[SI-LIST] Re: 90 OHM Differential Impedance

When you think of differential pairs you are well served to think of 
each pair as a two signal bus with particular coding and timing 
requirements.

Run loosely coupled lines and you will be able to stay close to 45 S/E 
while hitting 90 differential.  Unless you are running up aginst tight 
space constraints you should find loosely coupled is easier to route.  
If you mismatch S/E impedance severely then you will get substantial 
standing waves that can create a number of different problems.

Steve.

Saril wrote:
> Hi All,
> Â 
> Basically USB signals require 45 Ω  characteristic impedance and have a 
> target differential impedance of 90 Ω. 
> The 90 Ω Differential impedance can be achieved without having the single 
> ended characteristics impedance of 45 Ω. Sometimes the Single ended 
> characteristics impedance may be 50 Ω but still we can have the 
> differential impedance of 90 Ω, if we tune the differential trace 
> separation. 
>
> How important is it to meet single ended as well as differential impedance 
> requirements together, can I just neglect the single ended impedance and 
> consider only the differential impedance value. 
>
> Thanks in advance.
>
>
> Regards,
> Saril Kaiprath
>
>
>
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