Buffer Issue Resolution Document (BIRD) BIRD ID#: 111.3 ISSUE TITLE: Extended Usage of External Series Components in EBDs REQUESTOR: Michael Schaeder, Zuken DATE SUBMITTED: July 1, 2008 DATE REVISED: September 18, 2008, February 10, 2009, April 3, 2009 DATE ACCEPTED BY IBIS OPEN FORUM: April 24, 2009 **************************************************************************** **************************************************************************** STATEMENT OF THE ISSUE: The current EBD specification states that discrete Series Components can be defined by writing two back to back node statements that reference the same component. In this case, both ends of the discrete two terminal component must be contained in a single path description. Connecting two separate path descriptions with a series component is not allowed. However, many EBDs available in industry also use external Series Components in EBDs that connect two separate [Path Description]s, or two branches in a single [Path Description], to define differential resistors and capacitor terminations. These EBDs can have differential pin pairs on the separate [Path Description]s or two branches of a single [Path Description]. Such EBDs already pass the IBIS Golden Parser without any problem. By allowing the changes specified in this BIRD, EDA tools will be able to use [Diff Pin] data in the pins connected directly or indirectly to the separate branches separate [Path Description]s to correctly generate interconnect circuits for differentials in EBD files. Therefore the current EBD specification should be modified such that it is allowed to insert Series Components between two branches of a single path description or between two separate path descriptions. **************************************************************************** STATEMENT OF THE RESOLVED SPECIFICATIONS: Changes are noted in the relevant sections below by |* and |*** lines. Replace the following text of the "Dealing With Series Elements" paragraph of the [Path Description] keyword in section 8 (from the 4.2/5.0a spec): | A discrete series R or L component can be included in a path | description by defining a section with Len=0 and the proper R | or L value. A discrete series component can also be included | in a path description by writing two back to back node | statements that reference the same component (see the example | below). Note that both ends of a discrete, two terminal | component MUST be contained in a single [Path Description]. | Connecting two separate [Path Description]s with a series | component is not allowed. with: | A discrete series R or L component can be included in a path | description by defining a section with Len=0 and the proper R | or L value. A discrete series component can also be included |* by writing node statements that reference the same component. |* This can be done as two back to back node statements for a |* series component within a single [Path Description]. It is |* also allowed to insert a series component between two branches |* of a single [Path Description], or even between two separate |* [Path Description]s (see the examples below). |*** |*** When a series component is modeled with node statements and |*** reference_designator.pin arguments, the referenced pin models |*** can be Series or Series_switch. The following models are |*** supported: [R Series], [L Series], [C Series], [Rl Series], |*** [Lc Series], [Rc Series], [Series Current], and |*** [Series MOSFET]. |*** Two paragraphs in BIRD111.1 were removed as noted in the Analysis |*** Section Add the following examples: | A path including series passive components (C17, R21) | between branches forming a differential termination | | [Path Description] CLK Pin 137 Len=1.1 L=1n C=0.4p / Node C17.1 | Pin 1 of Series C17 Len=1.2 L=1n C=0.4p / Node R21.1 | Series R21 Pin 1 and 2 connections Node R21.2 Len=1.3 L=1n C=0.4p / Node C17.2 | Pin 2 of Series C17 Len=1.4 L=1n C=0.4p Pin 138 | | | _______ _______ | 137 <-----O_______O----+----O_______O-----+ | | Len=1.1 | Len=1.2 | | | +--+--+ +--+--+ | | |Pin 1| |Pin 1| | | | | | | | | | C17 | | R21 | | | | | | | | | |Pin 2| |Pin 2| | | +--+--+ +--+--+ | | _______ | _______ | | 138 <-----O_______O----+----O_______O-----+ | | Len=1.4 Len=1.3 | | | | Two paths connected by series resistors (R8, R9) used as | differential termination between components | [Path Description] DP+ Pin 20 Len=1 L=1n C=0.4p / Fork Len=1.1 L=1n C=0.4p / Fork Node P8.D7 Endfork Len=1.2 L=1n C=0.4p / Node R8.1 | Pin 1 of Series R8 Endfork Len=1.3 L=1n C=0.4p / Fork Len=1.4 L=1n C=0.4p / Node P8.D5 Endfork Len=1.5 L=1n C=0.4p / Node R9.1 | Pin 1 of Series R9 | ... Other Path(s) [Path Description] DP- Pin 22 Len=1 L=1n C=0.4p / Fork Len=1.1 L=1n C=0.4p / Fork Node Q8.D7 Endfork Len=1.2 L=1n C=0.4p / Node R8.2 | Pin 2 of Series R8 Endfork Len=1.3 L=1n C=0.4p / Fork Len=1.4 L=1n C=0.4p / Node Q8.D5 Endfork Len=1.5 L=1n C=0.4p / Node R9.2 | Pin 2 of Series R9 | | | _______ _______ _______ | 20 <-------O_______O----+----O_______O----+----O_______O--+ | | Len=1 | Len=1.1 | Len1.2 | | | _______ | | | | | +--O_______O----+ | | | | | Len=1.3 +-----+ +--+--+ | | | | _______ |Pin | |Pin | | | | +--O_______O-------+ | | | | | | | Len=1.4 |P8.D5| |P8.D7| | | | | _______ +-----+ +-----+ | | | +--O_______O---+ | | | Len=1.5 | | | | +--+--+ +--+--+ | | |Pin 1| |Pin 1| | | | | | | | | | R9 | | R8 | | | . . | | . . | | . . | | | R9 | | R8 | | | | | | | | | |Pin 2| |Pin 2| | | +--+--+ +--+--+ | | _______ | | | | +--O_______O---+ | | | | Len=1.5 +-----+ +-----+ | | | | _______ |Pin | |Pin | | | | +--O_______O-------+ | | | | | | | Len=1.4 |Q8.D5| |Q8.D7| | | | | _______ +-----+ +--+--+ | | | +--O_______O----+ | | | | Len=1.3 | | | | | _______ | _______ | _______ | | 22 <-------O_______O----+----O_______O----+----O_______O--+ | | Len=1 Len=1.1 Len=1.2 | **************************************************************************** ANALYSIS