PCB Construction
3.3 PCB Construction
Information in this section was obtained from the following source:
-Electromagnetic Compatibility Printed Circuit Board and Electronic Module Design, VEC workshop, Violette Engineering Corporation.
Characteristic impedance is the ratio of voltage to current in a transmission line wave traveling in one direction. This characteristic impedance is the value that is matched with our termination resistors so as to reduce reflections. This reduction in reflections improves signal to noise ratio on the line and reduces EMI caused by common mode voltages and spikes.
Two typical approaches are used for controlled impedance in
ZO | + | 60 |
| ln | 4h |
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| 0.67(0.8 W ) t) | (1) | ||||
0.475år ) 0.67 | ||||||||
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where εr is the permeability of the board material, h is the distance between the ground plane and the signal trace, W is the trace width, and t is the thickness of the trace. The differential impedance for a two microstrip traces can be approximated as follows with S being the distance between two microstrip traces:
Z | DIFF | + 2 Z | O | 1 * 0.48e*0.96sh |
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| (2) |
Stripline construction is also shown in Figure 3−6, the signal lines should be centered between the ground planes. The characteristic impedance of a stripline trace in a
ZO + | 60 | ln | 4h | (3) | ||
| 0.67p(0.8 W ) t) |
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år | ||||||
where εr is the permeability of the board material, h is the distance between the ground plane and the signal trace, W is the trace width, and t is the thickness of the trace. The differential impedance for a two stripline traces can be approximated as follows with S being the distance between two stripline traces:
Z | DIFF | + 2 Z | O | 1 * 0.374e*2.9sh |
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| (4) | ||
Note: | For | |||
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| are closely coupled (S < 12 mils, or 0,3 mm). | ||
Bill of Materials, Board Layout, and PCB Construction |