HI,i wanna know what is the impedance board?

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I would guess the OP is asking about the difference between a board with controlled-impedance and a board without controlled-impedance.
 
Nigel Goodwin said:
That makes no sense to me either?.
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Boards with high-speed signals require controlled-impedance routing to ensure that signal reflections do not interfere with the transmitted signals. This requires controlled layer stackups, trace width, trace spacing, etc. Low-speed boards do not require this sort of attention, and routing requirements are much looser as reflections will not have a significant impact on the signal integrity. Thus, we have a board with controlled-impedance and a board without controlled-impedance.
 
DerStrom8 said:
This requires controlled layer stackups, trace width, trace spacing, etc.
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But would just looking at a board be enough to identify a board with controlled impedance? That seems to be the aim of the TS.
 

That's sounds rather like a massive extrapolation from the OP's question
 
alec_t said:
But would just looking at a board be enough to identify a board with controlled impedance? That seems to be the aim of the TS.
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Generally, no - you cannot tell if a board uses controlled-impedance routing just by looking at it. You can get potential hints (i.e. differential pairs), but that is not enough in itself to identify controlled-impedance.

Nigel Goodwin said:
That's sounds rather like a massive extrapolation from the OP's question
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Agreed. However, by reading the original post it is easy to tell that the TS is new to PCB design and may not know enough yet about the subject to form a proper question. Therefore, I took my best guess based on the question that was posed. I am hoping the OP will clarify, and if my guess happens to be correct then it will help provide some of the terminology he needs to ask the right questions.
 
alec_t said:
But would just looking at a board be enough to identify a board with controlled impedance? That seems to be the aim of the TS.
Click to expand...
Not 100% of the time, but generally speaking, yes.

I agree with Der about the intent of the question. And yes, I think an experienced designer can recognize impedance control techniques (on the surface layers only, of course) with only visual inspection. But part of that inspection includes the physical layout and the components, especially the ICs and connectors. For example, SMA and SMB connectors are a pretty sure indicator of very high freq signals that require impedance controls.

ak
 
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