****************************************************************************** ****************************************************************************** BIRD ID#: 104 ISSUE TITLE: [Model Spec] DDR2 Overshoot/Undershoot Parameters REQUESTER: Randy Wolff, Micron Technology, Inc. DATE SUBMITTED: April 21, 2006 DATE ACCEPTED BY IBIS OPEN FORUM: PENDING ****************************************************************************** ****************************************************************************** STATEMENT OF THE ISSUE: The JEDEC DDR2 SDRAM Specification (JESD79-2A) specifies AC overshoot and undershoot in terms of a maximum area above or below specific voltage thresholds. A maximum overshoot/undershoot amplitude is also defined. The parameters available for [Model Spec] do not provide a way to check for violations of this overshoot/undershoot condition as calculated by area. The dynamic overshoot/undershoot parameters can specify time and maximum voltage, but these are not adequate to define an area in terms of V-s. This BIRD proposes adding four new parameters to the IBIS specification under [Model Spec] that will give EDA software the conditions necessary to check for overshoot/undershoot violations on DDR2 SDRAM devices and issue warnings. ****************************************************************************** STATEMENT OF THE RESOLVED SPECIFICATIONS: All changes, with the exception of spacing and line break adjustments, are shown with |*. |***************************************************************************** |* ORIGINAL [Model Spec] TEXT |***************************************************************************** |============================================================================= | Keyword: [Model Spec] | Required: No | Sub-Params: Vinh, Vinl, Vinh+, Vinh-, Vinl+, Vinl-, S_overshoot_high, | S_overshoot_low, D_overshoot_high, D_overshoot_low, | D_overshoot_time, Pulse_high, Pulse_low, Pulse_time, Vmeas, | Vref, Cref, Rref, Cref_rising, Cref_falling, Rref_rising, | Rref_falling, Vref_rising, Vref_falling, Vmeas_rising, | Vmeas_falling, Rref_diff, Cref_diff | Description: The [Model Spec] keyword defines four columns under which | specification subparameters are defined. | | The following subparameters are defined: | Vinh Input voltage threshold high | Vinl Input voltage threshold low | Vinh+ Hysteresis threshold high max Vt+ | Vinh- Hysteresis threshold high min Vt+ | Vinl+ Hysteresis threshold low max Vt- | Vinl- Hysteresis threshold low min Vt- | S_overshoot_high Static overshoot high voltage | S_overshoot_low Static overshoot low voltage | D_overshoot_high Dynamic overshoot high voltage | D_overshoot_low Dynamic overshoot low voltage | D_overshoot_time Dynamic overshoot time | Pulse_high Pulse immunity high voltage | Pulse_low Pulse immunity low voltage | Pulse_time Pulse immunity time | Vmeas Measurement voltage for timing measurements | Vref Timing specification test load voltage | Cref Timing specification capacitive load | Rref Timing specification resistance load | Cref_rising Timing specification capacitive load for | rising edges | Cref_falling Timing specification capacitive load for | falling edges | Rref_rising Timing specification resistance load for | rising edges | Rref_falling Timing specification resistance load for | falling edges | Vref_rising Timing specification test load voltage for | rising edges | Vref_falling Timing specification test load voltage for | falling edges | Vmeas_rising Measurement voltage for rising edge timing | measurements | Vmeas_falling Measurement voltage for falling edge timing | measurements | Rref_diff Timing specification differential | resistance load | Cref_diff Timing specification differential | capacitive load | | Usage Rules: [Model Spec] must follow all other subparameters under the | [Model] keyword. | | For each subparameter contained in the first column, the | remaining three hold its typical, minimum and maximum values. | The entries of typical, minimum and maximum must be placed on | a single line and must be separated by at least one white | space. All four columns are required under the [Model Spec] | keyword. However, data is required only in the typical | column. If minimum and/or maximum values are not available, | the reserved word "NA" must be used indicating the typical | value by default. | | The