Re: [SI-LIST] : driving into 50 Ohm impedence

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From: Nianci Wang (nwang@amcc.com)
Date: Fri Mar 09 2001 - 09:19:56 PST


Shripad,

You may want to use 50 ohm resistor for start point in your simulation.
but eventually you may need to include the transmission line model,
termination, your Rx spice netlist and the package parasitic for both Tx
and Rx chip.

Regards

Nianci

SHRIPADARAJ AD wrote:
>
> Thanks David,
>
> You are right 1.0625, but drive requirement is 50/75 Ohm.
>
> While simulating do I need to put just a 50 Ohm resistor at Out pin of Transceiver or should I bring a transmission line into picture inbetween.
>
> Thanks
>
> Shripad
>
> ------------- Original Message --------------
> david_instone@uk.xyratex.com (David Instone) wrote:
> To:SHRIPADARAJ AD <adsraj@rediffmail.com>
> From:david_instone@uk.xyratex.com (David Instone)
> Date:Fri, 09 Mar 2001 09:44:26 +0000
> CC:"si-list@silab.eng.sun.com" <si-list@silab.eng.sun.com>
> Subject:Re: [SI-LIST] : driving into 50 Ohm impedence
>
> Shripadaraj,
> Sound like a PECL device to me. Terminate each side of the
> differential output to Vdd-2.0V using a 50 ohm resitive load. Each
> side of the output should then have a total swing of 900mV measured
> across that load, giving 1800mV p-p measured between the two outputs.
> The 50 ohms to Vdd -2 can be done using 50 ohms to a voltage supply at
> Vdd-2 which can sink current to ground or by use of a thevenin euivalent
> resistance of 50 ohms from a potential divider across the supply rails,
> or a combination of the two.
>
> However, you say it is a Fibre Channel device, possibly, but be aware
> that FC operates at 1.0625 Gbps (or 2.125) and is specified as a 75/150
> ohm system, the 50 ohm resistors would be 75 ohms. Gigabit Ethernet
> operates at 1.25 Gbps and is also a 75/150 system. However, some IC
> manufacturers also specify their drivers at 50 ohms, as some system
> builders prefer to operated FC at 50/100 ohms inside their equipment.
>
> Hope this helps
> --
> Regards
>
> Dave Instone. Compliance Engineer
> Storage Systems Development, MP24/22
> Xyratex, Langstone Rd., Havant, Hampshire, P09 1SA, UK.
> Tel: +44 (0)23-92-496862 (direct line)
> Fax: +44 (0)23-92-496014
> http://www.xyratex.com Tel: +44 (0)23-92-496000
>
> SHRIPADARAJ AD wrote:
> >
> > Hi all SI expert,
> >
> > This may be a silly question, but not for me.
> >
> > I have a fibre channel transceiver operating at 1.2 Gbps data rate. It has differential o/p and o/p level specs are as below,
> >
> > 1800 mV(p-p) driving 50 Ohm to VDD-2.0v.
> >
> > What does it mean ? I am novice to this field.
> >
> > I have beeen given spice netlist of the o/p driver and asked to verify that driver meet about voltage level requirement. How should do that ?
> >
> > Any pointers in this regard would be of great help to me
> >
> > Thanks in advance
> >
> > Shripad
> >
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