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

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From: David Instone ([email protected])
Date: Fri Mar 09 2001 - 09:14:32 PST

Shripad,
   I missread your request as being how to verify on an actual device
that the spice prediction was correct. However, I would say that if you
want to check what voltage the spice predicts at the output of the
device then simulate using just the resistor. If you want to predict
what you would get at the end of a transmission line then use the
transmission line terminated by the resistors. Unless anyone else out
there knows better! 

-- 
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:
> 
> 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 --------------
> [email protected] (David Instone) wrote:
> To:SHRIPADARAJ AD <[email protected]>
> From:[email protected] (David Instone)
> Date:Fri, 09 Mar 2001 09:44:26 +0000
> CC:"[email protected]" <[email protected]>
> 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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