[ibis-macro] Draft BIRD for ATM teleconference
- From: <rrwolff@xxxxxxxxxx>
- To: <ibis-macro@xxxxxxxxxxxxx>
- Date: Tue, 4 Dec 2007 12:38:50 -0700
All,
Attached is a draft BIRD to discuss during today's teleconference. This
BIRD so far only covers the addition of a keyword for the DDR3 tVAC
parameter. I plan to add the slew rate derating at a later point.
Thanks,
Randy
Randy Wolff
SI Modeling Manager
Signal Integrity R&D Group
Micron Technology, Inc.
208-363-1764
<<bird_tvac.txt>>
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BIRD ID#: ???
ISSUE TITLE: DDR3 tVAC Parameter Support
REQUESTER: Randy Wolff, Micron Technology, Inc.
DATE SUBMITTED: ??
DATE ACCEPTED BY IBIS OPEN FORUM: PENDING
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STATEMENT OF THE ISSUE:
The JEDEC DDR3 SDRAM Specification (JESD79-3A) defines the tVAC parameter as
the
time that an input signal must remain above Vinh_ac or below Vil_ac for a valid
switching transition to occur. This parameter is needed (along with other
[Receiver Thresholds] parameters) to qualify a valid switching event.
This BIRD proposes adding a new keyword ([T_vac]) to the IBIS specification
that will give EDA software the data necessary to check for compliance with
the tVAC requirement.
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STATEMENT OF THE RESOLVED SPECIFICATIONS:
The following will be added after the [Receiver Thresholds] section in the
specification:
|=============================================================================
| Keyword: [T_vac]
| Required: No
| Description: The [T_vac] keyword relates to the DDR3 specification and
| defines the time that an input signal must remain above
| Vinh_ac or below Vil_ac for a valid switching transition to
| occur.
|
| Usage Rules: [T_vac] must only be present if the [Receiver Thresholds]
| keyword is present and should follow the [Receiver Thresholds]
| keyword.
|
| The first column contains the slew rate in V/ns. The slew rate
| is measured as defined by the DDR3 specification. The nominal
| rising edge slew rate is defined as the slew rate between the
| last crossing of Vth and the first crossing of Vih_ac. The
| nominal slew rate for a falling edge is defined as the slew
| rate between the last crossing of Vth and the first crossing
| of Vil_ac. If the actual signal is always earlier than the
| nominal slew rate line between the Vth and Vih_ac or Vil_ac
| points, then the nominal slew rate is compared to the slew
| rate defined under the [T_vac] keyword. If the actual signal
| is later than the nominal slew rate line anywhere between the
| Vth and Vih_ac or Vil_ac points, the slew rate of a tangent
| line to the actual signal from the signal to Vih_ac or Vil_ac
| is compared to the slew rate defined under the [T_vac] keyword.
| More information about measuring this slew rate can be found in
| the JEDEC DDR3 specification.
|
| The second column contains the tVAC value in ps. This value
| is the minimum required time above vih_ac or below vil_ac for
| a valid transition.
|
| The two entries, slew rate and tVAC, must be placed on a single
| line and must be separated by at least one white space.
|
| For slew rates in between the values listed under the [T_vac]
| keyword, tVAC values can be obtained by linear interpolation.
| For slew rates greater than the largest value listed, it is
| assumed that the tVAC value associated with the largest slew
| rate applies. For slew rates less than the smallest value
| listed, it is assumed that the tVAC value associated with the
| smallest slew rate applies.
|
|-----------------------------------------------------------------------------
[T_vac]
| Slew rate(V/ns) tVAC(ps)
|
2.01 75
2.0 57
1.5 50
1.0 38
0.9 34
0.8 29
0.7 22
0.6 13
0.5 0
0.49 0
|
|=============================================================================
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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION
With the addition of the tVAC parameter to the JEDEC DDR3 specification, it is
necessary to add this parameter to the IBIS specification. In order for EDA
software to properly qualify a signal at the input to a DDR3 receiver, the
software needs information about the tVAC parameter. With this additional
information, the software can determine the slew rate of the signal, compare
that to the table of values supplied under the [T_vac] keyword, and then
determine if the signal remained above Vinh_ac or below Vil_ac for a long
enough period of time to qualify as a valid transition.
For more information on the DDR3 tVAC specification, refer to the JEDEC
document JESD79-3A available at the following url:
http://www.jedec.org/download/search/JESD79-3a.pdf
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ANY OTHER BACKGROUND INFORMATION:
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