Subject: [IBIS] BIRD74.2 - EMI Parameters
From: Ross, Bob (bob_ross@mentorg.com)
Date: Mon Sep 16 2002 - 11:55:28 PDT
To All:
Guy de Burgh is issuing BIRD74.2 below:
Bob Ross
Mentor Graphics
----------
To the IBIS Committee.
BIRD 74 has been updated. Briefly the changes are:
1) Instead on interspersing the EMI parameters throughout the specification
a chapter containing all the EMI parameters have been created.
A new chapter, Section 10, for these parameters has been created.
2) Begin/End keywords are used to bound the parameters.
Guy de Burgh
Mentor Graphics
******************************************************************************
******************************************************************************
BIRD ID#: 74.2
ISSUE TITLE: EMI Parameters
REQUESTER: Guy de Burgh, Mentor Graphics
DATE SUBMITTED: March 19, 2002, May 31, 2002, September 16, 2002
DATE ACCEPTED BY IBIS OPEN FORUM: Pending
******************************************************************************
******************************************************************************
STATEMENT OF THE ISSUE:
Additional parameters required for EMI analysis.
All these parameters are optional.
******************************************************************************
STATEMENT OF THE RESOLVED SPECIFICATIONS:
The following changes are proposed:
******************************************************************************
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]
| [Family]
| [Cpd]
| [Pin EMI]
| [Pin Domain EMI]
|
|=============================================================================
|
| Keyword: [Begin EMI Component]
| Required: Yes
| Description: Marks the beginning of the Component EMI parameters.
| Sub-Params: Type, Domain, Family, Cpd
|
|=============================================================================
|
| 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: [Family]
| Required: No
| Description: Family describes the logic family of the component.
| This parameter is used so that reasonable assumptions about
| missing information can be made when an incomplete model
| specification is used. Typical missing information can be
| Input impedance, Source impedance and Maximum transient
| switching current.
|
| Even if this information is already available the logic family
| adds extra information. For example, unused floating inputs on
| a high input impedance device is likely to pick up noise.
| In addition, if the device is CMOS, an unused gate whose
| inputs are floating may bias itself into the linear region.
| This will increase the dc current drawn by the circuit.
|
| Usage Rules: It is one of:
| UNDEF, TTL, CMOS, ECL
|
| TTL, CMOS, and ECL can be used in a similar manner as that
| ust described for CMOS. UNDEF is used to disable any family
| specific algorithms.
|
| If not entered the default is UNDEF.
|
|=============================================================================
|
| 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.
|
|=============================================================================
|
| Keyword: [End EMI Component]
| Required: Yes
| Description: Marks the end of the Component EMI parameters.
|
|=============================================================================
|
| Example:
|
[Component] ecl_component
.
.
.
[Begin EMI Component]
Type Active
Domain Digital
Family ECL
Cpd = 6.4pF
[End EMI Component]
|
|=============================================================================
|
| Keyword: [Pin EMI]
| Required: No
| Description: Specifies the EMI parameters for a Pin.
| Sub-Params: cspec_name
| 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 third column is the domain name. This specifies the clock
| domain for that pin. This is used by [Pin Domain EMI].
|
| Column length limits are:
| pin_name 5 characters max
| cspec_name 20 characters max
| domain_name 20 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.
|
| Column length limits are:
| domain_name 20 characters max
| percentage 5 characters max
|
|=============================================================================
|
| Example:
|
[Component] ecl_component
.
.
.
[Begin EMI Component]
Type Active
Domain Digital
Family ECL
Cpd 6.4pF
|
[Pin EMI] cspec_name domain_name
1 unshielded NA
4 a_pin MEM
5 b_pin MEM
10 grounded
14 shielded CPU
15 shielded RIOG
|
[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] a_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.
******************************************************************************
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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