BIRD19.1

IBIS Members:

BIRD19.1 is a revision of BIRD19 to deal only with V_fixture_min and
V_fixture_max subparameters.

Bob Ross,
Interconnectix, Inc.

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                 Buffer Issue Resolution Document (BIRD)

BIRD ID#: 19.1
ISSUE TITLE: V_fixture Subparameter Min/Max Additions
REQUESTOR: Bob Ross, Interconnectix, Inc.
DATE SUBMITTED: 8 August 1994
DATE REVISED: 13 August 1994
DATE ACCEPTED BY IBIS OPEN FORUM: Pending

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STATEMENT OF THE ISSUE:

There are cases with respect to certain devices including CMOS logic where the
[Rising Waveform] and [Falling Waveform] fixture load specifications are not
adequate to define the min and max table loads. Additional sub- parameters
for [Rising Waveform] and [Falling Waveform] are proposed: V_fixture_min and
V_fixture_max.

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STATEMENT OF THE RESOLVED SPECIFICATIONS:

The [Rising Waveform], [Falling Waveform] keyword description is presented
along with changes in the text related to including the sub-parameters
"V_fixture_min" and "V_fixture_max". Changed lines are designated by "|*".

|==============================================================================
| Keywords: [Rising Waveform], [Falling Waveform]
| Required: No
| Description: Describes the shape of the rising and falling edge
| waveforms of a driver.
|* Sub-Params: R_fixture, V_fixture, V_fixture_min, V_fixture_max,
|* C_fixture, L_fixture,
| R_dut, L_dut, C_dut
| Usage Rules: Each [Rising Waveform] and [Falling Waveform] keyword
| introduces a table of time vs. voltage points that
| describe the shape of an output waveform. These
| time/voltage points are taken under the conditions
| specified in the R/L/C/V_fixture and R/L/C_dut
| sub-parameters. The table itself consists of
| one column of time points, then three columns of
| voltage points in the standard typ, min, and max format.
| The four entries must be placed on a single line and
| must be separated by at least one white space or tab
| character. All four columns are required. However, data
| is only required in the typical column. If minimum
| or maximum data is not available, use the reserved word
| "NA". The first value in the time column need not be '0'.
| Time values must increase as one parses down the table.
| The waveform table can contain a maximum of 100 data
| points. A maximum of 100 waveform tables are allowed per
| model. Note that for backwards compatibility, the existing
| [Ramp] keyword is still required.
|
| A waveform table must include the entire waveform;
| i.e., the first entry (or entries) in a voltage column
| must be the DC voltage of the output before switching
| and the last entry (or entries) of the column must be
| the final DC value of the output after switching.
|
| A [Model] specification can contain more than one rising
| edge or falling edge waveform table. However, each new
| table must begin with the appropriate keyword and sub-
| parameter list as shown below. If more than one rising or
| falling edge waveform table is present, then the data in
| each of the respective tables must be time correlated.
| In other words, the rising (falling) edge data in each
| of the rising (falling) edge waveform tables must be
| entered with respect to a common reference point on the
| input stimulus waveform.
|
| The 'fixture' sub-parameters specifies the loading
| conditions under which the waveform is taken. The R_dut,
| C_dut, and L_dut Sub-params are analogous to the
| package parameters R_pkg, C_pkg and L_pkg and are used
| if the waveform includes the effects of pin
| inductance/capacitance. The diagram below shows the
| interconnection of these elements.
|
| PACKAGE | TEST FIXTURE
| _________ |
| | DUT | L_dut R_dut | L_fixture R_fixture
| | die |---@@@@@--/\/\/\--o-----|--@@@@---o---/\/\/\----- V_fixture
| |_________| | | |
| | | |
| | | |
| C_dut === | === C_fixture
| | | |
| | | |
| GND | GND
|
| Only the R_fixture and V_fixture sub-parameters are
| required, the rest of the sub-parameters are optional.
| If a sub-parameter is not used, its value defaults to
| zero. The sub-parameters must appear in the text after
| the keyword and before the first row of the waveform
| table.
|
|* V_fixture defines the voltage for typ, min and max
|* supply conditions. However, when the fixture voltage
|* is related to the power supply voltages, then the
|* sub-parameters V_fixture_min and V_fixture_max can
|* be used to further specify the fixture voltage for
|* min and max supply voltages.
|*
|------------------------------------------------------------------------------
[Rising Waveform]
R_fixture = 500
V_fixture = 5.0
|* V_fixture_min = 4.5 |Note, R_fixture is connected to Vcc
|* V_fixture_max = 5.5 |Specified, but not used in this example
C_fixture = 50p
L_fixture = 2n
C_dut = 7p
R_dut = 1m
L_dut = 1n
|Time V(typ) V(min) V(max)
 0.0ns 0.3 0.5 NA
 0.5ns 0.3 0.5 NA
 1.0ns 0.6 0.7 NA
 1.5ns 0.9 0.9 NA
 2.0ns 1.5 1.3 NA
 2.5ns 2.1 1.7 NA
 3.0ns 3.0 2.7 NA
 3.5ns 3.2 3.0 NA
|
[Falling Waveform]
R_fixture = 50
V_fixture = 0
|Time V(typ) V(min) V(max)
 10.0ns 3.2 3.0 NA
 10.5ns 3.0 2.7 NA
 11.0ns 2.1 1.7 NA
 11.5ns 1.5 1.3 NA
 12.0ns 0.9 0.9 NA
 12.5ns 0.6 0.7 NA
 13.0ns 0.3 0.5 NA
 13.5ns 0.3 0.5 NA
|
|=============================================================================

