[SI-LIST] : Differential LVPECL termination

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From: ramesh srinivasan (ramesh.srinivasan@wipro.com)
Date: Thu Mar 30 2000 - 01:59:21 PST


>From the datasheets of  LVPECL devices, I have found two different
kinds
of terminations:

1. Thevinin 50 ohms to VTT.
2. 100 ohms across the traces placed near to the receiver.

I am using a fiber optic transceiver which suggests a 100 ohm
termination for
the TX differential inputs, however the phy device which drives the
differential
input to the transceiver recommends a thevenin 50 ohm termination to
VTT.

I am not sure which termination to used and what are the advantages of
one over
the other.
Secondly the optical transceiver datasheets and the phy device recommend

different
terminations. Which terminations should I opt for ?

I assume that the terminations to opt for would be the ones mentioned in

the driver
data sheets rather than the ones recommended in the receiver datasheets.

Also I would like to know if the pull down resistor at the driver in
case of non-thevenin termination (mentioned above as 2.) Datasheets
again suggest
two different values (130 and 400 ohms)
 

**************************************************************
Ramesh Srinivasan
VLSI System Design Engineer-Global R&D Solutions
Wipro Technologies
3rd Floor,
No. 26, Sri Chamundi Complex, Bommanahalli,
Hosur Main Road,
Bangalore-560 068, India
Tel: 91-80-5722296-5408
E-mail: ramesh.srinivasan@wipro.com
www.wipro.com
The World's First SEI CMM Level 5 Software Services Company
**************************************************************
 
 

**************************************************************
Ramesh Srinivasan
VLSI System Design Engineer-Global R&D Solutions
Wipro Technologies
3rd Floor,
No. 26, Sri Chamundi Complex, Bommanahalli,
Hosur Main Road,
Bangalore-560 068, India
Tel: 91-80-5722296-5408
E-mail: ramesh.srinivasan@wipro.com
www.wipro.com
The World's First SEI CMM Level 5 Software Services Company
**************************************************************
 

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