Subject: Re: [IBIS-Users] FET Switch Model with internal pulldown resistor
From: Bob Ross (bob@teraspeed.com)
Date: Tue May 27 2003 - 09:30:02 PDT
Hello Moshiul:
Unfortunately, IBIS does not handle this case directly since the
[Submodel] keyword
modes are Driving and Non-Driving and do not apply to switch states.
Here are some suggested work-around solutions that may work in some
applications.
1. Use [Model Selector] to switch in a 500 ohm terminator. It must be
switched in
manually when the Series_switch is in the Off state. This might be the
most efficient
method if the switch control turns off several switches simultaneously.
However,
the user must control both the switch setting and model selector modes.
2. Issue two models, and do not allow the switch to have an Off state.
Document the
second model with a 500 ohm terminator at the drain side, and a high Z-model
terminator on the other side (and an [R Series] with 1 G ohm series element
to maintain connectivity). Load this model in place of the switch model
when
the high-Z state is used. Since all pinout configurations have to be
documented, this may not work well with swich ICs with many switches
and multiple On/Off combinations.
3. Some EDA tools may work if a Series_switch model has a high-Z state,
and a
terminator model is added to this manually or through EDA-specific commands
and interfaces.
All suggestions require the user (or a separate set of scripts) to
control the settings
manually.
Bob.
Haque, Moshiul wrote:
>I am trying to create an IBIS model for a parallel n-channel/p-channel
>mosfet switch. At the high impedance state (i.e. OFF state) drain side of
>the switch is connected to ground through a 500 ohm pulldown resistor. I am
>not sure how to model this pulldown resistor since this is connected only in
>the high-impedance state. If I model it in high impedance state the
>simulator will combine this characteristics with the ON state of the switch
>and the result will be inaccurate.
>
>Any idea how to create the model?
>
>Regards
>Moshiul Haque
>Standard Linear and Logic Marketing
>Texas Instruments Incorporated
>Ph: (903) 868-7153
>
>
>
-- 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 503-430-1065 bob@teraspeed.com 503-246-8048 Direct|------------------------------------------------------------------ |For help or to subscribe/unsubscribe, email majordomo@eda.org |with just the appropriate command message(s) in the body: | | help | subscribe ibis <optional e-mail address, if different> | subscribe ibis-users <optional e-mail address, if different> | unsubscribe ibis <optional e-mail address, if different> | unsubscribe ibis-users <optional e-mail address, if different> | |or email a written request to ibis-request@eda.org. | |IBIS reflector archives exist under: | | http://www.eda.org/pub/ibis/email_archive/ Recent | http://www.eda.org/pub/ibis/users_archive/ Recent | http://www.eda.org/pub/ibis/email/ E-mail since 1993
This archive was generated by hypermail 2b28 : Tue May 27 2003 - 09:36:42 PDT