And - adding to Binayak's comment - pay attention to termination values and
your connector impedances, which will be 100 ohms more often than not. The
lower speeds can typically handle a short impedance discontinuity from the
board to a connector, but you'd want to simulate the high-speed signals, making
sure to model the discontinuities and terminations.
Bill Hargin
Director of Everything
Z-zero ▪ Innovative PCB Stackup Design ▪ www.z-zero.com
billh@xxxxxxxxxx ▪ 425-301-4425 ▪ Skype: bill.hargin
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On Behalf Of
Binayak Shrestha
Sent: Tuesday, August 25, 2020 10:41 AM
To: jean-pierre.bouthemy@xxxxxxxxxxxxxxxxxx
Cc: Si-list <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Less than 100 ohms differential impedance
Just add to my previous comment....some high speed interface demand a
particular impedance. Make sure you go through the spec properly on to see if
you can change them or not.
On Tue, 25 Aug, 2020, 11:08 pm Binayak Shrestha, <binayaks@xxxxxxxxx> wrote:
Jean,
IF you are able to maintain a constant uniform impedance environment
from the driver pads to the receiver pads, it should be fine....BUT
pay attention to the "IF condition" very carefully.
- binayak
On Tue, 25 Aug, 2020, 3:33 pm BOUTHEMY Jean-Pierre, <
jean-pierre.bouthemy@xxxxxxxxxxxxxxxxxx> wrote:
Hello SI experts,
I have many differential pairs in my design that should be matched to
Zdiff = 100 ohms on the PCB.
But my stackup has very thin dielectric material and I won't be able
to reach more than 80 ohms differential impedance.
This is typical value, thus I can expect Zdiff to be as low as 70 ohms.
I would like to know the electrical and functional impact of
Zdiffp-80 ohms on following differential signals:
o LVDS 100Mbps
o Ethernet 100Base-TX
o Ethernet 1000Base-BX (Xilinx Multi-Gigabit Transceiver)
o Ethernet SGMII (Xilinx Multi-Gigabit Transceiver)
o 25MHz LVDS Clock
o 200MHz LVDS clock
o 125MHz AC-coupled LVPECL clock
Thank you for your answers.
Regards.
[cid:image019.png@01D38BAE.3AF37340]
Jean-Pierre BOUTHEMY
Ingénieur Etude et Développement en Electronique Département R&D
Centre de Compétences Groupe Microélectronique Systèmes de Mission
de Défense
Tel.: +33 (0)2 23 55 42 28
jean-pierre.bouthemy@xxxxxxxxxxxxxxxxxx<mailto:
jean-pierre.bouthemy@xxxxxxxxxxxxxxxxxx>
THALES
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