Author Topic: Differential Coplanar Waveguide Impedance ?  (Read 4427 times)

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Offline chris_leysonTopic starter

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Differential Coplanar Waveguide Impedance ?
« on: June 13, 2016, 10:19:13 am »
Hi

I'm using a short length of 0.5mm pitch flat flex as differential coplanar waveguide for routing 1000Base-T ethernet, and I'm using a single ground trace between the differential pairs, sketch attached. I haven't found any online calculators that cover this particular arrangement. The flat flex material is PET so the relative permittivity is around 3.0, does anybody have a calculator or field solver that will give me a ballpark estimate for differential impedance ?

Many thanks Chris.
 

Offline bktemp

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Re: Differential Coplanar Waveguide Impedance ?
« Reply #1 on: June 13, 2016, 10:30:37 am »
0.5mm FFC should have an impedance of around 100ohms for differential pairs. Here is an appnote about using FFC for USB:
http://ww1.microchip.com/downloads/en/AppNotes/00001579A.pdf
 
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Offline chris_leysonTopic starter

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Re: Differential Coplanar Waveguide Impedance ?
« Reply #2 on: June 13, 2016, 10:51:33 am »
Thanks bktemp  :-+ I guessed it wouldn't be to far from 100 Ohms.
 

Offline chris_leysonTopic starter

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Re: Differential Coplanar Waveguide Impedance ?
« Reply #3 on: June 13, 2016, 12:24:20 pm »
I just found this paper if anyone is interested, http://meritec.com/wp-content/uploads/2014/03/FFC-Impedance-Tests.pdf
 


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