minimum and maximum values are used for specifications | subparameter values that may track the min and max operation | conditions of the [Model]. Usually it is related to the | Voltage Range settings. | | Unless noted below, no subparameter requires having present | any other subparameter. | | Vinh, Vinl rules: | | The threshold subparameter lines provide additional min and | max column values, if needed. The typ column values are still | required and would be expected to override the Vinh and Vinl | subparameter values specified elsewhere. Note: the syntax | rule that require inserting Vinh and Vinl under models remains | unchanged even if the values are defined under the [Model | Spec] keyword. | | Vinh+, Vinh-, Vinl+, Vinl- rules: | | The four hysteresis subparameters (used for Schmitt trigger | inputs for defining two thresholds for the rising edges and | two thresholds for falling edges) must all be defined before | independent input thresholds for rising and falling edges of | the hysteresis threshold rules become effective. Otherwise | the standard threshold subparameters remain in effect. The | hysteresis thresholds shall be at the Vinh+ and Vinh- values | for a low-to-high transition, and at the Vinl+ and Vinl- | values for a high-to-low transition. | | | | | Receiver Voltage with Hysteresis Thresholds | | | | | | Rising Edge Falling Edge | | Switching Region oo o Switching Region | | | o oo ooooooooo | | | V o o | | Vinh+ - - - - - - - - - - x o | | Vinh- - - - - - - - - - x o | | | o o | | | o o | | | o oV | Vinl+ - - - - - - - o - - - - - - - - - - - - - - - - - x | Vinl- - - - - - - - o - - - - - - - - - - - - - - - - - x | | o o | | o o | |oooooo-----------------------------------------------------oooooooo | | Time --> | | S_overshoot_high, S_overshoot_low rules: | | The static overshoot subparameters provide the DC voltage | values for which the model is no longer guaranteed to function | correctly. Typically these are voltages that would cause the | physical component to be destroyed. | | D_overshoot_high, D_overshoot_low, D_overshoot_time rules: | | The dynamic overshoot values provide a time window during | which the overshoot may exceed the static overshoot limits | but be below the dynamic overshoot limits. D_overshoot_time | is required for dynamic overshoot testing. In addition, if | D_overshoot_high is specified, then S_overshoot_high is | necessary for testing beyond the static limit. Similarly, if | D_overshoot_low is specified, then S_overshoot_low is | necessary for testing beyond the static limit. | | | | | Receiver Voltage with Static and Dynamic Overshoot Limits | | | | | | D_overshoot_time ->| |<- | | | | | D_overshoot_high - - - - - - -+ - - -+ | | | oo | Passes - Does Not Exceed Bounds | | |o o | | S_overshoot_high - - - - - - -x o +- - - - - - - - - - - - - - - - - - - | | o o ooooooooo | | o o o | | o o | | o o | | o o | | o o | | o o | | o o Fails - | | o o Exceeds Bounds | | o o | | | | | o o V V V | |oooooo-------------------------------------------o---------o---oooo | S_overshoot_low - - - - - - - - - - - - - - - - - - - - - x +x x x - - | | |o x x | | | o o| | D_overshoot_low - - - - - - - - - - - - - - - - - - - - - + -x x-+ | | | x | | D_overshoot_time ->| |<- | | Time --> | | Pulse_high, Pulse_low, Pulse_time rules: | | The pulse immunity values provide a time window during which | a rising pulse may exceed the nearest threshold value but | be below the pulse voltage value and still not cause the | input to switch. Pulse_time is required for pulse immunity | testing. A rising response is tested only if Pulse_high is | specified. Similarly, a falling response is tested only if | Pulse_low is specified. The rising response may exceed the | Vinl value, but remain below the Pulse_high value. | | Similarly, the falling response may drop below the Vinh value, | but remain above the Pulse_low value. In either case the | input is regarded as immune to switching if the responses | are within these extended windows. If the hysteresis | thresholds are defined, then the rising response shall use | Vinh- as the reference voltage, and the falling response shall | use Vinl+ as the reference voltage. | | | | | Receiver Voltage with Pulse Immunity Thresholds | | | | | | Switching No Switching | | | | | | | oo o | Switching | | | o oo ooooooooo | | | | | o o | | | | V