[ibis-macro] Cornering IBIS
- From: "Walter Katz" <wkatz@xxxxxxxxxx>
- To: "IBIS-ATM" <ibis-macro@xxxxxxxxxxxxx>
- Date: Tue, 30 Aug 2011 17:34:26 -0400 (EDT)
All,
Corner is mentioned multiple times in IBIS 5.0.
e.g.
|
| Corner corner_name file_name circuit_name (module)
Corner Typ buffer_typ.v bufferb_io_typ
Corner Min buffer_min.v bufferb_io_min
Corner Max buffer_max.v bufferb_io_max
|
| The required "typ" column for all data represents typical operating
| conditions. For most [Model] keyword data, the "min" column describes
slow,
| weak performance, and the "max" column describes the fast, strong
| performance. It is permissible to use slow, weak components or models to
| derive the data for the "min" column, and to use fast, strong components
or
| models to derive the data in the "max" columns under the corresponding
| voltage and temperature derating conditions for these columns. It is
also
| permissible to use typical components or models derated by voltage
The implication for I-V and Ramp columns is
|
| e. Typ, Min, and Max must all be posted, and are derived at the same
| extremes as the I-V tables, which are:
|
| Ramp rates for CMOS models:
| typ = typical voltage, typical temp deg C, typical process
| min = minimum voltage, max temp deg C, typical process, minus "Y%"
| max = maximum voltage, min temp deg C, typical process, plus "Y%"
|
| Ramp rates for bipolar models:
| typ = typical voltage, typical temp deg C, typical process
| min = minimum voltage, min temp deg C, typical process, minus "Y%"
| max = maximum voltage, max temp deg C, typical process, plus "Y%"
So with minor exceptions min==slow and max==fast.
An EDA tool may support additional corners, but in any case they EDA tool
is responsible for mapping its "Corner" into IBIS typ, min and max values.
The bottom line is that all EDA tools have a concept of at least three
corners typ=nominal, min=slow=weak=worst_case, and
max=fast=strong=best_case.
Where min and max corners most often map into min and max columns in the
IBIS file.
The AMI format "Corner typ_value slow_value fast_value" suggest that the
EDA tool associates typ_value with typ=nominal, slow value with
min=slow=weak=worst_case and fast_value with max=fast=strong=best_case.
The EDA tool is not required to make this associating, but by using the
AMI format Corner, the model make is assuming that the EDA tool will make
that association.
The existence of format "Corner" had the implication that the EDA tool was
going to choose a Corner (typ, slow, fast).
The bottom line is that IBIS has a built in assumption that Corner shall
be "typ" "min" or "max". IBIS has confused a consistent way of associating
Corner with typ, min and max values. When AMI was developed 3 years ago,
we decided to eliminate this confusion by calling the three corners Typ,
Slow and Fast.
BIRD 124 (Dependency BIRD) makes the assumption that the EDA tool will
select one of the three corners for a simulation. The EDA tool must
already do this to choose the External Model, the IV and VT curves to
apply, as well as Model Parameters. Since the EDA tool is required to do
this to pick External Modles and IV/VT data, then the EDA tool knows which
Corner to use in AMI Corner parameters.
Walter
Walter Katz
wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 720.333-1107
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