The enclosed BIRD98: Gate Modulation Effect (table format), is submitted on behalf of Arpad Muranyi of Intel Corp. It will be discussed at the June 3rd, 2005 IBIS Open Forum teleconference. Thanks, Syed -- Cisco Systems, Inc Acting Chair - EIA IBIS Forum ****************************************************************************** ****************************************************************************** BIRD ID#: 98 ISSUE TITLE: Gate Modulation Effect (table format) REQUESTER: Arpad Muranyi, Intel Corp. DATE SUBMITTED: May 20, 2005 DATE REVISED: DATE ACCEPTED BY IBIS OPEN FORUM: PENDING ****************************************************************************** ****************************************************************************** STATEMENT OF THE ISSUE: The I-V and V-T tables of IBIS models are extracted at fixed, ideal supply voltage conditions. However, due to SSO noise, the actual drive strength (and consequently the edge rate) may vary during transients depending on the instantaneous value of the supply voltage. This phenomena is usually called the "gate modulation effect", which is not described by IBIS models. To achieve more accurate switching waveforms, and power and ground supply currents it would be desirable to include these effects in IBIS models. ****************************************************************************** STATEMENT OF THE RESOLVED SPECIFICATIONS: A new keyword, [Ishort Variations] shall be added to the specifiation to provide a table of saturation currents measured with respect to supply voltage variations. The information contained in the [Ishort Variations] table(s) enables the simulators to calculate scaling coefficients which may be used to scale the I-V tables as the instanteneous supply voltage changes from the nominal power supply values at which the I-V tables of the [Model]s were obtained. |============================================================================= | Keyword: [Ishort Variations] | Required: No | Description: The data points under this keyword define the short circuit | current of the pulldown, pullup, ground clamp, and/or power | clamp structures of a buffer as a function of the power supply | voltage. Currents are considered positive when their | direction is into the component. | | Simulators can use this information to calculate scaling | coefficients to scale the I-V tables as the instanteneous | supply voltage changes from the nominal power supply values | during power and/or ground bounce, and/or SSO simulation | events. | | The voltage axis of the table contains the supply voltage | values at which the short circuit currents provided in the | second, third and fourth columns of the table are measured. | The voltage axis should be centered around the typ., min., | max. supply voltages used by the buffer. The range of the | voltage axis may span as far as the buffer's characteristics | require, usually not more than down to 0 V and up to 2*Vcc. | | The assumption is that I-V tables obtained at nominal supply | voltages can be scaled with coefficients to generate new I-V | tables representing the buffer's characteristics at other | supply voltages. This assumption may provide reasonably | accurate results while the supply voltage variations remain | within the saturation region of the I-V tables, but may be | less accurate at larger variations. Based on this | assumption, an effective I-V table representing the buffer at | an arbitrary instanteneous supply voltage Vinst can be | calculated from a [Model]'s I-V table obtained at a nominal | supply voltage Vnom as: | | IV_effective(Vinst) = k(Vinst) * IV_model(Vnom) | | where k(Vinst) is calculated as: | | k(Vinst) = Ishort(Vinst) / Ishort(Vnom) | | where k(Vinst) is the scaling coefficient (used internally | by the simulator's algorithms) which scales the I-V table at | each iteration of the simulation, Vinst is the actual, | instantaneous power supply voltage between the pullup and | pulldown reference nodes or between the power clamp and | pulldown reference nodes, or between the pullup reference | and ground clamp reference nodes of the buffer model at each | iteration of the simulation, and Vnom is the corresponding | nominal value of the power supply voltage at which the I-V | tables were generated for the [Model] ([Voltage Range], or | [Pullup Reference]-[Pulldown Reference] for the pullup and | pulldown I-V tables, [POWER Clamp Reference]-[Pulldown | Reference] for the power clamp I-V tables, and [Pullup | Reference]-[GND Clamp Reference] for the ground clamp | tables). | | For example, if the typical I-V table of a 5 volt device has | a 100 mA data point at 5 V, and the associated [Ishort | Variations] keyword has 100 mA at 5 V and 90 mA at 4.5 V, | then the effective I-V table will be scaled down by 10 % at | an instance during a simulation when the instantenous supply | voltage of the model happens to be 4.5 V. | | Usage Rules: If used, the [Ishort Variations] keyword must