The impedance of the impedance: the wiring is determined by the copper and the weight of the cross sectional area. L oz copper has, for
example, o. 49 m Ω/per unit area of impedance. Capacitance: wiring capacitance is an insulator (EoEr), current to the range of (A) (h) and line
spacing. Expressed in equation for C = EoErA/h, Eo is the free space of the dielectric constant (8.854 pF/m), Er is PCB substrate relative
dielectric constant (4.7) in FR4 rolling.
Inductance, inductance average distribution of the wiring in wiring, approximately 1 nH/m.
For 1 oz copper wire in o. 25 mm (10 mil) thick FR4 rolling cases, located on the ground layer at the top of the 0.5 mm wide (20 mil), 20 mm (800
mil) long the impedance of the line can produce 9.8 m Sunday afternoon, 20 nH inductance and 1.66 pF between coupling capacitance. The
above value compared with the components of the parasitic effect, which can be ignored, but the sum of all the wiring may be beyond the
parasitic effects. Therefore, in this must be taken into account by its designer. PCB wiring general guidelines:
(1) increase go line spacing in order to reduce the crosstalk capacitance coupling;
(2) the parallel of cloth to make the power cord and ground PCB capacitor to achieve the best;
(3) will be sensitive to high frequency line cloth away from the high noise power cord; In order to reduce the power cord
(4) widen the power cord and ground and ground impedance.
2.2 segmentation
Segmentation refers to the physical segmentation is used to reduce the coupling between different types of wire, especially through the power
line and ground.
With the segmentation technology to four different types of circuit examples of separated. On the ground surface, non-metallic groove used to
separate the four ground surface. L and C as a part of the board of each filter. Reduce the coupling between the power of the different circuit.
High speed digital circuits because of its instantaneous power demand and higher requirements on power supply at the entrance. Interface
circuit may need to electrostatic discharge (ESD) and transient suppression device or circuit. For L and C, it is best to use different values of L
and C, rather than using a large, L and C, because it can provide different filtering characteristics for different circuit.
2.3 partial decoupling between the power and IC
Partial decoupling can reduce the noise propagation along the power line. Connect the power supply input port large capacity bypass capacitors
between the PCB it plays the role of a low frequency pulse filter, at the same time as a potential reservoir in order to satisfy the demands of
emergency power. In addition, at each IC should have a decoupling capacitor between power supply and ground. The decoupling capacitor
should be as close to the pins. This will help to filter out noise switch IC.
