All,
I think there was some consensus among some of use that the best
approach to cleaning up differential measurement rules had two
independent paths. A third independent path is to generally clean up the
existing single ended and differential rules.
The ?first? path is to implement additional differential rules as
additional rules in the single ended active high pin of differential
pairs (as currently implemented). These new rules might include
derating, tVac, slew rate measurement options, Eye Template (aka Eye
Compliance, Eye Mask, Eye Aperture) rules, ?These enhancements to
differential rules, along with additional enhancements to Single Ended
rules can be implemented in months (if not weeks).
The ?second? is to agree that in a future IBIS release that we would
remove [Diff_pin] and replace it with [Diff_pin_model], and require that
all differential ?stuff? be in [Diff_Model] sections instead of [Model]
sections. I included the last e-mail containing an example of a
differential model done both using existing 4.2 and the proposed ?5.0?
method.
The ?third? is to agree to clean up existing single ended and
differential measurement rules. Candidate for this cleanup are:
Tdiffslew_ac and Tslew_ac should be defined as between DC and AC instead
of AC and AC
Add single ended derating
Add single ended tVac rules
Add single ended eye compliance rules
Deprecate the following single ended IBIS rules
Vinh+
Vinh-
Vinl+
Vinl-
Pulse_high
Pulse_low
Pulse_time
Deprecate the following
[Comment Char]
The content of the files is case sensitive, except for reserved words
and keywords.
Note the definition of Deprecate
To make invalid or obsolete by flagging the item. When commands or
statements in a language are planned for deletion in future releases of
the compiler or rendering engine, they are said to be deprecated.
I think the first step is to decide if and when we will take on the
?first?, ?second? and/or ?third? paths. Agree on the goals of each of
these paths (both general content and implementation schedule). Then
agree to an implementation plan.
I personally would recommend the following specific actions in our
January 8 meeting:
1. Agree to move forward on the ?first? and ?third? options above,
with a goal of submitting a formal Bird for approval by the end of
Q1/08.
2. Agree to ?Deprecate? [Diff_pin]. This is simply a statement to the
IBIS users that in some future IBIS (e.g. 5.0 in 2009) that a
different approach to differential will be implemented.
Walter
Brief outline of [Diff_model] concept (by example).
Existing implementation
-----------------------
[Component] MEM
[Manufacturer] SiSoft
[Pin] signal_name model_name R_pin L_pin C_pin
E8 DQS+ DQS 41.35m 1.55nH 0.13pF
F8 DQS- DQS 42.93m 1.55nH 0.12pF
[End Pin]
|
[Diff_pin] inv_pin vdiff tdelay_typ tdelay_min tdelay_max
E8 F8 .250V 0ns -50ps 50ps
[End Diff_pin]
|
[End Component]
|
[Model] DQS
Model_type I/O
? normal single pin IBIS stuff
[Receiver Thresholds]
Vcross_low = 0.675V
Vcross_high = 1.125V
Vdiff_ac = 500mV
Vdiff_dc = 250mV
Tdiffslew_ac = 5.000ns
[End Receiver Thresholds]
? normal single pin IBIS stuff
[End Model]
[End]
Proposed implementation
-----------------------
[Component] MEM
[Manufacturer] SiSoft
[Pin] signal_name model_name R_pin L_pin C_pin
E8 DQS+ DQS 41.35m 1.55nH 0.13pF
F8 DQS- DQS 42.93m 1.55nH 0.12pF
[End Pin]
|
[Diff_pin_model] inv_pin diff_model
E8 F8 DQS_DIFF
[End Diff_pin]
|
[End Component]
|
[Model] DQS
Model_type I/O
? normal single pin IBIS stuff (exclude differential [Receiver
Thresholds] stuff)
[End Model]
|
[Diff_model] DQS_DIFF
Model_type Pseudo_Differential_I/O
|
Single_ended_capable True
|
| Buffer model
|
| Model
Single_ended_model DQS
| or
Active_high_model DQS
Active_low_model DQS
| and? /or
[External Model]
?
[End External Model]
|
| Transmit active high/low skew
|
[Transmit Thresholds]
tdelay_typ = 0ns
tdelay_min = -50ps
tdelay_max = 50ps
| or
tdelay 0ns -50ps 50ps
[End Transmit Thresholds]
|
| Receiver analysis
|
[Algorithmic Model]
Executable Windows_VisualStudio_32 dqs.dll dqs.ami
[End Algorithmic Model]
|
[Receiver Thresholds]
Vcross_low = 0.675V | Minimum common mode voltage at differential
signal crossing 0V
Vcross_high = 1.125V | Maximum common mode voltage at differential
signal crossing 0V
Vdiff = 250mV
Vdiff_ac = 500mV
Vdiff_dc = 250mV
Tdiffslew_ac = 5.000ns
[End Receiver Thresholds]
|
|
[End Diff_model]
|
[End]
