[SI-LIST] Re: Impedance confusion

lakshmi
It is common that people misunderstand how to set up Polar for offset 
stripline.  Look carefully about how the dimensions are done in Polar.  
IIRC there are three thicknesses that you need to specify.

T is the thickness of the trace

H1 is the dimension from the lowest plane to the bottom of the trace

H is the dimension from the lowest plane to the top plane.

You have two choices that will give you exactly the same value.

If you're using 1/2 oz copper the trace thickness is 0.6 mils
T = 0.6 mils
H1 = 5 mils
H = 5 + 22 mils + trace thickness = 27 mils + 0.6 mils = 27.6 mils

or

T = 0.6
H1 = 22 mils
H = 5 + 22 mils + 0.6 mils = 27.6  mils


Both entries will give the same solution.

best regards,

Scott

Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
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(401) 284-1827 Business
(401) 284-1840 Fax

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steve weir wrote:
> Study Yuriy's comments carefully. 
>
> Steve.
> Lakshmi N. Sundararajan - PTU wrote:
>   
>> Actually my confusion arose from using Polar for impedance calculation
>> for edge coupled offset stripline.
>> There is an input H1, which is the height of the trace from the plane,
>> now this can be either 5 mils or 22 mils depending...
>> The impedance varies based on which value I choose?!
>>
>> Is there a rule to pick only one of these two?
>>
>> Thanks,
>> -LN
>>  
>>
>>   
>>     
>>> -----Original Message-----
>>> From: Doug Brooks [mailto:dbrooks7@xxxxxxxxxx] 
>>> Sent: Friday, November 21, 2008 1:18 PM
>>> To: Lakshmi N. Sundararajan - PTU; si-list@xxxxxxxxxxxxx
>>> Subject: Re: [SI-LIST] Impedance confusion
>>>
>>> Your confusion may be because:
>>> Offset stripline implies a single-ended impedance, while 
>>> edge-coupled offset stripline implies a differential impedance.
>>> If the stackup is
>>> sig --- plane --- sig --- sig --- plane --- sig The inner 
>>> layers are asymetric stripline from a single-ended 
>>> standpoint, and if there is parallel coupling between the two 
>>> inner signal layers that coupling is broadside differential 
>>> coupling (unless, of course, it is simple crosstalk 
>>> coupling.) Hope that helps.
>>>
>>>
>>>
>>>
>>>
>>>
>>> At 12:18 PM 11/21/2008, you wrote:
>>>     
>>>       
>>>> Hi Team,
>>>>
>>>> Between these two stackup,
>>>> a) SIGTOP-PP(5 mils)-SIGINNER1-PP(22 mils)-SIGBOT
>>>> b) SIGTOP-PP(22 mils)-SIGINNER2-PP(5 mils)-SIGBOT
>>>>
>>>> While computing the impedance of the SIGINNER* layer, it is offset 
>>>> stripline or edge coupled offset stripline.
>>>>
>>>> Would the impedance be different between these two cases?
>>>> I ask this because, when board (a) is rotated it becomes 
>>>>       
>>>>         
>>> board (b) and 
>>>     
>>>       
>>>> hence I do not expect impedance to vary between these two stackups.
>>>>
>>>> Can anyone please confirm/clarify on this.
>>>>
>>>> Thanks,
>>>> -LN
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>
>
>   


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