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bert_kak said:Guys any idea on how much line width will I use for a 75ohms composite video signal? Thanks
tennythomas said:The Simple PCB Impedance Calculator, PCB Stackup Impedance Calculator and
Trace Current Calculator are available in this link - **broken link removed**.
keith1200rs said:Analog/digital - it is all the same. What are the PCB parameters you are using (board thickness, dielectric etc)?
Keith.
bert_kak said:keith1200rs said:Analog/digital - it is all the same. What are the PCB parameters you are using (board thickness, dielectric etc)?
Keith.
here is my stack up.
middle core will be 1.24mm so it will be 1.6mm
on the right side is the computed line width for 50ohms single impedance line.
but when i try to compute for 75ohms it produces error because the line width would be too small.
keith1200rs said:That diagram is for a 50 ohm trace on 0.1mm thick PCB. For standard 1.6mm PCB I would expect the inner core to be thicker than 1.24mm.
Anyway, at 1.24mm you would need around 1mm wide track for 75 ohms and for 1.4mm around 1.15. How does that compare to your calculations?
By the way, bear in mind for video the bandwidth is relatively low. For short track lengths the impedance won't be critical. For example a 10mm track at 10MHz is only 0.2 degrees electrical length.
Keith.
karesz said:Hi Bert,
I used another older SW over long years from Polar, but their isnt usable on Internet PCs in the past ca. 8 years :-(...
It has had never bad values, seems to be very similar as your version...
For PRACTICABLE PCBs you MUST HAVE min. witdths of 100um & calculate pls for W1 ca 10% less as for W2...
I have had a flex board with only 26um trace widths(512 signals), but these is extrem_cost lot of maney & isnt really alldays business!
Then, are you sure that your PCB cores will have epsilonrel of 4.2!? Typical are 4.6..4.8.
For typical trace width values I remember by 0.5mm core thicknes as 0.25mm/100 Ohm for FR4 (E=4.7)...
BTW; if you are unsure in a SW`s resultat, calculate pls self per old knowed formulas for checking it!
K.
Hi Bert,bert_kak said:What are the factors for choosing PCB core? i search on the net and i think they usually use 4.2. How about dielectric besides core? should it be the same as the core? Thankskaresz said:Hi Bert,
...Then, are you sure that your PCB cores will have epsilonrel of 4.2!? Typical are 4.6..4.8.
For typical trace width values I remember by 0.5mm core thicknes as 0.25mm/100 Ohm for FR4 (E=4.7)...
BTW; if you are unsure in a SW`s resultat, calculate pls self per old knowed formulas for checking it!
K.
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