[SI-LIST] Re: Less than 100 ohms differential impedance

  • From: Binayak Shrestha <binayaks@xxxxxxxxx>
  • To: jean-pierre.bouthemy@xxxxxxxxxxxxxxxxxx
  • Date: Tue, 25 Aug 2020 23:11:27 +0530

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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