Subject: [IBIS-Users] ECL Termination Voltage Question
From: Fisher, Thomas (tomfisher@ti.com)
Date: Thu Jan 15 2004 - 08:16:08 PST
Bob, thanks for the response. Do I understand you correctly in that the Vtt
is pre-set (base on Vcc) within the model type, 'output_ECL?' If this is
the case, then it creates a problem for this particular model.
Secondly, I am using the [Rising Waveform] and [Falling Waveform] but it
does not correct this problem. The VT tables are created from Spice with
200 ohm resistors to ground. If 'output_ECL' is wanting to use the pre-set
Vtt = Vcc - 2V with 50 ohm resistors, this is a problem.
Who could I contact that could explain how the 'output_ECL' model type is
constructed? Thanks. -T-
Regards,
Thomas Fisher
Senior Systems Engineer
Texas Instruments, Inc. Business: 214 480-3736
P.O. Box 660199 MS8710 Fax: 214 480-3160
Dallas, TX 75266-0199 <mailto:tomfisher@ti.com> tomfisher@ti.com
Tom:
My responses are in your text.
Bob
Fisher, Thomas wrote:
> All,
>
> I have a PECL driver that I am modeling that has a non-standard load (pi
> network to ground) which results in a larger Vod. (1.2-V vs. 800mV)
> What happens during simulation is the single-ended waveform depicts a
> slowness of the rising edge which results in a plateau effect on the
> rise/fall of the differential waveform. (It looks great when simulating
> in TISpice) Most (P)ECL termination is going to be 50 ohms to Vtt for
> both non-inverting and inverting outputs whereas Vtt = Vcc - 2-V. Under
> the load I am simulating we are using 200 ohms to ground. (customers'
> request)
>
>
>
> Having said that, looking in the 3.2 spec on page 78 under ramp rates
> model_type for output_ECL it mentions 50 ohm resistor to the termination
> voltage (Vterm = Vcc - 2-V). Is this Vterm embedded into the
> specification?
Yes
Is there a way to specify that the load is 200 ohms to
> ground?
Yes, but you must use the [Rising Waveform] and [Falling Waveform]
method and describe the waveform. This will override the [Ramp]
keyword, which cannot correctly specify the situation you describe.
I believe this might be causing the abnormality. Any
> help/insight would be appreciated. Thanks in advance.
>
>
>
> Regards,
>
> Tom Fisher
>
>
>
-- Bob Ross Teraspeed Consulting Group LLC Teraspeed Consulting Group LLC 2926 SE Yamhill St. Device Modeling Division Portland, OR 97214 13610 SW Harness Lane 503-239-5536 Beaverton, OR 97008 http://www.teraspeed.com <http://www.teraspeed.com> 503-430-1065 bob@teraspeed.com <mailto:bob@teraspeed.com?subject=Re:%20%5bIBIS%5d%20ECL%20Termination%20Vol tage%20Question&replyto=40042324.90405@teraspeed.com> 503-246-8048 Direct-----------------------------------------------------------------
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