o o V oooV | Vinh - - - - - - - - - - x - - - - - - - - - - - - - x o + -x | | Pulse_time ->| o |<- |ooo | o | Pulse_high - - - - - + o - + Pulse_low - + - - + o | | |o | Pulse_time ->| |<- o | Vinl - - - - - - - - x + - - - - - - - - - - - - - - - - - - x | | o o | | o o | | o o | |oooooo------------------------------------------------------------o | | Time --> | | Vmeas, Vref, Cref, Rref rules: | | The Vmeas, Vref, Cref and Rref values under the [Model Spec] | keyword override their respective values entered elsewhere. | Note that a Vmeas, Vref, Cref or Rref subparameters may not be | used if its edge specific version (*_rising or *_falling) is | used. | | Cref_rising, Cref_falling, Rref_rising, Rref_falling, | Vref_rising, Vref_falling, Vmeas_rising, Vmeas_falling rules: | | Use these subparameters when specifying separate timing test | loads and voltages for rising and falling edges. If one | 'rising' or 'falling' subparameter is used, then the | corresponding 'rising' or 'falling' subparameter must be | present. The values listed in these subparameters override | any corresponding Cref, Vref, Rref or Vmeas values entered | elsewhere. | | Rref_diff, Cref_diff rules: | | The Rref_diff and Creff_diff values under the [Model Spec] | keyword override their respective values entered elsewhere. | These subparameters are used only when the model is referenced | by the [Diff Pin] keyword. These follow the same rules as | the corresponding subparameters documented under the [Model] | keyword. See Section 6b for more discussion on true and | single-ended differential operation. |----------------------------------------------------------------------------- [Model Spec] | Subparameter typ min max | | Thresholds | Vinh 3.5 3.15 3.85 | 70% of Vcc Vinl 1.5 1.35 1.65 | 30% of Vcc | | Vinh 3.835 3.335 4.335 | Offset from Vcc | Vinl 3.525 3.025 4.025 | for PECL | | Hysteresis | Vinh+ 2.0 NA NA | Overrides the Vinh- 1.6 NA NA | thresholds Vinl+ 1.1 NA NA Vinl- 0.6 NA NA | All 4 are required | | Overshoot | S_overshoot_high 5.5 5.0 6.0 | Static overshoot S_overshoot_low -0.5 NA NA D_overshoot_high 6.0 5.5 6.5 | Dynamic overshoot D_overshoot_low -1.0 -1.0 -1.0 | requires | | D_overshoot_time D_overshoot_time 20n 20n 20n | & static overshoot | | Pulse Immunity | Pulse_high 3V NA NA | Pulse immunity Pulse_low 0 NA NA | requires Pulse_time 3n NA NA | Pulse_time | | Timing Thresholds | Vmeas 3.68 3.18 4.68 | A 5 volt PECL | | example | | Timing test load voltage reference example | Vref 1.25 1.15 1.35 | An SSTL-2 example | | | Rising and falling timing test load example (values from PCI-X | specification) | Cref_falling 10p 10p 10p Cref_rising 10p 10p 10p Rref_rising 25 500 25 | typ value not specified Rref_falling 25 500 25 | typ value not specified Vref_rising 0 1.5 0 Vref_falling 3.3 1.5 3.6 Vmeas_rising 0.941 0.885 1.026 | vmeas = 0.285(vcc) Vmeas_falling 2.0295 1.845 2.214 | vmeas = 0.615(vcc) | | Differential timing test load for true or single-ended differential model | Rref_diff 100 90 110 Cref_diff 5pF NA NA | |***************************************************************************** |* END ORIGINAL TEXT |***************************************************************************** |***************************************************************************** |* NEW TEXT |***************************************************************************** |============================================================================= | Keyword: [Model Spec] | Required: No | Sub-Params: Vinh, Vinl, Vinh+, Vinh-, Vinl+, Vinl-, S_overshoot_high, | S_overshoot_low, D_overshoot_high, D_overshoot_low, |* D_overshoot_time, D_overshoot_area_h, D_overshoot_area_l, |* D_overshoot_ampl_h, D_overshoot_ampl_l, Pulse_high, Pulse_low, |* Pulse_time, Vmeas, Vref, Cref, Rref, Cref_rising, Cref_falling, |* Rref_rising, Rref_falling, Vref_rising, Vref_falling, |* Vmeas_rising, Vmeas_falling, Rref_diff, Cref_diff | | Description: The [Model Spec] keyword defines four columns under which | specification subparameters are defined. | | The following subparameters are defined: | Vinh Input voltage threshold high | Vinl Input voltage threshold low | Vinh+ Hysteresis threshold high max Vt+ | Vinh- Hysteresis threshold high min Vt+ | Vinl+ Hysteresis threshold low max Vt- | Vinl- Hysteresis threshold low min Vt- | S_overshoot_high Static