4 layer board than double panel of 20 db noise is low.Wire bending has been jumped over lesser, had better use the straight line, need to turn, line or the circular arc turning 45 degrees are available, and can reduce the foreign high speed signal transmission and mutual coupling, to reduce the radiation and reflection signals.
High-speed circuits between pin leads as short as possible
On PCB in the process of the design of high-speed signal circuit and wiring, engineers need to be as much as possible to shorten the high-speed circuits between pin lead, thought that the longer the lead, the stray inductance and capacitance value, the greater the reflection, this will result in high speed circuit system oscillation, etc.
In addition to as much as possible to shorten the high-speed circuit components between pin, lead in the process of PCB wiring, the high-speed circuits between pin wire layers alternating between the less the better, is used in the process of elements are connected via the less the better.Generally speaking, a through hole can bring about 0.5 pF distributed capacitance, which will result in delay of the circuit.High-speed circuit wiring should pay attention to at the same time, introduced by signal walk close parallel lines "cross interference", if cannot avoid parallel distribution, can decorate a large area on the opposite side of the parallel line "to" to reduce the interference.In the adjacent two layers, go line be sure to take for perpendicular direction.
For the signal lines or local units is particularly important ground surrounded
On PCB layout design process, engineers can is very important for some signal lines using the method of ground surrounded, can be in such as the clock signal, high-speed analog signals such as less susceptible to interference signals go line in peripheral plus protection with the ground, will be caught in the middle line of protection.Because in the process of design, all kinds of signal line can't form a loop, same ground also cannot form current loop.And if the cloth line produce loop circuit will produce very big interference in the system.Surrounded by using ground signal wiring method, can effectively avoid wiring formed when the loop.Should be near each integrated circuit block set one or several high frequency decoupling electric capacity.Analog ground and digital ground to the ground with high frequency link of choke.Some high speed signal lines should be special treatment: differential signal requirements as near to the parallel on the same layer and walk the line, difference between signal lines are not allowed to insert any signal, and required length.
In addition to several design methods mentioned above, the signal wiring for PCB design, the engineer should also avoid high-speed signal wiring nodule formation or stump.High-frequency signal lines on the surface easy to generate larger electromagnetic radiation, the high frequency signal wiring between power supply and ground, through the power and the bottom to absorb electromagnetic waves, generated by the radiation will be reduced a lot.