Subject: [IBIS] BIRD74.6 EMI Parameters
From: deBurgh, Guy (guy_deburgh@mentorg.com)
Date: Fri Aug 08 2003 - 09:29:38 PDT
To the IBIS Committee.
BIRD 74 has been updated. Briefly the changes are:
1) Improved example, better clarification of syntax, and grammar
corrections.
The technical content has not been affected.
Guy de Burgh
Mentor Graphics
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BIRD ID#: 74.6
ISSUE TITLE: EMI Parameters
REQUESTER: Guy de Burgh, Mentor Graphics
DATE SUBMITTED: 3/19/02, 5/31/02, /9/16/02, 4/30/03, 5/21/03, 7/18/03,
8/08/03
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]
| [Pin EMI]
| [Pin Domain EMI]
|
| The following set of subparameters are defined:
|
| Domain
| Cpd
| C_Heatsink_gnd
| C_Heatsink_float
|
|===========================================================================
==
|
| Keyword: [Begin EMI Component]
| Required: No
| Description: Marks the beginning of the Component EMI parameters.
| Sub-Params: Domain, Cpd, C_Heatsink_gnd, C_Heatsink_float
|
| 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).
|
| The syntax for Domain is:
| Domain Domain_value
|
| Where Domain_value is an enumerated argument, and is one of:
| Digital, Analog, Digital_analog
|
| This subparameter is optional. If not entered the default
| is Digital.
|
| 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. Iccd is
| specified in units of mA/MHz.
|
| Cpd can be calculated from Iccd by the equation
| Cpd (nF) = Iccd (mA/MHz) / Vcc (V).
|
| The syntax for Cpd is:
| Cpd = capacitance_value
|
| The units of capacitance_value are Farads.
|
| This subparameter is optional. If not entered the default
| is 0.0F.
|
| C_Heatsink_Float and C_Heatsink_Gnd define the heatsink
| capacitance and connection conditions.
| C_Heatsink_Float indicates that the heatsink is floating,
| and C_Heatsink_Gnd indicates that the heatsink is grounded.
|
| Internal currents inside a (high speed) IC can be closely
| coupled onto a heatsink. As the heatsink is physically much
| larger than the IC silicon chip and bond wires it is a more
| efficient radiator. Knowing the capacitance of the heatsink
| the radiated electric field can be estimated.
|
| Only one of these subparameters can be defined. It is not
| legal to define both. It is legal to omit both. In this case
| it means that a heatsink is not present.
|
| The subparameter takes one argument: the heatsink
capacitance
|
| The syntax for Heatsink_cap is:
| C_Heatsink_float = capacitance_value
| C_Heatsink_gnd = capacitance_value
|
| The units for capacitance_value are Farads.
|
| This subparameter is optional. If not entered the default
| is that the component does not have a heatsink.
|
|===========================================================================
==
|
| Keyword: [End EMI Component]
| Required: No
| Description: Marks the end of the Component EMI parameters.
|
|===========================================================================
==
|
| Example:
|
[Begin EMI Component]
Domain Digital
Cpd = 6.4pF
C_Heatsink_gnd = 3.4pF
[End EMI Component]
|
|===========================================================================
==
|
| Keyword: [Pin EMI]
| Required: No
| Description: Specifies the EMI parameters for a Pin.
| Sub-Params: 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 second column is the domain name. This specifies the
clock
| domain for that pin. This is used by [Pin Domain EMI].
| The field should be set to NA if unused.
|
| The default for domain_name is that the percentage of power
| used is 100%.
|
| The third 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 maximum frequency is chosen as the
reference.
| The field should be set to NA if unused.
|
| The default for clock_div is 1.0
|
| Column length limits are:
| pin_name 5 characters max
| domain_name 20 characters max
| clock_div 5 characters max
|
| It is not a requirement to specify every pin. An undefined
| pin will default to 100% power usage for Domain_name,
| and 1.0 for clock_div.
|
|===========================================================================
=
|
| 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 second 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:
|
[Begin EMI Component]
Domain Digital
Cpd = 6.4pF
|
[Pin EMI] domain_name clock_div
4 MEM 0.5
5 MEM 0.5
7 NA 0.5 | domain_name defaults to 100%
8 RIOG NA | clock_div defaults to 1.0
14 CPU 1.0
15 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 Model] and [End EMI Model] keywords.
|
| The following set of keywords are defined:
|
| [Begin EMI Model]
| [End EMI Model]
|
| The following set of subparameters are defined:
|
| Model_emi_type
| Model_Domain
|
|===========================================================================
==
|
| Keyword: [Begin EMI Model]
| Required: No
| Description: Marks the beginning of the Model EMI parameters.
| Sub-Params: Model_emi_type, Domain
|
| Model_emi_type indicates whether the model (for this pin) is
a
| ferrite or not.
|
| The syntax for Model_emi_type is:
| Model_emi_type Model_emi_type_value
|
| Where Model_emi_type_value is an enumerated argument, and is
| one of:
| Ferrite, Not_a_ferrite
|
| If not entered (the default) the model is Not_a_ferrite.
|
| Model_Domain indicates whether the model is digital or
analog.
| This is only used if the [Component EMI] Domain is set to
| Digital_analog. If the [Component EMI] Domain is set to
| anything else Model_Domain is ignored.
|
| The syntax for Domain is:
| Model_Domain Domain_value
|
| Where Domain_value is one of:
| Digital, Analog
|
| If not entered the default is to use the [Component EMI]
| Domain setting and it's default.
|
|===========================================================================
==
|
| Keyword: [End EMI Model]
| Required: No
| Description: Marks the end of the Model EMI parameters.
|
|===========================================================================
==
|
|---------------------------------------------------------------------------
-- | [Begin EMI Model] Domain Analog 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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