Re: [SI-LIST] : Differential LVPECL termination

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From: Jim Freeman (freeman@broadcom.com)
Date: Thu Mar 30 2000 - 13:16:13 PST


Hi Ramesh,
    What is the signalling system used by the phy, The VTT suggests either SSTL_2 or HSTL.

Jim Freeman

ramesh srinivasan wrote:

> >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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