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Design >> Mixed-Signal Design >> PCBs with 50 Ohm Zo
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Message started by vivkr on Jul 6^th, 2006, 9:22am

Title: PCBs with 50 Ohm Zo
Post by vivkr on Jul 6^th, 2006, 9:22am

Various signal sources etc. are designed for 50 Ohm termination. However, if the PCB traces have a different level of characteristic impedance (Zo), then there will be some reflection, as the signal passes through the short PCB trace to a 50 Ohm termination resistance on-board, or am I mistaken?

Is it possible to get PCBs where Zo is 50 Ohm? How would one do that?

Regards
Vivek

Title: Re: PCBs with 50 Ohm Zo
Post by ACWWong on Jul 7^th, 2006, 1:56am

Yes you are correct, us RFIC designers are constantly getting PCBs made with differring characteristic impedance (often 50ohm, but not always necessary) tracks to match the impedance we are teminating in (and therefore not introduce rotation on a smith chart). We do this by altering the track width depending on the other parameters of the PCB (er, dielectric thickness, conductor dimension etc.)

There are quite a few tools out there for designing microstrips (single track on top layer of PCB) or stripline (embedded track).

As I don't design PCBs (i only check that the PCBs made meet my criteria) i often use the lmg program included in cadence.

But i'm sure if you do a google for you'll find some good stuff or try
http://www.circuitsage.com/tline.html

hope this helps