Subject: [IBIS] BIRD75 -- Additional Information Related to C_comp Refinements
From: Peters, Stephen (stephen.peters@intel.com)
Date: Fri Jun 28 2002 - 13:39:36 PDT
Greetings:
During the editorial review of IBIS 4.0 several issues were noted with
text added by BIRD65, C_comp
Refinements. The following BIRD is intended to address these issues. While
no technical changes were
made, and the intent of BIRD65 remains the same, the text changes were
extensive enough to warrant
official documentation as a BIRD.
BIRD76 is scheduled for discussion and vote at the June 19, 2002
teleconference, and will proceed any
vote on the IBIS 4.0 specification itself.
If you have any comments on this bird please you are encouraged to post them
to the IBIS reflector
for discussion.
Regards,
Stephen Peters
Intel Corp.
Chair EIA/IBIS Open Forum
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BIRD ID#: 76
ISSUE TITLE: Additional Information Related to C_comp Refinements
REQUESTER: Arpad Muranyi, Stephen Peters, Intel
DATE SUBMITTED: June 28, 2002
DATE ACCEPTED BY IBIS OPEN FORUM: Pending
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STATEMENT OF THE ISSUE:
During the review of IBIS 4.0, several documentation issues were raised with
the original BIRD 65.2. Important information was only documented in the
"Statement of the issue", "Statement of the resolved specifications" and
"Analysis data/path that led to specification" sections of the BIRD.
Specifically, there was no text added to the specification that described
how
the additional distributed capacitances created by BIRD65 were to be applied
to the prototype simulation model. In addition, some of the usage rules did
not
distinquish between use of a subparameter and use of its value. Therefore,
this
BIRD is proposed.
This new version contains only editorial changes and additions to the
current
text. Changes are indicated by "****" at the beginning of the changed
lines.
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STATEMENT OF THE RESOLVED SPECIFICATIONS:
Four new subparameters shall be introduced in the IBIS specification under
the [Model] keyword to provide means for a more detailed description for the
die capacitance. These new subparameters, C_comp_pullup, C_comp_pulldown,
C_comp_power, and C_comp_gnd are associated with the corresponding voltage
reference keywords, [Pullup Reference], [Pulldown Reference], [Power Clamp
Reference], and [GND Clamp Reference], respectively. This mechanism allows
the association of a specific capacitance between the I/O node and the four
possible supply nodes without disturbing the submodel syntax.
The syntax of these four new subparameters are identical to the existing
C_comp subparameter.
|===========================================================================
==
| Keyword: [Model]
| Required: Yes.
| Description: Used to define a model, and its attributes.
| Sub-Params: Model_type, Polarity, Enable, Vinl, Vinh, C_comp,
|**** C_comp_pullup, C_comp_pulldown, C_comp_power_clamp, and
|**** C_comp_gnd_clamp Vmeas, Cref, Rref, Vref
| Usage Rules: Each model type must begin with the keyword [Model]. The
| model name must match the one that is listed under a [Pin],
| [Model Selector] or [Series Pin Mapping] keyword and must
not
| contain more than 20 characters. A .ibs file must contain
| enough [Model] keywords to cover all of the model names
| specified under the [Pin], [Model Selector] and [Series Pin
| Mapping] keywords, except for those model names that use
| reserved words (POWER, GND and NC).
|
| Model_type must be one of the following:
|
| Input, Output, I/O, 3-state, Open_drain, I/O_open_drain,
| Open_sink, I/O_open_sink, Open_source, I/O_open_source,
| Input_ECL, Output_ECL, I/O_ECL, 3-state_ECL, Terminator,
| Series, and Series_switch.
|
| Special usage rules apply to the following. Some
definitions
| are included for clarification:
|
| Input These model types must have Vinl and Vinh
| I/O defined. If they are not defined, the
| I/O_open_drain parser issues a warning and the default
| I/O_open_sink values of Vinl = 0.8 V and Vinh = 2.0 V
are
| I/O_open_source assumed.
|
| Input_ECL These model types must have Vinl and Vinh
| I/O_ECL defined. If they are not defined, the
| parser issues a warning and the default
| values of Vinl = -1.475 V and Vinh =
| -1.165 V are assumed.
|
| Terminator This model type is an input-only model
| that can have analog loading effects on
the
| circuit being simulated but has no
digital
| logic thresholds. Examples of
Terminators
| are: capacitors, termination diodes, and
| pullup resistors.
|
| Output This model type indicates that an output
| always sources and/or sinks current and
| cannot be disabled.
|
| 3-state This model type indicates that an output
| can be disabled, i.e. put into a high
| impedance state.
|
| Open_sink These model types indicate that the
output
| Open_drain has an OPEN side (do not use the [Pullup]
| keyword, or if it must be used, set I =
| 0 mA for all voltages specified) and the
| output SINKS current. Open_drain model
| type is retained for backward
| compatibility.
|
| Open_source This model type indicates that the output
| has an OPEN side (do not use the
[Pulldown]
| keyword, or if it must be used, set I =
| 0 mA for all voltages specified) and the
| output SOURCES current.
|
| Input_ECL These model types specify that the model
| Output_ECL represents an ECL type logic that follows
| I/O_ECL different conventions for the [Pulldown]
| 3-state_ECL keyword.