overshoot high voltage | S_overshoot_low Static overshoot low voltage | D_overshoot_high Dynamic overshoot high voltage | D_overshoot_low Dynamic overshoot low voltage | D_overshoot_time Dynamic overshoot time |* D_overshoot_area_h Dynamic overshoot high area (in V-s) |* D_overshoot_area_l Dynamic overshoot low area (in V-s) |* D_overshoot_ampl_h Dynamic overshoot high max amplitude |* D_overshoot_ampl_l Dynamic overshoot low max amplitude | Pulse_high Pulse immunity high voltage | Pulse_low Pulse immunity low voltage | Pulse_time Pulse immunity time | Vmeas Measurement voltage for timing measurements | Vref Timing specification test load voltage | Cref Timing specification capacitive load | Rref Timing specification resistance load | Cref_rising Timing specification capacitive load for | rising edges | Cref_falling Timing specification capacitive load for | falling edges | Rref_rising Timing specification resistance load for | rising edges | Rref_falling Timing specification resistance load for | falling edges | Vref_rising Timing specification test load voltage for | rising edges | Vref_falling Timing specification test load voltage for | falling edges | Vmeas_rising Measurement voltage for rising edge timing | measurements | Vmeas_falling Measurement voltage for falling edge timing | measurements | Rref_diff Timing specification differential | resistance load | Cref_diff Timing specification differential | capacitive load | | Usage Rules: [Model Spec] must follow all other subparameters under the | [Model] keyword. | | For each subparameter contained in the first column, the | remaining three hold its typical, minimum and maximum values. | The entries of typical, minimum and maximum must be placed on | a single line and must be separated by at least one white | space. All four columns are required under the [Model Spec] | keyword. However, data is required only in the typical | column. If minimum and/or maximum values are not available, | the reserved word "NA" must be used indicating the typical | value by default. | | The minimum and maximum values are used for specifications | subparameter values that may track the min and max operation | conditions of the [Model]. Usually it is related to the | Voltage Range settings. | | Unless noted below, no subparameter requires having present | any other subparameter. | | Vinh, Vinl rules: | | The threshold subparameter lines provide additional min and | max column values, if needed. The typ column values are still | required and would be expected to override the Vinh and Vinl | subparameter values specified elsewhere. Note: the syntax | rule that require inserting Vinh and Vinl under models remains | unchanged even if the values are defined under the [Model | Spec] keyword. | | Vinh+, Vinh-, Vinl+, Vinl- rules: | | The four hysteresis subparameters (used for Schmitt trigger | inputs for defining two thresholds for the rising edges and | two thresholds for falling edges) must all be defined before | independent input thresholds for rising and falling edges of | the hysteresis threshold rules become effective. Otherwise | the standard threshold subparameters remain in effect. The | hysteresis thresholds shall be at the Vinh+ and Vinh- values | for a low-to-high transition, and at the Vinl+ and Vinl- | values for a high-to-low transition. | | | | | Receiver Voltage with Hysteresis Thresholds | | | | | | Rising Edge Falling Edge | | Switching Region oo o Switching Region | | | o oo ooooooooo | | | V o o | | Vinh+ - - - - - - - - - - x o | | Vinh- - - - - - - - - - x o | | | o o | | | o o | | | o oV | Vinl+ - - - - - - - o - - - - - - - - - - - - - - - - - x | Vinl- - - - - - - - o - - - - - - - - - - - - - - - - - x | | o o | | o o | |oooooo-----------------------------------------------------oooooooo | | Time --> | | S_overshoot_high, S_overshoot_low rules: | | The static overshoot subparameters provide the DC voltage | values for which the model is no longer guaranteed to function | correctly. Typically these are voltages that would cause the | physical component to be destroyed. | | D_overshoot_high, D_overshoot_low, D_overshoot_time rules: | | The dynamic overshoot values provide a time window during | which the overshoot may exceed the static overshoot limits | but be below the dynamic overshoot limits. D_overshoot_time | is required for dynamic overshoot