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PECL Logic Design Differential Logic.

 
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joeRoche



Joined: 14 Jul 2008
Posts: 1
Post14 Jul 2008 15:42   PECL Logic Design Differential Logic.
Hello,

I have a question about PECL logic Design.
I am new to this technology so I have a quick question.

PECL logic design uses (emitter coupled Logic). This is Differential Logic and the tracks on the PCB are transmission lines and have to be terminated.

Does anybody know of a reference book or designer manual with a reference design that I can look at.

I am using on-semi differential logic for a high speed application and I am concerned about fanout.

Can the PECL device drive more than one input like an RS-485 network . Or do you have to use buffers.


Any info would be helpful.
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banjo



Joined: 24 Dec 2005
Posts: 476
Helped: 89
Post12 Aug 2008 18:34   PECL Logic Design Differential Logic.
On Semiconductor is the leader for ECL and PECL components. They took over the product line formerly run by Motorola. Go to http://www.onsemi.com
and search for PECL. You will find numerous design guides.

You can fanout PECL. However, the routing must be daisy-chained with the termination resistors at the far end. Most common mistakes are to either place the termination resistors at the source rather than the load. The other mistake is to route a star pattern rather than daisy-chain. Personally, I usually only fanout to 2 or 3 devices. Beyond 3, I use buffer chips to generate multiple copies of the signal. PECL or ECL is only really useful for high speed stuff. Remember this is matched length differential routing.
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