Printed circuit board (PCB) wiring has crucial effect in high speed circuit, but it often is circuit design process is final one of a few measure. Wiring of high speed PCB has the problem of a lot of respects, about this title already somebody compose many document. The article basically discusses the wiring issue of high speed circuit from the angle of practice.

 

 

If not be yourself design wiring, must the design of the person of time microscope wiring with abundant put apart. Touch in this very small precaution on the dot of on 100 times remedy. The person that does not count on wiring can understand your think of a way. In the initial stage of wiring design process your opinion is mixed guidance is the most important.

 

The information that you can provide is more, and you intervene in whole wiring process more, the PCB that gets as a result can have been jumped over. The wiring progress report that designs an engineer to install a —— of provisional the dot that finish to want according to you to wiring is checked quickly. This kind of “ closes method of annulus road ” can prevent wiring go astray, fall the possibility of do poorly done work over again thereby to lowest.
 

The brief characterization of circuit function?

Indicate to input and output PCB delineation of the position?

PCB cascade information?

Do each need those signal?

Is the demand significant of component set the position?

Does bypass component cut the position really?

It what print a line is very important that what print a line?

What circuitry needs to control impedance to print a line?

What circuitry needs to match the size of length; component?

What print a line to need each other to be far from (or stand by) ?

What circuitry needs each other to be far from (or stand by) ?

Need of yuan of what parts of an apparatus each other are far from (or stand by) ?

Yuan of what parts of an apparatus should be put in PCB above, what is put below?

 

Do not complain the information that needs others is too much forever. Too little? Yes. Too much? Not.

 

 

Positive-appearing image is in PCB, the position decides everything. Put a circuit in the what position on PCB, its specific circuit element installation is in what position, and what is the other circuit of its photograph adjacent, all these is very important.

 

Normally, the position of input, output and power source is predefine is good, but the circuit between them develops respective creativity ” with respect to need “ . Why do this notice wiring details will emerge the account of tremendous redound namely. From the positional proceed with of crucial element, will consider according to specific circuit and whole PCB. Conduce to from the method of the place that provides crucial element at the beginning and signal ensure the design achieves expectant working goal. Get proper design can reduce cost and pressure —— to also shorten development cycle.

 

 

Alleged parasitism effect is those sneak away to enter your PCB and be applied greatly in circuit destroy, have a headache the little trouble that makes person, reason unidentified (according to literal meaning) . They are capacitance of parasitism of the hidden in circuit of infiltration high speed and parasitism inductance.

 

Include among them by enclose bring foot and print a line to grow solder of formation parasitism inductance; too dish to the ground, solder dish to power source plane and solder dish to print the mutual influence between the via of parasitism capacitance; that forms between the line, and the parasitism effect with a lot of potential other. Graph 1(a) shows the picture of principle of inphase operation amplifier that gave a typical case. But, if consider parasitism effect, same circuit may turn a graph into 1(b) in that way.

 

Graph 1. Typical operation amplifier circuit,

(A) former blueprint, (B) considers the plan after parasitism effect

 

In high speed circuit, very little value can affect the performance of circuit. Occasionally law of a few skins (the electric capacity of PF) is sufficient. If parasitism electric capacity is sufficient old saying, what it can cause circuit is not stable with oscillation.

 

When seeking the parasitism cause that has a problem, find sth useful calculates the possibility a few times afore-mentioned basic formula of those parasitism capacitance dimension. Formulary (the formula that 1) is capacitor of computational parallel plate.

 

 

Formulary (in 1) : C states capacitance is worth, a expresses to be the plate area of the unit with Cm2, k expresses the opposite dielectric constant of PCB material, d states the plate span that is an unit with Cm leaves.

 

Banding the parasitism effect that inductance is consideration of additionally one kind of need, because print what the line grows too or plane of devoid ground connection causes,it is. Formulary (2) is computation prints line inductance (the formula of Inductance) .

 

 

Formulary (in 2) : W expresses to print line width, l expresses to print line length, h expresses to print the ply of the line. Full measure is an unit with Mm.

 

Graph the effect that 2 medium oscillation show those who gave amplifier of high speed operation to input upright length to be 2.54cm in phase to print a line. Inductance of its equivalent parasitism is 29nH(10-9H) , enough causes persistent low-pressure oscillation, can answer cycle to whole transient state continuously. Graph 7 still show the effect that gave how to use ground connection plane to reduce parasitism inductance.

 

Graph 2. Ground connection plane and planar without ground connection pulse are answered

 

Via is source of additionally one kind of parasitism, they can cause parasitism inductance and parasitism capacitance. Formulary (the formula that 3) is computational parasitism inductance.

 

 

Formulary (in 3) : T expresses the ply of PCB, d expresses to be the via diameter of the unit with Cm.

 

Formulary (4) is how to be calculated the formula that the parasitism capacitance that via causes is worth.

 

 

Formulary (in 4) : εr expresses the opposite magnetism conductance of PCB material, t expresses the ply of PCB, d1 expresses to surround the solder of via dish diameter, d2 expresses the diameter of the clearance hole in ground connection plane, all dimension all are an unit with Cm.

 

In a 0.157cm a via can increase the parasitism electric capacity of the parasitism inductance of 1.2nH and 0.5pF. This is the account that why must always maintain guard when giving PCB wiring, want to will send the influence of unripe effect to fall to the smallest.