[SI-LIST] Re: No need of termination within critical length??

Hi Sonu,

The reflections are still there. However, the critical length is defined 
from the rise/fall time of the driver, such that the round trip time for 
the reflection becomes short compared to the rise/fall time. This means 
the driver only changes its output voltage a fraction of the full swing 
during the time of a reflection round trip. The short round trip time 
means reflections die out faster than the signal rises/falls, and the 
small change in output voltage during the round trip time means the 
initial reflection is small (compared to the full signal swing). Thus 
for traces shorter than the critical length the reflections are small 
enough and die out fast enough to be ignored.

In theory, the reflections would make a small "ripple" on the 
rising/falling edge of a signal. This would not be good for a edge 
sensitive receiver, like a clock input, but I think with real 
transmitters/receivers the parasitics of the components will smooth this 
out to produce a monotonically rising/falling edge. Could someone else 
comment on this last point?

Regards,
Knut Georg Wiljugrein

Sonu Kurian N.D wrote:
> Hi All,
>
> I am puzzled about why  termination is not required if  trace length is 
> less than critical length.
> I read like if a driver encounters a reflected signal when it is 
> rising(driving) , its able to absorb reflection.Is it so?
> Or is the situation like ..the reflections will be there..but the Setup 
> condition can be met..so we need not worry..??
> Can anyone please throw some light on this..
>
> Many thanks,
> Sonu
>
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> http://www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
>                 http://www.si-list.net
>
> List archives are viewable at:     
>               http://www.freelists.org/archives/si-list
> or at our remote archives:
>               http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
>               http://www.qsl.net/wb6tpu
>   
>
>
>
>   

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field


List technical documents are available at:
                http://www.si-list.net

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu
  

Other related posts: