CNSMT Custom Wifi Router SMD LED PCB Board Electronic Circuit Board
|Product Name:||SMD LED PCB Board|
|Used for:||SMT FACTORY Electronic Circuit Board|
|Our Main Market||Whole of the world|
The design of the printed circuit board is based on the circuit
schematic and implements the functions required by the circuit
designer. The design of the printed circuit board mainly refers to
the layout design, and the layout of the external connection needs
to be considered. The optimal layout of internal electronic
components. Metal wiring and through hole optimization layout.
Electromagnetic protection. Heat dissipation and other factors.
Excellent layout design can save production costs and achieve good
circuit performance and thermal performance. Simple layout designs
can be implemented manually, and complex layout designs require
computer-aided design (CAD).
In high-speed designs, the characteristic impedance of controlled
impedance boards and lines is one of the most important and common
problems. First understand the definition of the transmission line:
The transmission line consists of two conductors of a certain
length, one conductor is used to send signals, and the other is
used to receive signals (remember the notion of "circuit" instead
of "ground"). In a multilayer board, each line is part of a
transmission line, and the adjacent reference plane can be used as
a second line or loop. A line a "good performance" it is critical
transmission line characteristic impedance of the entire circuit
remains constant. 
The key to the circuit board being a "controlled impedance board"
is to make the characteristic impedance of all lines meet a
specified value, usually between 25 ohms and 70 ohms. In a
multilayer circuit board, the key to good performance of the
transmission line is to keep its characteristic impedance constant
throughout the entire line.
But what exactly is characteristic impedance? The easiest way to
understand the characteristic impedance is to see what the signal
encounters during transmission. When moving along a transmission
line with the same cross-section, this is similar to the microwave
transmission shown in FIG. Assume that a step voltage of 1 volt is
applied to this transmission line, such as a 1 volt battery
connected to the front end of the transmission line (it is located
between the transmission line and the return line). Once connected,
this voltage wave signal follows the line at the speed of light.
Spread, its speed is usually about 6 inches/nanoseconds. Of course,
this signal is indeed the voltage difference between the
transmission line and the loop, which can be measured from any
point on the transmission line and the point of the loop. FIG. 2 is
a schematic diagram of the transmission of the voltage signal.
Zen's method is to "generate a signal" first, and then spread along
this line at a speed of 6 inches/nanoseconds. The first 0.01 ns
advances by 0.06 inches. At this time, the sending line has an
extra positive charge, and the circuit has an extra negative
charge. It is these two kinds of charge differences that maintain a
voltage difference of 1 volt between the two conductors. The two
conductors form a capacitor.
In the next 0.01 nanosecond, the voltage of a 0.06 inch
transmission line is also adjusted from 0 to 1 volt, which must add
some positive charge to the transmission line and add some negative
charge to the receiving line. For every 0.06 inches of movement,
more positive charge must be added to the transmission line, and
more negative charge must be added to the circuit. Every 0.01
nanosecond, another section of the transmission line must be
charged and then the signal begins to propagate along this section.
The charge comes from the battery at the front end of the
transmission line. When moving along this line, it charges a
continuous portion of the transmission line, thus creating a
voltage difference of 1 volt between the transmission line and the
loop. Every 0.01 nanosecond advances, some charge (±Q) is obtained
from the battery, and the constant charge (±Q) flowing out of the
cell over a constant time interval (±t) is a constant current. The
negative current flowing into the loop is actually equal to the
positive current flowing out, and just in front of the signal wave,
the alternating current passes through the capacitance formed by
the upper and lower lines, ending the entire cycle.