immediately | follow the data tables after the [Pulldown], [Pullup], [GND | Clamp], and/or [Power Clamp] keywords. This is to guarantee | that the content of the [Ishort Variations] keyword and the | preceeding I-V table can be associated with each other. | | The first column contains the voltage value at which the | currents of the remaining three columns are obtained. The | three remaining columns contain the typical, minimum, and | maximum short circuit output current values. The short | circuit current of the pulldown and ground clamp tables are | obtained with the output pad shorted to the pullup reference | node, and the short circuit current of the pullup and power | clamp tables are obtained with the output pad shorted to the | pulldown reference node. | | The short circuit currents associated with the pullup and | pulldown I-V tables must be difference currents, i.e. the | corresponding short circuit current of a 3-stated buffer | must be first subtracted. | | All four columns are required under this keyword. However, | data is only required in the typical column. If minimum | and/or maximum current values are not available, the reserved | word "NA" must be used. "NA" can be used for currents in the | typical column, but numeric values MUST be specified for the | first and last voltage points in any table. Each table must | have at least 2, but not more than 100, rows. However, | these tables will be typically short, containing about 10-20 | points. | | The voltage values of these tables must be centered around | the the typical supply voltage of the [Model], and the short | circuit currents at the values of the typ., min., and max. | supply voltages must be the same as the current obtained | from the corresponding I-V tables at the same voltage. | | If the [Ishort Variations] keyword is not present, the power | supply variations will not have an effect on the I-V tables. | | The 1st (typical) column of the [Ishort Variations] keyword | is associated with the 1st (typical) column of the | corresponding I-V table, the 2nd (minimum) column is | associated with the 2nd (minimum) column of the | corresponding I-V table, and the 3rd (maximum) column is | associated with the 3rd (maximum) column of the | corresponding I-V table. | |----------------------------------------------------------------------------- [Ishort Variations] | | Voltage I(typ) I(min) I(max) | 0.0V 0.0m 0.0m 0.0m | . | . 4.0V 36.0m 29.0m 41.0m 4.5V 38.0m 30.0m 44.0m | Ishort_min must match I(4.5) min 5.0V 40.0m 31.0m 47.0m | Ishort_typ must match I(5.0) typ 5.5V 42.0m 32.0m 50.0m | Ishort_max must match I(5.0) max 6.0V 44.0m 33.0m 53.0m | in the corresponding I-V table | . | . 10.0V 50.0m 40.0m 60.0m | |============================================================================= ****************************************************************************** ANALYSIS PATH/DATA THAT LED TO SPECIFICATION This proposal is based on I-V curve data obtained from actual lab and simulation measurements. In the context of BIRD95, which attempts to refine the power and ground bounce simulation capabilities of IBIS simulators, this feature becomes very important, because the non-ideal ground and power supplies introduce significant deviations in the buffer's I-V curves, i.e. drive strength. Omitting these I-V curve variations reduces the accuracy of the SSO and power delivery simulations when the buffers are surrounded by non ideal power networks. ***************************************************************************** ANY OTHER BACKGROUND INFORMATION: This BIRD is a variant of BIRD 97. It is based on feedback received from Donald Telian, who suggested that this feature should be implemented using a table format instead of the equation proposed in BIRD 97. The advantages and disadvantages of the table and equation format are too numerous to list here. Since the table format seems to be much easier from the perspective of the model maker, this BIRD was written to replace BIRD 97 by a "NO" vote. Additional credits are due to Katja Koller and Bob Ross who were instrumental in writing and commenting on BIRD 97. ****************************************************************************** |------------------------------------------------------------------ |For help or to subscribe/unsubscribe, email majordomo@eda.org |with just the appropriate command message(s) in the body: | | help | subscribe ibis <optional e-mail address, if different> | subscribe ibis-users <optional e-mail address, if different> | unsubscribe ibis <optional e-mail address, if different> | unsubscribe ibis-users <optional e-mail address, if different> | |or email a written request to ibis-request@eda.org. | |IBIS reflector archives exist under: | | http://www.eda.org/pub/ibis/email_archive/ Recent | http://www.eda.org/pub/ibis/users_archive/ Recent | http://www.eda.org/pub/ibis/email/ E-mail since 1993Received on Fri May 20 17:15:54 2005
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