Mike,
Thanks for correcting me on that, and apologies for not remembering the
exact words in the spec (or not taking the time to look it up in this
discussion before writing a reply).
Looks like you are right, and the spec is correct in the sense that the
[Voltage Range] keyword is described as a keyword that defines a "voltage
rail" to which the [Pullup] and [POWER Clamp] I-V data is referenced. But what
is
the significance of the word "default" in that sentence? What can be a
reason to deviate from this default?
But I think I was also right with my comment because it says "Defines the
power supply voltage". The big question here is that if one point of that
voltage is this "voltage rail" to which the [Pullup] and [POWER Clamp] I-V
data is referenced, what is the other point of that voltage reading? In
my mind it is the "voltage rail" to which the [Pulldown] and [GND Clamp]
I-V data is referenced, but if I remember correctly that is not stated in the
spec, and consequently the question is, did we assume that this other
unnamed rail is node 0 itself, or did we assume that it can it be
connected to any DC voltage the user pleases to use?
In my mind it was the latter, and for that reason I think of [Voltage
Range] as a voltage definition for a voltage that is between the power
and ground rails on the die, and NOT as a voltage that is between the
power rail on the die and node 0. After all, shorting the ground rail
on the die to node 0 would kill the ground pin package parasitics,
because they would be shorted to node 0. Also, if we assumed that the
voltage in [Voltage Range] is between the power rail and node 0, we
have an undefined, dangling rail for the bottom side of the buffer.
So what is the reference of the voltage in the [Voltage Range] keyword?
Thanks,
Arpad
========================================================================
From: ibis-editorial-bounce@xxxxxxxxxxxxx
[mailto:ibis-editorial-bounce@xxxxxxxxxxxxx] On Behalf Of Mirmak, Michael
Sent: Thursday, April 21, 2016 9:41 PM
To: wkatz@xxxxxxxxxx; Muranyi, Arpad <Arpad_Muranyi@xxxxxxxxxx>;
ibis-editorial@xxxxxxxxxxxxx
Subject: [ibis-editorial] Re: Draft DUT and reference language for specification
Actually, [Voltage Range] *does* define a rail. From the specification
(emphasis added):
Keyword: [Voltage Range]
Required: Yes, if [Pullup Reference], [Pulldown Reference], [POWER Clamp
Reference], and [GND Clamp Reference] are not present
Description: Defines the power supply voltage tolerance over which the model is
intended to operate. It also specifies the default voltage rail to which the
[Pullup] and [POWER Clamp] I-V data is referenced
In other words, [Voltage Range] actually, and refreshingly, defines the
reference rail for [Pullup] and [POWER Clamp].
- MM
From:
ibis-editorial-bounce@xxxxxxxxxxxxx<mailto:ibis-editorial-bounce@xxxxxxxxxxxxx>
[mailto:ibis-editorial-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Thursday, April 21, 2016 6:32 PM
To: Muranyi, Arpad; Mirmak, Michael;
ibis-editorial@xxxxxxxxxxxxx<mailto:ibis-editorial@xxxxxxxxxxxxx>
Subject: [ibis-editorial] Re: Draft DUT and reference language for specification
Arpad,
[Voltage Range] can, in fact can be 0.0V. Look at the ECL_0V model in the
enclosed IBIS file that Bob supplied.
In this case:
[Voltage Range] 0.0V 0.0V 0.0V
[GND Clamp Reference] -5.0V -5.0V -5.0V
Is equivalent to the following
[Pullup Reference] 0.0V 0.0V 0.0V
[Pulldown Reference] 0.0V 0.0V 0.0V
[POWER Clamp Reference] 0.0V 0.0V 0.0V
[GND Clamp Reference] 0.0V 0.0V 0.0V
In this case there are 3 terminals that connect to 0.0V, but [Pin Mapping]
tells us that they all connect to signal_name VEE, which is also Model_name
GND. The Test Fixture reference node connects to this VEE pin, and therefore
the VEE connection to the buffer is the reference node.
Your statement:
Also, this doesn't seem to define what the reference node is for the buffer
terminals whose voltage value is defined by the four *** Reference keywords.
Is only true if all of the *** Reference keywords are not 0.0V.
I agree that IBIS does not explicitly say this is what you should do, but it
seems like a very logical assumpltion when one of the *** Reference keywords is
0.0V.
Walter
From: Muranyi, Arpad [mailto:Arpad_Muranyi@xxxxxxxxxx]
Sent: Thursday, April 21, 2016 9:09 PM
To: wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>;
michael.mirmak@xxxxxxxxx<mailto:michael.mirmak@xxxxxxxxx>;
ibis-editorial@xxxxxxxxxxxxx<mailto:ibis-editorial@xxxxxxxxxxxxx>
Subject: RE: Draft DUT and reference language for specification
Walter,
This doesn't make sense: "...are referenced to a rail whose value of [Voltage
Range],
[Pullup Reference], [Pulldown Reference], [POWER Clamp Reference], or [GND
Clamp Reference] is 0.0V".