PATH/DATA THAT LED TO SPECIFICATION: Today there are some EBD models available that use series components connecting separate path descriptions in the way it is outlined above. Typical applications areas are DIMM modules and differential termination networks. Since this usage of EBD description capabilities is required to enable these kinds of modeling the IBIS Standard should be updated to reflect it's usage in the industry. The new definition outlined above is most suitable to define differential pair termination in the most flexible way. As the IBIS Golden Parser already accepts this EBD syntax it need not to be changed. Applications need to be extended in order to consider series components used this way. BIRD111.1 Example syntax corrected to include 'Node' for each internal node. Also, transmission line connections were added since direct Node to Node syntax for the simplified example is only supported for direct Series connections through the device (This is also extended to differential pins). IBIS meeting discussion on July 18 added the original concern that each path be self-contained for easier net-listing. The concern was that tools might get lost when bridging paths through Series or Series_switch components, or components not connected via differential pin assignments. Also, after some e-mails, there was concern that this could extend to include differential pins. While not mentioned, this capability already exists since the distinct single-ended notes in each path could be pins associated by the [Diff Pin] keyword - thus be considered differential. So, like series elements, the Node Node syntax is extended to include differential pins Note, an IBIS file might include pin-pairs with both series pins for on-die differential terminators and differential pin models. Model names are not part of the [Reference Designator Map]. For example, from the mapping below, the specific set of models assigned to each pin are not known externally. This BIRD allows all combinations, but does require the tool to actually search the IBIS file, particularly the [Diff Pin] and [Series Pin Mapping] keywords to determine if there are any connections between pin-pairs documented. In most cases, there will just be the single-ended pins. [Reference Designator Map] | Ref Des File name Component name u23 r.ibs series_r | two-pin series R u24 diff.ibs diff_pin_pair | two-pin diff. pair u25 diff_ser_odt.ibs diff_ser_pin_pair | two-pin diff with odt u26 single.ibs single_ended | any one-pin single-ended | buffer u27 combined.ibs one_component | complete multiple pin | model with any or all of | the above combinations This BIRD does not extend to .ebd files as reference designators. It is theoretically possible to also trace through all levels of .ebd call down to a .ibs file, the tool support allowing for infinite levels of recursion might be unreliable. This applies to the existing syntax, so no statement is added in BIRD111.1. Also note, the two examples actually have internal loops with paths in parallel. If this were not the case, the existing syntax of Node Node could be used by a different ordering of the Fork/Endfork sequence. Then this BIRD would not be needed. BIRD111.2 Reference to how EDA tools can use this information in conjunction with differential pin information in associated IBIS files have been removed. This removed text in BIRD111.1 is shown below for reference. |** |** It is also allowed to insert a differential pin pairs between |** two branches of a single [Path Description], or even between |** two separate [Path Description]s |** |** In order to process discrete series components and differential |** pin pairs thoroughly, the IBIS component named in the [Reference |** Designator Map] for .ibs-files needs to be evaluated, and [Series |** Pin Mapping] and [Diff Pin] statements need to be considered. |** Since series elements and diff pairs are not known in advance, |** evaluation has to be done for every Node in an EBD path |** description. To deal with a suggestion by Walter Katz, the Statement of the Issue is modified to discuss [Diff Pin]: --- Delete this paragraph "However, many EBDs available in industry also use external Series Components in EBDs that connect two separate paths, mainly to define differential termination resistors. Such EBDs also pass the IBIS Golden Parser without any problem." Replace with these paragraphs: "However, many EBDs available in industry also use external Series Components in EBDs that connect two separate [Path Description]s, or two branches in a single [Path Description], to define differential resistors and capacitor terminations. These EBDs can have differential pin pairs on the separate [Path Description]s or two branches of a single [Path Description]. Such EBDs already pass the IBIS Golden Parser without any problem."" "By allowing the changes specified in this BIRD, EDA tools will be able to use [Diff Pin] data in the pins connected directly or indirectly to the separate branches separate [Path Description]s to correctly generate interconnect circuits for differentials in EBD files." --- While there exists some technical ambiguity, there is no direct restriction regarding the above statements. For practical purposes, the differential resistor is the of primary interest, and BIRD111.2 moves forward for this specific addition. BIRD111.3 The additional paragraph designated by |*** lines is added to clarify that all types of Series and Series_switch model types are permitted when adding a series element by nodes and the reference_designator.pin. The models are listed. This is in response for more clarification at the March 13, 2009 IBIS meeting. **************************************************************************** ANY OTHER BACKGROUND INFORMATION: ****************************************************************************