( ESNUG 399 Item 8 ) --------------------------------------------- [08/08/02]
Subject: ( ESNUG 398 #10 ) 2.5-D RC Estimation & Correlation In PhysOpt
> I finally got the answer to my question from a Synopsys AE. The PhysOpt
> 2.5-D extraction engine does not need RC correlation. Actually, there is
> no way to even obtain correlation numbers in the current rev of PhysOpt.
>
> The numbers which were printed out by estimate_rc (and were confusing me)
> are there for backward compatibility and are comparing the actual DSPF to
> the numbers in the library. Basically, these numbers should be ignored.
>
> - Mahsa Vahidi
> Mindspeed Technologies San Diego CA
From: Vandana Kaul <vkaul@synopsys.com>
Hi John,
The 2.5 D extraction parameter based RC estimation in PhysOpt should
eliminate the need for RC correlation. If this extraction parameter based
estimation is working properly, your PhysOpt log file will contain a message
like the following:
Information: Extractor based RC computation is enabled. (PSYN-140)
As Mahsa Vahidi indicates in ESNUG 398 #10, when you run the "estimate_rc"
command for RC correlation, the log file continues to show values based
upon the 1D values, even if you are using the extraction based approach.
These messages look as follows:
Capacitance - horizontal 0.0002105 vertical : 0.00017
Resistance - horizontal 0.000618 vertical : 0.0002368
These numbers are calculated by comparing the post-route backannotated data
with the 1D values calculated from the physical library. This can be
confusing. For an annotated (delay/load) design, no matter which RC model
is used, the "estimate_rc" command will always report 1D based values. The
"compare_rc" command, however, will generate a plot showing the correlation
between the extraction based values and the post-route backannotated values.
This curve should show very good correlation between the post-PhysOpt and
post-route values. The goal is to eliminate the need for RC correlation
altogether.
John, some of your readers may not be familiar with the newer 2.5D flow,
so I would also like to provide the following background information on
parasitic estimation in PhysOpt, so everyone is on the same page.
The early (pre-2001.08) PhysOpt releases used RC parameters that were
directly converted from LEF parameters. The LEF syntax, however, puts a
limit on accuracy as capacitive modeling was restricted to a basic 1D
model with an area cap and an edge cap.
In the 2001.08 release of PhysOpt, the .plib started to support a more
detailed (2.5D) cap model that includes: area caps, side wall caps,
inter-layer fringe caps and intra-layer fringe caps. These new cap models
require the use of a Routing Wire Model, RWM, to give PhysOpt an idea of
what you expect for routing densities per layer, coupling between layers
and on the same layer.
Beginning in the 2002.05 release, PhysOpt supports RC models based on just
extraction parameters: field oxide thickness, field oxide permittivity,
layer thickness, layer lateral oxide thickness, layer lateral oxide
permittivity, layer oxide thickness and layer oxide permittivity.
In summary, there are three types of RC models you can use with PhysOpt:
1) LEF based plib RC models
* Limited to 1D models.
2) Area Cap, SideWall Caps, Interlayer Fringe caps, Intra-layer caps
* Requires a RWM for layer densities
* Support started in 2001.08
3) Extraction based models
* Uses process extraction parameters
* Support started in 2002.05
The following two points might further clarify how the extraction plib
models work in a PhysOpt flow:
1) The plib defines the metal width, spacing, pitch, oxide thickness,
and permittivity. Therefore, PhysOpt can calculate under-the-hood
values for area cap, side wall cap, intra-layer fringe caps, intra-
layer caps, etc. based on assumed adjacent wires.
2) Next, PhysOpt is already building routing data per gcell when it
calculates congestion maps, so this concept can be extended
under-the-hood to calculate a RWM based on your design and the
routing densities.
Therefore, I see the new extraction based plibs as an extension of the
area cap, fringe cap based plib noted above. The advantage of this flow is
a user does not have to supply a RWM. PhysOpt will calculate the RWM
based on your design.
NOTE: We found one bug with the 2.5D extraction based method in 2002.05.
This bug has to do with accuracy when performing RC calculation around
large hard macros/RAMs. This will be fixed in version 2002.05-SP1, which
should be released in the September time frame. For designs that contain a
lot of channels between hard macros/RAMs, it is best to wait for this
release to begin using the extraction based method.
- Vandana Kaul
Synopsys, Inc. Mountain View, CA
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