testing. In addition, if | D_overshoot_high is specified, then S_overshoot_high is | necessary for testing beyond the static limit. Similarly, if | D_overshoot_low is specified, then S_overshoot_low is | necessary for testing beyond the static limit. | | | | | Receiver Voltage with Static and Dynamic Overshoot Limits | | | | | | D_overshoot_time ->| |<- | | | | | D_overshoot_high - - - - - - -+ - - -+ | | | oo | Passes - Does Not Exceed Bounds | | |o o | | S_overshoot_high - - - - - - -x o +- - - - - - - - - - - - - - - - - - - | | o o ooooooooo | | o o o | | o o | | o o | | o o | | o o | | o o | | o o Fails - | | o o Exceeds Bounds | | o o | | | | | o o V V V | |oooooo-------------------------------------------o---------o---oooo | S_overshoot_low - - - - - - - - - - - - - - - - - - - - - x +x x x - - | | |o x x | | | o o| | D_overshoot_low - - - - - - - - - - - - - - - - - - - - - + -x x-+ | | | x | | D_overshoot_time ->| |<- | | Time --> | |* D_overshoot_area_h, D_overshoot_area_l, D_overshoot_ampl_h, |* D_overshoot_ampl_l rules: |* |* The dynamic overshoot area values define a maximum V-s |* area that an overshooting signal must not exceed. The high |* area is calculated from the point that a signal overshoots |* above the voltage defined by the [Power Clamp Reference] |* keyword until the point that the signal crosses back through |* this same voltage. If [Power Clamp Reference] is not |* defined, then this crossing voltage is assumed to be defined |* by the [Voltage Range] keyword. The low area is calculated |* from the point that a signal overshoots below the voltage |* defined by the [GND Clamp Reference] keyword until the point |* that the signal crosses back through this same voltage. If |* [GND Clamp Reference] is not defined, then this crossing |* voltage is assumed to be 0.0V. If D_overshoot_area_h is |* specified, then D_overshoot_ampl_h must also be specified. |* D_overshoot_ampl_h provides a maximum amplitude allowed for |* the overshoot area and is measured as voltage above the |* [Power Clamp Reference] voltage. Similarly, if |* D_overshoot_area_l is specified, then D_overshoot_ampl_l must |* also be specified. D_overshoot_ampl_l is measured as voltage |* below the [GND Clamp Reference] voltage. Both amplitude |* parameters should be listed as absolute (non-negative) values. |* Also, if D_overshoot_area_h, D_overshoot_area_l, |* D_overshoot_ampl_h, and D_overshoot_ampl_l are specified, then |* other static and dynamic overshoot parameters are optional. | |* | |* | Receiver Voltage with Dynamic Area Overshoot Limits |* | |* | |* | |* | |* D_overshoot_ampl_h - - - - - - ++- - - - - - - - - - - - - - - - - - - - |* D_overshoot_area_h - - - - - ->/o \ Passes - Does Not Exceed Overshoot |* | /o o \ Area nor Amplitude |* [Power Clamp Reference] - - --o o - - - - - - - - - - - - - - - - - - - |* | o o oooooooooo |* | o o o |* | o o |* | o o |* | o o |* | o o |* | o o Fails - Exceeds |* | o o Overshoot Area |* | o o and Amplitude |* | o o | |* | o o V |* |oooooo-------------------------------------------o---------o---oooo |* [GND Clamp Reference] - - - - - - - - - - - - - - - - - - -o - o-o o - |* | \o / x \o / |* D_overshoot_area_l - - - - - - - - - - - - - - - - - - - ->\o / x \ / |* D_overshoot_ampl_l - - - - - - - - - - - - - - - - - - - - -+x x - - -++ |* | x |* |* Time --> | | Pulse_high, Pulse_low, Pulse_time rules: | | The pulse immunity values provide a time window during which | a rising pulse may exceed the nearest threshold value but | be below the pulse voltage value and still not cause the | input to switch. Pulse_time is required for pulse immunity | testing. A rising response is tested only if Pulse_high is | specified. Similarly, a falling response is tested only if | Pulse_low is specified. The rising response may exceed the | Vinl value, but remain below the Pulse_high value. | | Similarly, the falling response may drop below the Vinh value, | but remain above the Pulse_low value. In either case the | input is regarded as immune to switching if the responses | are within these extended windows. If the hysteresis | thresholds are defined, then the rising response shall use | Vinh- as the reference voltage, and the falling response shall | use Vinl+ as the reference voltage. | | | | | Receiver Voltage with Pulse Immunity Thresholds | | | | | | Switching No Switching | | | | | | | oo