PCB desgin and PCB layout knowledge

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PCB desgin and PCB layout knowledge <span class="sdata2" title="2017-10-05T07:22:30+00:00"></span>

PCB desgin and PCB layout knowledge tips

The choice of PCB board must meet the design requirements and the production volume and cost to achieve a balance.

The design requirements include electrical and institutional parts.

This material problem is usually important when designing very high speed PCB boards (frequencies greater than GHz).

For example, the commonly used FR-4 material, dielectric loss at several GHz frequencies, can have a significant effect on signal attenuation and may not be used. In the case of electrical, it is important to note whether the dielectric constant and the dielectric loss are combined at the designed frequency.

pcb raw material

The basic idea to avoid high-frequency interference is to minimize the interference of
the high-frequency signal electromagnetic field, that is, the so-called crosstalk .

Can be used to pull the high-speed signal and the distance between the analog signal,
or ground guard / shunt traces next to the analog signal.

Also pay attention to the digital ground to the analog ground noise interference.

high frequency interference

Signal integrity is essentially a problem of impedance matching.

The factors that affect the impedance matching are the architecture of the signal source and the output impedance, the characteristic impedance of the trace, the characteristics of the load side, the topology architecture, and so on.

The solution is * termination and alignment of the topology

signal integrity

Differential pairs of line have two points to note,
One is the length of the two lines to the same length,
The other is the distance between the two lines (this distance determined by the differential impedance) to remain the same,

That is, to keep parallel.There are two parallel ways, one for the two lines walking in the same line layer (side-by-side),

one for the two lines in the upper and lower adjacent two layers (over-under).

Generally in front of the side-by-side to achieve more ways.

difference impedance line

It is necessary to use differential wiring is the signal source and the receiver are also differential signal meaningful.

So for only one output of the clock signal is unable to use the differential wiring.

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