|
| Series This model type is for series models that
| can be described by [R Series], [L
Series],
| [Rl Series], [C Series], [Lc Series],
| [Rc Series], [Series Current] and [Series
| MOSFET] keywords
|
| Series_switch This model type is for series switch
| models that can be described by [On],
| [Off], [R Series], [L Series], [Rl
Series],
| [C Series], [Lc Series], [Rc Series],
| [Series Current] and [Series MOSFET]
| keywords
|
|** The Model_type subparameter is required.
|****
|**** The C_comp subparameter is required only when C_comp_pullup,
|**** C_comp_pulldown, C_comp_power_clamp, and C_comp_gnd_clamp
are
|**** not present. If the C_comp subparameter is not present, at
|**** least one of the C_comp_pullup, C_comp_pulldown,
|**** C_comp_power_clamp, or C_comp_gnd_clamp subparameters is
|**** required. It is not illegal to include the C_comp
subparameter
|**** together with one or more of the remaining C_comp*
|**** subparameters, but in that case the simulator tool will have
to
|**** make a decision whether to use C_comp or the C_comp_pullup,
|**** C_comp_pulldown, C_comp_power_clamp, and C_comp_gnd_clamp
|**** subparameters. Under no circumstances should the simulator
use
|**** the value of C_comp simultaneously with the values of other
|**** C_comp* subparameters.
|
|**** C_comp_pullup, C_comp_pulldown, C_comp_power_clamp, and
|**** C_comp_gnd_clamp are intended to represent the parasitic
|**** capacitances of those structures who's I-V characteristics
|**** are described by the [Pullup], [Pulldown], [POWER Clamp] and
|**** [GND Clamp] I-V curves. For this reason, the simulator tool
|**** should generate a circuit netlist so that, if defined, each
of
|**** the C_comp* capacitors are connected parallel with their
|**** corresponding I-V curve generators, that is between the
signal
|**** pad and the nodes defined by the [Pullup Reference],
|**** [Pulldown Reference], [POWER Clamp Reference] and [GND Clamp
|**** Reference] keywords, or the [Voltage Range] keyword and GND.
|
|**** The C_comp and C_comp* parameters define die capacitance.
These
|**** values should not include the capacitance of the package.
|**** C_comp and C_comp* are allowed to use "NA" for the min and
max
|**** values only.
|
|**** The Polarity, Enable, Vinl, Vinh, Vmeas, Cref, Rref, and
Vref
|**** subparameters are optional. The Polarity subparameter can
be
| defined as either Non-Inverting or Inverting, and the Enable
| subparameter can be defined as either Active-High or
| Active-Low.
|
| The Cref and Rref subparameters correspond to the test load
| that the semiconductor vendor uses when specifying the
| propagation delay and/or output switching time of the model.
| The Vmeas subparameter is the reference voltage level that
the
| semiconductor vendor uses for the model. Include Cref,
Rref,
| Vref, and Vmeas information to facilitate board-level timing
| simulation. The assumed connections for Cref, Rref, and
Vref
| are shown in the following diagram:
|
| _________
| | |
| | |\ | Rref
| |Driver| \|------o----/\/\/\----o Vref
| | | /| |
| | |/ | === Cref
| |_________| |
| |
| GND
|
| Other Notes: A complete [Model] description normally contains the
following
| keywords: [Voltage Range], [Pullup], [Pulldown], [GND
Clamp],
| [POWER Clamp], and [Ramp]. A Terminator model uses one or
| more of the [Rgnd], [Rpower], [Rac], and [Cac]. However,
some
| models may have only a subset of these keywords. For
example,
| an input structure normally only needs the [Voltage Range],
| [GND Clamp], and possibly the [POWER Clamp] keywords. If
one
| or more of [Rgnd], [Rpower], [Rac], and [Cac] keywords are
| used, then the Model_type must be Terminator.
|---------------------------------------------------------------------------
-- | Signals CLK1, CLK2,... | Optional signal list, if desired [Model] Clockbuffer Model_type I/O Polarity Non-Inverting Enable Active-High Vinl = 0.8V | input logic "low" DC voltage, if any Vinh = 2.0V | input logic "high" DC voltage, if any Vmeas = 1.5V | Reference voltage for timing measurements Cref = 50pF | Timing specification test load capacitance value Rref = 500 | Timing specification test load resistance value Vref = 0 | Timing specification test load voltage | variable typ min max C_comp 12.0pF 10.0pF 15.0pF | |=========================================================================== == | [Model] Clockbuffer Model_type I/O Vinl = 0.8V | input logic "low" DC voltage, if any Vinh = 2.0V | input logic "high" DC voltage, if any | | variable typ min max C_comp_pullup 3.0pF 2.5pF 3.5pF C_comp_pulldown 2.0pF 1.5pF 2.5pF C_comp_power 1.0pF 0.5pF 1.5pF C_comp_gnd 1.0pF 0.5pF 1.5pF |The last paragraph of the Usage Rules section of the [Rising Waveform], [Falling Waveform] keyword description is changed as follows:
| All tables assume that the die capacitance is included. | Potential numerical problems associated with processing the |* data using the effective C_comp (C_comp or C_comp* as |* appropriate) for effective die capacitance may be handled |* differently among simulators.
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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION:
Needed information on where the distributed capacitance went, thus the addition of a paragraph to explain this.
Also, the names of two of the original subparameters, "C_comp_power" and "C_comp_gnd", were changed to "C_comp_power_clamp" and "C_comp_gnd_clamp" respectivly to better reflect their purpose. Some minor wording changes to the current draft text were also done.
Finally, updated a bit of text in the waveform keywords, per John Angulo's sugestion.
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ANY OTHER BACKGROUND INFORMATION:
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