[SI-LIST] Re: Driver slew rates

  • From: ravikumar potluri <potluri.ravikumar@xxxxxxxxx>
  • To: steve weir <weirsi@xxxxxxxxxx>
  • Date: Sat, 23 Nov 2013 18:19:24 +0100

As we have limited termination options internally (100 or 150ohms for
spartan3A-DSP) at the receiver I think I will go for external termination.
Additionally I have another question.  The reflection seen at the driver or
receiver are peculiar as the reflections are seen only an the lower half of
the signal as marked in the attachment
<https://www.dropbox.com/s/nof41blbhd8ilri/Simulation_Setup.png>.
I am asking this question to ensure that there is no problem with the IBIS
model I once again downloaded from TI and Spartan websites.

Thanks and Regards,


On Sat, Nov 23, 2013 at 6:00 PM, steve weir <weirsi@xxxxxxxxxx> wrote:

>  The channel length is electrically about 1.5X as long as the transition
> time.   That's easily 10X longer than where you can treat the line as
> lumped.
>
> The termination set-up of the receiver as it is performing in the
> simulation is not matched to the line. Check your model and set-up.
>
> Steve
>
>
> On 11/23/2013 8:47 AM, ravikumar potluri wrote:
>
> I am sorry but the time scale in nanoseconds with 8ns cycle time. Yes, I
> think I understand you correctly. The high transition rates indeed is the
> cause for these reflections?. I have already terminated the traces
> internally at the receiver. I think I need an external termination too If I
> am not mistaken.
>
>
> On Sat, Nov 23, 2013 at 5:41 PM, steve weir <weirsi@xxxxxxxxxx> wrote:
>
>>  The time scale is not visible in your traces, but the top trace is the
>> result of an unterminated transmission line that is electrically long
>> compared to the transition times.  The signal energy is not being absorbed
>> within the round trip so memories of transitions past haunt the present.
>> Change the configuration of the receiver input buffer to terminate the
>> signal.
>>
>> Steve.
>>
>> On 11/23/2013 8:26 AM, ravikumar potluri wrote:
>>
>>  Thank you all very much. Please find the attached figure. I downloaded
>> the IBIS model from TI and spartan websites. Also I used different drive
>> strengths but no improvement.
>>
>>  Regards,
>> Ravi
>>
>>
>> On Sat, Nov 23, 2013 at 5:20 PM, bala <balaseven@xxxxxxxxx> wrote:
>>
>>> Ravi,
>>> Pls check driver's input impedance and use low strength model if your
>>> tline
>>> is short.check your package model too.
>>> Regard
>>> bala
>>>  On 23 Nov 2013 21:34, "steve weir" <weirsi@xxxxxxxxxx> wrote:
>>> > No.
>>> >
>>> > Check your models and your simulation set-up.
>>> >
>>> > Steve.
>>> > On 11/23/2013 7:48 AM, ravikumar potluri wrote:
>>> > > Hello friends,
>>> > > If the slew rate of driver is much higher than the slew rate of
>>> receiver
>>> > > does this cause reflections on the transmission line?
>>> > >
>>> > >
>>> > > I am simulating ADS62P49, 250 MSPS ADC chip (Driver) with Spartan
>>> 3A-DSP
>>> > > (Reciever). I see lot of ringing at the output even when the chips
>>> are
>>> > > connected directly with termination in between and with no
>>> transmission
>>> > > line.
>>> > >
>>> > > Could someone explain this?
>>> > >
>>> > > Thanks and Regards,
>>> > > Ravi
>>> > >
>>> > >
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>>
>>
>> --
>> Steve Weir
>> IPBLOX, LLC
>> 1580 Grand Point Way
>> MS 34689
>> Reno, NV  89523-9998 www.ipblox.com
>>
>> (775) 299-4236 Business
>> (866) 675-4630 Toll-free
>> (707) 780-1951 Fax
>>
>> All contents Copyright (c)2013 IPBLOX, LLC.  All Rights Reserved.
>> This e-mail may contain confidential material.
>> If you are not the intended recipient, please destroy all records
>> and notify the sender.
>>
>>
>
>
> --
> Steve Weir
> IPBLOX, LLC
> 1580 Grand Point Way
> MS 34689
> Reno, NV  89523-9998 www.ipblox.com
>
> (775) 299-4236 Business
> (866) 675-4630 Toll-free
> (707) 780-1951 Fax
>
> All contents Copyright (c)2013 IPBLOX, LLC.  All Rights Reserved.
> This e-mail may contain confidential material.
> If you are not the intended recipient, please destroy all records
> and notify the sender.
>
>


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