o | Switching | | | o oo ooooooooo | | | | | o o | | | | V o o V oooV | Vinh - - - - - - - - - - x - - - - - - - - - - - - - x o + -x | | Pulse_time ->| o |<- |ooo | o | Pulse_high - - - - - + o - + Pulse_low - + - - + o | | |o | Pulse_time ->| |<- o | Vinl - - - - - - - - x + - - - - - - - - - - - - - - - - - - x | | o o | | o o | | o o | |oooooo------------------------------------------------------------o | | Time --> | | Vmeas, Vref, Cref, Rref rules: | | The Vmeas, Vref, Cref and Rref values under the [Model Spec] | keyword override their respective values entered elsewhere. | Note that a Vmeas, Vref, Cref or Rref subparameters may not be | used if its edge specific version (*_rising or *_falling) is | used. | | Cref_rising, Cref_falling, Rref_rising, Rref_falling, | Vref_rising, Vref_falling, Vmeas_rising, Vmeas_falling rules: | | Use these subparameters when specifying separate timing test | loads and voltages for rising and falling edges. If one | 'rising' or 'falling' subparameter is used, then the | corresponding 'rising' or 'falling' subparameter must be | present. The values listed in these subparameters override | any corresponding Cref, Vref, Rref or Vmeas values entered | elsewhere. | | Rref_diff, Cref_diff rules: | | The Rref_diff and Creff_diff values under the [Model Spec] | keyword override their respective values entered elsewhere. | These subparameters are used only when the model is referenced | by the [Diff Pin] keyword. These follow the same rules as | the corresponding subparameters documented under the [Model] | keyword. See Section 6b for more discussion on true and | single-ended differential operation. |----------------------------------------------------------------------------- [Model Spec] | Subparameter typ min max | | Thresholds | Vinh 3.5 3.15 3.85 | 70% of Vcc Vinl 1.5 1.35 1.65 | 30% of Vcc | | Vinh 3.835 3.335 4.335 | Offset from Vcc | Vinl 3.525 3.025 4.025 | for PECL | | Hysteresis | Vinh+ 2.0 NA NA | Overrides the Vinh- 1.6 NA NA | thresholds Vinl+ 1.1 NA NA Vinl- 0.6 NA NA | All 4 are required | | Overshoot | S_overshoot_high 5.5 5.0 6.0 | Static overshoot S_overshoot_low -0.5 NA NA D_overshoot_high 6.0 5.5 6.5 | Dynamic overshoot D_overshoot_low -1.0 -1.0 -1.0 | requires | | D_overshoot_time D_overshoot_time 20n 20n 20n | & static overshoot | |* Overshoot defined by area in V-s (Values from DDR2 specification) |* D_overshoot_ampl_h 0.9 NA NA | Dynamic overshoot D_overshoot_ampl_l 0.9 NA NA | requires area D_overshoot_area_h 0.38n NA NA | and amplitude D_overshoot_area_l 0.38n NA NA | parameters |* | Pulse Immunity | Pulse_high 3V NA NA | Pulse immunity Pulse_low 0 NA NA | requires Pulse_time 3n NA NA | Pulse_time | | Timing Thresholds | Vmeas 3.68 3.18 4.68 | A 5 volt PECL | | example | | Timing test load voltage reference example | Vref 1.25 1.15 1.35 | An SSTL-2 example | | | Rising and falling timing test load example (values from PCI-X | specification) | Cref_falling 10p 10p 10p Cref_rising 10p 10p 10p Rref_rising 25 500 25 | typ value not specified Rref_falling 25 500 25 | typ value not specified Vref_rising 0 1.5 0 Vref_falling 3.3 1.5 3.6 Vmeas_rising 0.941 0.885 1.026 | vmeas = 0.285(vcc) Vmeas_falling 2.0295 1.845 2.214 | vmeas = 0.615(vcc) | | Differential timing test load for true or single-ended differential model | Rref_diff 100 90 110 Cref_diff 5pF NA NA | |***************************************************************************** |* END NEW TEXT |***************************************************************************** ****************************************************************************** ANALYSIS PATH/DATA THAT LED TO SPECIFICATION While creating DDR2 SDRAM IBIS models, it was found that the AC Overshoot/ Undershoot specification could not be checked accurately by simulation tools given the parameters available for defining overshoot and undershoot under the [Model Spec] keyword. The DDR2 specification defines overshoot and undershoot in terms of a V-ns area. It was determined that adding two parameters to [Model Spec] to describe this area would give EDA software the necessary information to check for violations of the specification. ****************************************************************************** ANY OTHER BACKGROUND INFORMATION: ******************************************************************************