[SI-LIST] Re: Where could I find the Hspice model of varactor?
- From: "Steven M. Waldstein" <swldstn@xxxxxxxxxxxx>
- To: "Yiran Chen" <cyr_1976@xxxxxxxxx>
- Date: Fri, 12 Mar 2004 00:41:17 -0500
Viran,
I called it depletion because it behaves like a depletion mode device used
as an NMOS
load. By this I mean that the Vt is such that the device is always on so
there is a channel
even at Vgs=0. Vgs does not have to be greater that 0.5-0.7 to turn it on.
It is often used as a cap because it provides capacitance at any gate
voltage.
As far as decoupling it depends on what type of process you are in when you
talk about
device leakage. Are looking for core supply decoupling, or IO supply
decoupling?
For IO supplies at 0.25um and below we use the dual gate oxide devices ( 70
Angstrom gate).
The leakage for these devices are fine. You also want to look at the layour
and determine
what ESR you want.
For decoupling we have not used Nmos in an Nwell. We only use these inside
our PLLs.
For decoupling in the core we use both N and P devices inside the standard
cells.
Steve
-----Original Message-----
From: Yiran Chen [mailto:cyr_1976@xxxxxxxxx]
Sent: Friday, March 12, 2004 12:20 AM
To: si-list@xxxxxxxxxxxxx
Cc: swldstn@xxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Where could I find the Hspice model of
varactor?
Steven,
Yes, it is what I am thinking. However, I don't understand why you think
it is working at depletion state. When we apply VDD on the gate, a n-channel
will appears below oxide. I think it is accumulation. Am I wrong somewhere?
Or the misunderstanding of "depletion" and "accumulation". If you think it
is NMOS, that may be the reason why you are thinking it is depletion status.
Right? Sorry for such stupid questions.
Also, is it popular design for on-die decoupling capacitor? I know we
could use inversion NMOS and PMOS to implement the Decap but NMOS has large
leakage current and PMOS has slow speed? Are they the reasons to accept the
design that uses a NMOS in nwell?
Many thanks.
"Steven M. Waldstein" <swldstn@xxxxxxxxxxxx> wrote:
Yiren,
Are you really refering to on-die decoupling that uses a
NMOS in an NWELL? I know this is what TSMC refers to as a
varactor.
This is actually a depletion MOSFET. I know TSMC
has device models for these in there released HSPICE files.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of steve weir
Sent: Thursday, March 11, 2004 8:55 PM
To: cyr_1976@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Where could I find the Hspice model of varactor?
Do you really want to use a varactor as a decoupling capacitor??? The
capacitance of a varactor is typically in the 2-470pF region. That is
not
going to make much of a decoupling capacitor. I think On-semi has
models.
Steve
At 01:21 AM 3/12/2004 +0000, Yiran Chen wrote:
>I nee! d such kind of model to implement a decoupling capacitance in
>my design.
>
>Thanks.
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>or to administer your membership from a web page, go to:
>//www.freelists.org/webpage/si-list
>
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>List technical documents are available at:
> http://www.si-list.org
>
>List archives are viewable at:
> //www.freelists.org/archives/si-list
>or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
>Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
----------------------------------------------------------------------------
--
Do you Yahoo!?
Yahoo! Search - Find what youre looking for faster.
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