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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION

John Brennan writes 7/29/94,
"I have a question on the V_fixture ibis sub-keyword for
[Falling Waveform]. This variable appears to expect
1 value, ie, typically the nominal power supply value.
Since I use the same deck to measure [Ramp] as [Falling
Waveform], my deck has the load resistor hooked to the power
supply, which will be different for typ, min and max."

"Does this present a problem to the simulation vendor that
V_fixture cannot handle a min and max value, or If I enter
three values will they be handled correctly. Should I change
my deck so the the load resistor is hooked to the nominal supply
value and not vary it for min and max?"

"How important is V_fixture? Also, are the values in the example
in spec ver2.0 backwards? Wouldn't a [Falling Waveform] be
pulling against a logic "1" voltage, and a [Rising waveform]
be pulling against a GND type voltage?"

Bob Ross responds 7/29/94,
"My initial response is that you uncovered a valid condition which we did not
consider fully. We should have allowed a V_fixture_min, and V_fixture_max
for cases where the fixture is tied to Vcc or for cases where it represents
the Thevenin voltage (and can change). The same will apply for the [Model]
subparameter Vref. It may need a Vref_min and Vref_max also. This should
be the subject for further consideration and probably a BIRD."

An alternative approach would be to redefine V_fixture and Vref similar to the
C_comp subparameter on one line in the typ_min_max format. This was not
chosen because it could create an unnecessary enlargement of IBIS Version 2.1
to be compatible with IBIS Version 2.0 and also because the additional
sub-parameters introduced here may be used less frequently.

For completeness, V_fixture_typ and Vref_typ could also have been introduced.
However, with the current definition, these are redundant.

The proposed additions in BIRD19 of Vref_min and V_ref_max subparameters
of [Model] have been deleted in BIRD19.1 because they are typically not
used in timing specifications.

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ANY OTHER BACKGROUND INFORMATION

As additional information, a similar problem was encountered in specifying
the input waveform amplitudes for the s2ibis program under min and max
supply conditions. This is particularly applicable for CMOS logic where
a typical voltage range is from 0V to 5V. However, if the supply voltage is
at min (say 4.5V), one would expect the Input voltage range to be from 0V
to 4.5V). The default condition for s2ibis for IBIS Version 1.1 is to
adjust the Input Voltage directly proportional to Vcc. So for a typical
TTL Input specification, the Input voltage specified from 0V to 3V is
actually 0V to 3V for typ, 0V to 2.5V for min, and 0V to 3.5V for max for
a +/- .5V Vcc change. This default condition (which defines the SPICE
PULSE command) can be overridden (along with the default Input ramp rise
and fall times of .1ns) under each condition by optional specifications:

**Input_Ramp_min <vil> <vih <tr> <tf>
**Input_ramp_typ <vil> <vih> <tr> <tf>
**Input_ramp_max <vil> <vih> <tr> <tf>

So with these specifications, the Input ramp specification can be set to
a fixed voltage range such as 0V to 3V for typ-min-max extractions.
Received on Sat Aug 13 18:48:30 1994