---------------------------------------------------------------- Buffer Issue Resolution Document (BIRD) BIRD ID#: 3 ISSUE TITLE: Multiple power supplies and references REQUESTER: Stephen Peters, Intel Corp. DATE SUBMITTED: Nov 4, 1993 DATE ACCEPTED BY IBIS OPEN FORUM: November 12, 1993 ****************************************************************************** ****************************************************************************** STATEMENT OF THE ISSUE: The IBIS specification currently does not address devices that use more than one supply, or devices in which the pullups, pulldowns, power_clamp or gnd_clamp diodes are referenced to voltages other than that specified by the [Voltage range] keyword. This BIRD proposes a general way in which both multiple power supplies can be defined and V/I curve can be referenced to specific supplies. **************************************************************************** STATEMENT OF THE RESOLVED SPECIFICATIONS: The specific change involves adding four new keywords: [Pullup reference], [Pulldown reference], [POWER_clamp reference] and [GND_clamp reference]. These keywords are defined as shown below. The following text replaces the current text for the [Voltage range] keyword. |========================================================================== | Keyword: [Voltage range] | Required: Yes |Description: Used to define the power supply voltage tolerance over which | the the model is intended to operate. It also specifies the | default voltage rail the pullup and POWER_clamp V/I data is | referenced to. |Usage Rules: Actual voltages (not percentages) are to be presented in the | usual typ, min, max format. "NA" is allowed for the min and | max values only. |--------------------------------------------------------------------------- | variable typ min max [Voltage range] 5.0v 4.5v 5.5v |=========================================================================== | Keyword: [Pullup reference] | Required: Yes, if the [Voltage range] keyword is not present. |Description: Used to define a voltage rail other than that defined by | the [Voltage range] keyword as the reference voltage | for the pullup V/I data. |Usage Rules: Actual voltages (not percentages) are to be presented in the | usual typ, min, max format. "NA" is allowed for the min and | max values only. |Other Notes: This keyword, if present, also defines the voltage range over | which the min and max dV/dt_r values are derived. |--------------------------------------------------------------------------- | variable typ min max [Pullup reference] 5.0V 4.5V 5.5V |=========================================================================== | Keyword: [Pulldown reference] | Required: Yes, if the [Voltage range] keyword is not present. |Description: Used to define a power supply rail other than 0v as the | reference voltage for the pulldown V/I data. If this keyword | is not present the voltage data points in the pullup V/I table | are referenced to 0v. |Usage Rules: Actual voltages (not percentages) are to be presented in the | usual typ, min, max format. "NA" is allowed for the min and | max values only. |Other Notes: This keyword, if present, also defines the voltage range over | which the min and max dV/dt_f values are derived. |--------------------------------------------------------------------------- | variable typ min max [Pulldown reference] 0V 0V 0V |=========================================================================== | Keyword: [POWER_clamp reference] | Required: Yes, if the [Voltage range] keyword is not present. |Description: Used to define a voltage rail other than that defined by | the [Voltage range] keyword as the reference voltage | for the POWER_clamp V/I data. |Usage Rules: Actual voltages (not percentages) are to be presented in the | usual typ, min, max format. "NA" is allowed for the min and | max values only. |Other Notes: Refer the "NOTES ON SPECIFYING POWER SUPPLIES" section below. |--------------------------------------------------------------------------- | variable typ min max [POWER_clamp reference] 5.0V 4.5V 5.5V |=========================================================================== | Keyword: [GND_clamp reference] | Required: Yes, if the [Voltage range] keyword is not present. |Description: Used to define a power supply rail other than 0v as the | reference voltage for the GND_clamp V/I data. If this keyword | is not present the voltage data points in the pullup V/I table | are referenced to 0v. |Usage Rules: Actual voltages (not percentages) are to be presented in the | usual typ, min, max format. "NA" is allowed for the min and | max values only. |Other Notes: Refer to the "NOTES ON SPECIFYING POWER SUPPLIES" section below. |--------------------------------------------------------------------------- | variable typ min max [GND_clamp reference] 0V 0V 0V |============================================================================ | NOTES ON SPECIFYING POWER SUPPLIES | It is the intention that standard TTL and CMOS devices be specified | using only the [Voltage range] keyword. However, in cases where | the output characteristics of a device depend on more than a single | supply and ground, or a pullup, pulldown or clamp structure is referenced | to something other than the default supplys, the additional 'reference' | keywords are to be used. | If the [Voltage range] keyword is not present then all four of the | other keywords must be present. If the [Voltage range] keyword is | present the other keywords are optional and may or may not be used as | required. It is legal (although redundant) for an optional keyword to | specify the same voltage as specified by the [Voltage range] keyword. ******************************************************************************* ANALYSIS PATH/DATA THAT LED TO SPECIFICATION: Most of the above is fairly self-explanatory. The key here is to realize that the four 'reference' keywords, in effect, create separate power supply rails that override the default [Voltage range] supply. The intention was to create a very general and flexible way to handle multiple supply devices and ECL. To illustrate with some examples: 1. An RS23 line driver has a +/- 12V output swing. One way to specify this device is shown below typ min max [Voltage range] 12.0V 11.5V 12.5V | fixes pullup and | POWER_clamp ref [Pulldown reference] -12.0V -12.5V -11.5V | fixes pulldown ref [GND_clamp reference] -12.0V -12.5v -11.5V | fixes GND_clamp ref Optionally, the [Voltage range] keyword could be replaced with the [Pullup reference] and [POWER_clamp] reference. 2. A device uses two supplies, a 3V supply for its I/O and a 5V supply for it's internal logic. The power clamp diodes are referenced to the 5V supply. Their are two equally valid ways this device can be specified. typ min max [Voltage range] 3.3V 3.0V 3.6V | fixes pullup reference [POWER_clamp reference 5.0V 4.5V 5.5V | fixes POWER_clamp | reference typ min max [Voltage range] 5.0V 4.5V 5.5V | fixes both pullup and | POWER_clamp reference [Pullup reference] 3.3V 3.0V 3.6V | overrides [Voltage | range] specification | on the pullup 3. When specifying a device with an ECL type output structure, the pulldown curves must be referenced to the most positive supply (the same one that the pullup curves are referenced to). The easiest way to do this is define the value of the [Voltage range] as 0v. Both the pullup AND pulldown V/I curves will be referenced to 0v (remember, the pulldown defaults to 0v). typ min max [Voltage range] 0V 0V 0V | VCC supply [Pulldown reference] 0V 0V 0V | not really | required, its | specified for | completeness [GND_clamp reference] -4.5V -3.5V -5.5V | ESD diode Alternately, one could specify the VEE supply and then override the default values of the pullup and pulldown references typ min max [Voltage range] -4.5V -4.0V -5.5v | VEE supply [Pullup reference] 0v 0v 0V [Pulldown reference] 0v 0v 0v [GND_clamp reference] -4.5V -3.5V -5.5V | ESD diode Finally, to specify ECL logic that is used with a +5V supply (positive ECL) one can do the following: typ min max [Voltage range] 5.0V 4.5V 5.5V | VCC supply [Pulldown reference] 5.0V 4.5V 5.5V | override default The default references are used for the pullup and GND_clamp V/I curves. ****************************************************************************** ANY OTHER BACKGROUND INFORMATION: ******************************************************************************