[SI-LIST] Re: LVPECL AC COUPLING - CAPACITOR VALUE for 1.25G Ethernet
- From: "Sreejith Varma" <varma@xxxxxxxxxxxxxxx>
- To: <sa_jr@xxxxxxxxx>, <mikesa@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 6 Feb 2002 11:05:08 +0530
Hi Salvador,
Let us look at the requirement of AC coupling.
AC coupling is used to eliminate the DC component in a signal.
Basically used when we want to change the biasing of signals
[ie to connect between 5v and 3.3v devices].
You can consider the AC coupling capacitor as a simple high pass
filter [and this is exactly what we want, we want to remove the
dc and low frequency components, while passing all high frequency
harmonics].
So you need to find the Cut off frequency of the High pass filter
[filter formed with the ac coupling capacitor and the impedance
of track]. If the cut off frequency is low enough to remove all DC
components, it is sufficient.
In general we use a cap of 0.01 uf and it works out pretty well.
Too high or too low a value of capacitor attenuates / distorts the
signal.
Other comments are welcome :-)
Best regards
sreejith
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of salvador JR
Sent: Tuesday, February 05, 2002 7:49 AM
To: mikesa@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] LVPECL AC COUPLING - CAPACITOR VALUE for 1.25G
Ethernet
Hello All,
If I want to size the value of the AC coupling
capacitor used for DC blocking in a differential
LVPECL link should my input frequency range be the
same as the resonat frequency of the capacitor?
For example:
For a ceramic SMT capacitor of NPO dielectric
if the capacitance is 18 pF
The resonant frequency is 1250.44 MHz
The impedance (vs frequency) is 0.593 ohms
ESR = 0.59 ohms and
ESL = 0.9 nH
Where the impedance over frequency is calculated
using:
Z = sqrt[Rs^2 + (X_C -X_L)^2]
Where Rs = ESR
is 18pF the value of the capacitor for my DC blocking
in LVPECL differential link used for 1.25Gbps serial
data?
Thank you.
-- Sal
__________________________________________________
Do You Yahoo!?
Great stuff seeking new owners in Yahoo! Auctions!
http://auctions.yahoo.com
------------------------------------------------------------------
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:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//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:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//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:
