Subject: [IBIS] BIRD74.3
From: deBurgh, Guy (guy_deburgh@mentorg.com)
Date: Wed Apr 30 2003 - 14:48:12 PDT
To the IBIS Committee.
BIRD 74 has been updated. Briefly the changes are:
1) Removed "Family" keyword
2) "Voltage Range" is now "Signal Swing"
3) Clock division added
4) Cleaned up syntax
Guy de Burgh
Mentor Graphics
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BIRD ID#: 74.3
ISSUE TITLE: EMI Parameters
REQUESTER: Guy de Burgh, Mentor Graphics
DATE SUBMITTED: April 30, 2003
DATE ACCEPTED BY IBIS OPEN FORUM: Pending
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STATEMENT OF THE ISSUE:
Additional parameters required for EMI analysis.
All these parameters are optional.
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**
STATEMENT OF THE RESOLVED SPECIFICATIONS:
The following changes are proposed:
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**
Changes and additions to the IBIS Specification are shown by the |* lines.
Examples are shown as they would be seen in a specification.
|===========================================================================
==
|===========================================================================
==
|
| Section 10
|
| E M I P A R A M E T E R S
|
|===========================================================================
==
|
| There are two sections here: one for a [Component] and one for a [Model].
|
|===========================================================================
==
|===========================================================================
==
|
| This section describes the structure of the EMI parameters under a
| top-level [Component] keyword. It is used to describe the EMI parameters
| associated with a [Component]. The parameters must be surrounded by
| the [Begin EMI Component] and [End EMI Component] keywords.
|
| The following set of keywords are defined:
|
| [Begin EMI Component]
| [End EMI Component]
| [Type]
| [Domain]
| [Cpd]
| [Signal Swing]
| [Pin EMI]
| [Pin Domain EMI]
|
|===========================================================================
==
|
| Keyword: [Begin EMI Component]
| Required: Yes
| Description: Marks the beginning of the Component EMI parameters.
| Sub-Params: Type, Domain, Cpd, Signal Swing, Heatsink Capacitance
|
|===========================================================================
==
|
| Keyword: [Type]
| Required: No
| Description: Type indicates whether the component is a connector.
| This identifies I/O signals (which act as monopole
| antennas).
|
| Usage Rules: It is one of:
| Active, Connector
|
| If not entered the default is Active.
|
|===========================================================================
==
|
| Keyword: [Domain]
| Required: No
| Description: Domain indicates whether the component is a digital, analog
| or part digital part analog. Analog circuits are more
| susceptible to low-level noise. Analog circuits operate at
| very low signal levels (mV or uV) and can contain high gain
| amplifiers. In contrast, digital circuits operate at
| relatively large signal levels (compared to analog
circuits).
|
| Usage Rules: It is one of:
| Digital, Analog, Digital_analog
|
| If not entered the default is Digital.
|
|===========================================================================
==
|
| Keyword: [Cpd]
| Required: No
| Description: Cpd is the power dissipation capacitance parameter.
| Cpd (Power Dissipation Capacitance) is the internal
parasitic
| capacitance (e.g., gate-to-source and gate-to-drain
| capacitance) plus the equivalent capacitance associated with
| the through currents when both transistors (n-channel and
| p-channel) are momentarily conducting.
|
| It is typically for CMOS devices, and helps provide a more
| accurate estimation of the power bus current, and therefore
| the noise voltage on the power bus. Knowing the high
frequency
| noise on the power bus (due to switching of digital
circuits)
| the radiation can be calculated.
|
| Sometimes Iccd (Dynamic power supply current) is found in
| databooks. It is normally given for FACT families. Cpd can
be
| calculated from Iccd by the equation Cpd = Iccd / Vcc.
|
| Usage Rules: The syntax for Cpd is:
| Cpd
|
| The units are Farads.
|
| If not entered the default is 0.0F.
|
|===========================================================================
==
|
| Keyword: [Signal Swing]
| Required: No
| Description: This parameter describes the voltage range, or signal swing,
| of typical driver or bi-directional output. Note that these
| voltages are not necessarily equal to the power rails.
| E.g. for ECL the power rails are 0V and 3.3V, but the signal
| swing is 1.625V to 2.375V.
|
| Usage Rules: The syntax for Signal Swing is:
| Vmin Vmax
|
| The units are Volts.
|
| If not entered the default is [Voltage Range].
|
|===========================================================================
==
|
| Keyword: [Heatsink Capacitance]
| Required: No
| Description: Current flowing on a return plane on a PCB induces a common
| mode voltage capable of driving current onto heatsinks and
| cables. If we know the capacitance between the heatsink and
| the cable the radiated electric field can be calculated.
| If this parameter is defined then a Heatsink is present.
| If this parameter is not defined then the component does not
| have a heatsink.
|
| Usage Rules: The syntax for Heatsink capacitance is:
| Heatsink_cap
|
| The units are Farads.
|
| If not entered the default is the component does not have
| a heatsink.
|
|===========================================================================
==
|
| Example:
|
[Component] ecl_component
.
.
.