Voltage Range is not referring to a "rail", it specifies a voltage difference
between two rails. If I remember correctly, the spec doesn't state what those
two rails are.
Also, this doesn't seem to define what the reference node is for the buffer
terminals whose voltage value is defined by the four *** Reference keywords.
I think what we want to achieve is a definition that tells us what the
"other node" is for the voltages associated with these four keywords and
their corresponding buffer terminals:
[Pullup Reference], [Pulldown Reference], [POWER Clamp Reference], or [GND
Clamp Reference]
Thanks,
Arpad
===============================================================================
From:
ibis-editorial-bounce@xxxxxxxxxxxxx<mailto:ibis-editorial-bounce@xxxxxxxxxxxxx>
[mailto:ibis-editorial-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Thursday, April 21, 2016 6:56 PM
To: michael.mirmak@xxxxxxxxx<mailto:michael.mirmak@xxxxxxxxx>;
ibis-editorial@xxxxxxxxxxxxx<mailto:ibis-editorial@xxxxxxxxxxxxx>
Subject: [ibis-editorial] Re: Draft DUT and reference language for specification
MM,
The [Receiver Thresholds] section does do DIA by allowing Vinl_dc, Vinh_dc,
Vinl_ac and Vinh_ac to be adjusted by the rail voltage supplied to one of the
rails, but it is not clear what the voltage supplied to the rail is referenced
to. This was the presentation on made to IBIS-ATM on Tuesday (enclosed).
One might want to add the following:
Although not specifically stated in IBIS, EDA vendors generally assume that the
reference for all DUT keyword and subparameter voltage values, as well as
[Model] subparameters such as C_comp, Vinh, Vinl, and Vmeas are referenced to a
rail whose value of [Voltage Range], [Pullup Reference], [Pulldown Reference],
[POWER Clamp Reference], or [GND Clamp Reference] is 0.0V.
I personally would add this to the standard. If, for example, [GND Clamp
Reference] is 0.0V, then it is logical that this is also the reference for the
DUT test fixture. To me the problem is when [Voltage Range], [Pullup
Reference], [Pulldown Reference], [POWER Clamp Reference], and [GND Clamp
Reference] are all non zero.
Walter
From:
ibis-editorial-bounce@xxxxxxxxxxxxx<mailto:ibis-editorial-bounce@xxxxxxxxxxxxx>
[mailto:ibis-editorial-bounce@xxxxxxxxxxxxx] On Behalf Of Mirmak, Michael
Sent: Thursday, April 21, 2016 4:50 PM
To: ibis-editorial@xxxxxxxxxxxxx<mailto:ibis-editorial@xxxxxxxxxxxxx>
Subject: [ibis-editorial] Draft DUT and reference language for specification
Please find enclosed proposed language for the IBIS document to address the
distinction between DUT and DIA. Note that the list of keywords will need
careful scrutiny and is likely not complete here.
These paragraphs should appear in Chapter 2 or Chapter 6. Some editing of
Chapter 2's language, particularly the use of the word "model", is needed
regardless of where the new text is added.
Comments are certainly welcome and encouraged.
- MM
-----------------------------------------------------
"IBIS files do not define buffer "models". Instead, keywords and subparameters
in IBIS files describe device behaviors in terms of data sets, to be used in
combination with model equations and assumptions defined within EDA simulation
tools. These data sets are generally assumed to have been collected under
static conditions using a test fixture. In other words, IBIS buffer data
generally describes a "device under test" (DUT), where the actual modeling of
the collected data is performed by the EDA simulator.
Not all the DUT fixture conditions are currently defined in IBIS. In
particular, the node used as a reference for the rails defined by, and voltage
value arguments for, the [Voltage Range], [Pullup Reference], [Pulldown
Reference], [POWER Clamp Reference], and [GND Clamp Reference] keywords is not
specified. Similarly, the node to be used as a reference for the voltage
arguments to the [Receiver Thresholds] keyword subparameters, and the [Model]
keyword Vinh and Vinl subparameters, is not explicitly stated. While the
C_comp_pullup, C_comp_pulldown, C_comp_power_clamp, and C_comp_ground_clamp
subparameters define references for I/O capacitances, the reference for the
C_comp subparameter is also not specifically defined. The specification
generally assumes that the same single node, separate from the I/O pad, buffer
supply rail, or any package pin, is used as the reference for all DUT keyword
and subparameter voltage values, as well as [Model] subparameters such as
C_comp, Vinh, Vinl, and Vmeas. Specific EDA vendors, however, may make
different assumptions or permit user assignment of the reference to another
defined point (e.g., a specific pin).
The behavior of most IBIS data in EDA tool models under conditions other than
those use to extract that data - called "device in action" (DIA) - is not
currently defined by the specification and may vary between simulators.
Exceptions to this include the [ISSO_PU], [ISSO_PD], and [Composite Current]
keywords, where data and data-collection conditions are provided for both DUT
and DIA contexts."
- MM
