Re: [SI-LIST] : Transmission line termination

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From: Eric Goodill (ericg@redback.com)
Date: Fri Apr 06 2001 - 13:38:35 PDT


"Peters, Stephen" wrote:
>
> Hi Sunil:
>
> From a transmission line perspective you are correct -- there is no
> difference between the two. However, you do have to look at the output
> characteristics of the driver. If, for example, the driver was able to sink
> more current that it could source (typical TTL), then a termination to a Vtt
> would be preferred. (Obviously, if the driver is open-collector, then a
> termination (pullup) to Vtt is required). Power dissipation is another
> factor. If the signal is a control signal that spends most of it's time in
> the high state, then a termination to Vtt will dissipate less power than one
> to ground.

I'd like to add that there is no difference as long as VTT is sourced by
a good voltage source. Such a source has low output impedance and has a
good AC path to ground.

-Eric

>
> Regards,
> Stephen Peters
> Intel Corp.
>
>
> -----Original Message-----
> From: sunil-chandra.kasanyal@st.com
> [mailto:sunil-chandra.kasanyal@st.com]
> Sent: Friday, April 06, 2001 12:57 AM
> To: si-list@silab.eng.sun.com
> Subject: [SI-LIST] : Transmission line termination
>
> Hello all,
> What is the difference between these two terminations?Why?
> 1)
> -----------------------
> DRIVER->-----| TRANSMISSION LINE |-------------RECIEVER
> ----------------------- \
> Zo=50ohms /Rtt=50ohms
> \
> /
> ---GND
> 2)
>
> -----------------------
> DRIVER->-----| TRANSMISSION LINE |-------------RECIEVER
> ----------------------- \
> Zo=50ohms /Rtt=50ohms
> \
> /
> ------TERMINATION VOLTAGE=Vtt
>
> If signals of 5V come from drivers,no reflection will take place at the
> reciever ends.Since in above two cases,way of termination is
> different,what exactly the different uses of these two terminations.
>
> Regards
> Sunil
>
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-- 
_______________________________________________________
Eric Goodill                    Redback Networks
ericg@redback.com               300 Holger Way
voice: (408) 571-5319           San Jose, CA 95134-1362

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