[Begin EMI Component]
Type Active
Domain Digital
Cpd = 6.4pF
Signal_Swing 1.625 2.375
Heatsink_cap = 3.4pF
[End EMI Component]
|
|===========================================================================
==
|
| Keyword: [Pin EMI]
| Required: No
| Description: Specifies the EMI parameters for a Pin.
| Sub-Params: cspec_name, domain_name, clock_div
| Usage Rules: Each line must contain three columns.
| The first column must contain the pin name. This pin name
| must match a pin name in the [Pin] keyword. (The pin name
| is the first column in the [Pin] record.)
|
| The cspec_name represents a user definable specification
| name that must have a corresponding model name listed in the
| [Model EMI] keyword. This is used when the pin is a
connector
| pin. The field can be left empty, or set to NA, if unused.
|
| The third column is the domain name. This specifies the
clock
| domain for that pin. This is used by [Pin Domain EMI].
| The field can be left empty, or set to NA, if unused.
|
| The fourth column is the clock division. This is the ratio
| of the frequency at this pin to the reference pin. The
| reference pin is always set to "1.0". The ratio is a
floating
| point number. The choice of the reference in does not matter
| as this information is pin to pin ratios. It is suggested
that
| the pin with the dominant frequency is chosen as the
reference.
| The field can be left empty, or set to NA, if unused.
|
| Column length limits are:
| pin_name 5 characters max
| cspec_name 20 characters max
| domain_name 20 characters max
| clock_div 5 characters max
|
|===========================================================================
=
|
| Keyword: [Pin Domain EMI]
| Required: No
| Description: Specifies the percentage of power used in each clock domain.
| Sub-Params: percentage
| Usage Rules: Each line must contain two columns.
| The first column must contain the domain_name. This name
must
| match a domain name in the [Pin EMI] keyword. (The domain
| name is the third column in that record.)
|
| The percentage represents a user definable percentage of the
| power used by that domain. It is an integer in the range
| 0 < percentage =< 100
|
| Column length limits are:
| domain_name 20 characters max
| percentage 5 characters max
|
|===========================================================================
==
|
| Example:
|
[Component] ecl_component
.
.
.
[Begin EMI Component]
Type Active
Domain Digital
Cpd = 6.4pF
|
[Pin EMI] cspec_name domain_name clock_div
1 unshielded NA
4 mem_pin MEM 0.5
5 mem_pin MEM 0.5
10 grounded NA
14 CPU 1.0
15 shielded RIOG 0.5
|
[Pin Domain EMI] percentage
CPU 40
MEM 30
RIOG 30
|
[End EMI Component]
|
|===========================================================================
==
|===========================================================================
==
|
| This section describes the structure of the EMI parameters under a
| top-level [Model] keyword. It is used to describe the EMI parameters
| associated with a [Model]. The parameters must be surrounded by
| the [Begin EMI] and [End EMI] keywords.
|
| The following set of keywords are defined:
|
| [Begin EMI Model]
| [End EMI Model]
| [Model EMI]
|
|===========================================================================
==
|
| Keyword: [Begin EMI Model]
| Required: Yes
| Description: Marks the beginning of the Model EMI parameters.
|
|===========================================================================
==
|
| Keyword: [End EMI Model]
| Required: Yes
| Description: Marks the end of the Model EMI parameters.
|
|===========================================================================
==
|
| Keyword: [Model EMI]
| Required: No
| Description: Used to define EMI parameters for a model.
| Sub-Params: Model_emi_type, Domain, Con_spec
| Usage Rules: Each model type must begin with the keyword [Model EMI].
The
| model name must match the one that is listed under a
| cspec_name in [Pin EMI],
|
| Model_emi_type can only be set to Ferrite. This indicates
| that the model is a ferrite. If not entered (the default)
| the model is not a ferrite.
|
| Domain indicates whether the model is a digital or analog.
| It is one of:
| Digital, Analog
|
| This is only required if the [Component EMI] Domain is set
to
| Digital_analog.
|
| If not entered the default is to use the [Component EMI]
| Domain setting and its default.
|
| Con_spec indicates whether the pin is Unshielded (normally
| connected), Shielded (ground pins provide shield),
| Shielded_pwr (power pins provide shield),
| Con_to_shield (pin connected to connector shell), or
| Ferrite (has a ferrite filter).
|
| In addition the pin can have explicit filter capacitance.
|
| These parameters are used to calculate an antenna impedance
| for the pin.
|
| The syntax is:
| Con_spec attribute filter_cap
|
| where attribute is one of:
| Unshielded, Shielded, Shielded_pwr, Con_to_shield,
Ferrite.
|
| filter_cap is the filter capacitance in Farads. It is
optional
| and it should be set to NA if not used.
|
|---------------------------------------------------------------------------
-- | [Model] modelname . . . [Begin EMI Model] | [Model EMI] grounded Con_spec Shielded 7.0pF | [Model EMI] mem_pin Model_emi_type Ferrite | [End EMI Model] | **************************************************************************** **ANALYSIS PATH/DATA THAT LED TO SPECIFICATION:
EMI is becoming increasingly important in PCB design. EMI simulation is not an exact science. The problem is too complicated for today's computers. However being able to identify which signals radiate more than others (relatively), and showing where the energy flows in a system does help in identifying potential EMI problems. No longer requiring absolute accuracy, but requiring relative accuracy, makes the analysis considerably easier, and possible. The parameters specified here are chosen for that purpose, and have been specifically chosen as they are readily available in data books in order to make it easier to create models.
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ANY OTHER BACKGROUND INFORMATION:
Presentations on this topic were given at the IBIS Summit Meeting at DAC on June 21, 2001, and at DesignCon on January 28, 2002.
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