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What common transmission lines are typically found on a PCB?
There are usually two basic types of signal transmission line interconnects used in PCBs: microstrips and striplines. There is a third type – coplanar without a reference plane but it is not very common in use. A stripline is composed of a uniform trace – for the signal – located on the inner layer of a PCB.
How do you check transmission lines?
At any x, V/I = √(L/C). So far as the source of V(0, t) is concerned, the transmission line behaves in exactly the same way as a resistor of value √(L/C). We call this resistance the characteristic impedance of the transmission line.
Why are PCB tracks considered as transmission lines?
When a PCB operates at a high-frequency, its tracks’ behavior needs to be considered as transmission lines. Controlled impedance calculations are very important for these transmission lines so that signal reflections, crosstalk, noise, and ground bounce could be mitigated.
Which is a property of a transmission line?
For medium frequencies, only very long cables require special consideration. However, at 1 GHz many PCB traces must be treated as transmission lines, and as frequencies climb into the tens of gigahertz, transmission lines become ubiquitous. The most important property of a transmission line is the characteristic impedance (denoted by Z 0 ).
When is an interconnect considered a transmission line?
An interconnect is considered a transmission line when its length is at least one-fourth of the signal wavelength. Coaxial cables are commonly used as transmission lines, though PCB traces also serve this purpose.
When does the effect of a transmission line become significant?
If the interconnect length is greater than one-fourth of the signal wavelength, transmission-line effects become significant, and the influence of the interconnect itself must be taken into account. Recall that wavelength is equal to propagation velocity divided by frequency: