Subject: Bird63.3 -- Documentation of receiver setup and hold conditions

From: "Peters, Stephen" <[email-masked]>
Date: Tue, 22 Feb 2000 09:28:33 -0800

Hello All:

  In response to Bob's comments here is an updated Bird 63.  
In brief, major changes include renaming the Tester_slew_rate parameter
to Edge_rate, and specifying edge rate over the 20% to 80% voltage swing.
In addition, for differential receivers the Vth_tester parameter
now represents the cross point of the two differential signals and
does not have to be set to any specific voltage.  Both the bird (BIRD 63)
and BIRD 62 will be up for discussion at this Friday's meeting.

   Regards,
   Stephen Peters
   Intel Corp.

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                Buffer Issue Resolution Document  (BIRD)

BIRD ID#:     63.3
ISSUE TITLE:  Documentation of Receiver Setup and Hold Timing Conditions
REQUESTOR:    D.C. Sessions (Philips), Stephen Peters, Richard Mellitz,
              Arpad Muranyi (Intel Corp.)
DATE SUBMITTED:  Sept 8, 1999, Dec 27, 1999, Jan 6, 2000, Feb 17, 2000
DATE ACCEPTED BY IBIS OPEN FORUM:

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STATEMENT OF THE ISSUE:  Currently, the edge rate and overdrive conditions
under which a receiver's data book setup and hold timings are specified are
not documented.  This bird provides a way for the model creator to document
those conditions in an IBIS file.

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STATEMENT OF THE RESOLVED SPECIFICATIONS:

1) The following new keyword is defined and placed in the specification
just below the [Receiver Threshold] keyword.

|===========================================================================
=
|      Keyword: [Tester Spec]
|     Required: No
|   Sub-Params: Vlow_tester, Vhigh_tester, Vth_tester, Edge_rate_setup, 
|               Edge_rate_hold
|  Description: The [Tester Spec] keyword documents the input overdrive
|               and waveform edge rate conditions under which a device's
|               input setup and hold times are specified.  The subparameters
|               are defined as follows:
|
|               Vth_tester is the point on the input waveform from which
|               a receivers' setup and hold time is referenced.  It is
|               usually the input voltage at which the output of a digital
|               logic receiver changes state.  Vth_tester is used as the
|               reference voltage for the Vlow_tester and Vhigh_tester
|               parameters. For a differential receiver Vth_tester
represents
|               the voltage point at which the true and complement input 
|               waveforms cross.
|
|               Vlow_tester represents the starting voltage of the
low-to-high
|               going waveform a tester uses when characterizing a
receiver's
|               setup or hold time. It also represents the ending voltage of
a
|               high-to-low going waveform.  Vlow_tester is expressed as an
|               offset from Vth_tester.
|
|               Vhigh_tester represents the ending voltage of the
low-to-high
|               going waveform a tester uses when characterizing a
receiver's
|               setup or hold time. It also represents the starting voltage
of
|               a high-to-low going waveform.  Vhigh_tester is expressed as
an
|               offset from Vth_teseter.
|
|               Edge_rate_setup is the slope of the input waveform used when
|               specifying a receivers setup time.  The slope must be valid
|               over the 20% to 80% points of the input voltage swing and is

|               calculated as follows:
|
|
|                           (Vhigh_tester - Vlow_tester) X 0.6
|     Edge_rate_*      = ------------------------------------------
|                         time it takes to swing the above voltage
|
|               Edge_rate_hold is the slope of the input waveform used when
|               specifying a receivers hold time.  The slope must be valid 
|               over the 20% to 80% points of the input voltage swing and is

|               calculated as shown above:
| 
|               Both Edge_rate_setup and Edge_rate_hold must be entered as 
|               an unreduced fraction, with the numerator representing the
|               actual deltaV and the denominator representing the actual 
|               deltaT.
|
| Usage Rules:  The [Tester Spec] keyword is valid if the model type
|               includes any reference to input or I/O.  All subparameters
|               are required to be present.  When entering a numeric value
the
|               subparameter argument and the subparameter itself must be
|               separated by an equals sign (=).  The argument to the
|               Edge_rate_* parameters are separated from the parameter
itself
|               by white space.
|
|               Differential Receivers:
|               For a differential receiver the input setup and hold times
|               are specified with respect to the crossing point of the two
|               input waveforms as one switches L->H and the other switches
|               H->L. Therefore, if the [Tester Spec] keyword is describing 
|               a differential receiver (i.e. is part of a [Model] statement

|               that describes a pin listed in the [Diff Pin] keyword), then

|               the numerical value of Vth_tester is assumed to be the point
|               at which the two input waveforms (the "true" and
"complement"
|               inputs) cross.  As with a single ended receiver, the true
and
|               complement inputs are assumed to switch between Vlow_tester 
|               and Vhigh_tester.
|
|
| A basic 3.3v single ended receiver
Vth_tester   = 1.5v
Vlow_tester  = -1.0v
Vhigh_tester = 1.0v
Edge_rate_setup 1.2v/1.2nS
Edge_rate_hold  1.2v/1.2nS
|
| A 2.5V SSTL receiver
Vth_tester   =  1.25v
Vlow_tester  = -0.75v
Vhigh_tester =  0.75v
Edge_rate_setup 900mv/0.9nS
Edge_rate_hold  900mv/0.9nS
|
| A differential receiver
Vth_tester   = 0.65v
Vlow_tester  = -500mV
Vhigh_tester = +500mV
Slew_rate_setup  600mV/0.36nS  
Slew_rate_hold   600mV/0.36nS
|
|
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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION:  Like it's companion BIRD #62,
this bird is an attempt to better specify and document a receiver's
functionality.  It follows the convention of the previous BIRDS in that
most of the parameter values are specified as an offset from a reference
voltage.  This technique supports both single ended and differential
receivers.

Note that there are separate slew rate entries for setup and hold time.
When
formulating this bird the authors were not sure if receiver hold time was
specified under different slew rate conditions than setup time.  Thus,
separate slew rate entries.  These two parameters can be collapsed into one
if further information indicates that this is not the case.

Updates for 63.1:
  Corrected "Tester_Skew" to "Tester_Slew" in the examples (typo
correction) and fixed up the Slew_rate equation by removing the
absolute value markers.  Changed Slew_rate so that it is expressed
as an explicit ratio and not as a decimal (following the convention of
[Ramp Rate]).  Clarified the meaning of Tester_Vth.  Finally, under 
"Differential Receivers:" changed the text to indicate that the numerical 
value of Tester_Vth is *typically* given as 0v rather than *must* be given 
as zero. 

Updates for 63.2:
  Syntax correction -- the argument to the Tester_Slew_* parameter should
be separated from the subparameter by white space, not an equals sign 
(it's a non-numeric argument).  Corrected examples.

Updates for 63.3
  Tester_slew_rate (parameter and definition) was replaced by the
Edge_rate_* parameter, where edge rate is specified from the 20%
to 80% points on the input waveform.  Vth_tester for a differential 
receiver now represents the crossing point of the two input waveforms, 
which is where the input setup and hold timing for a differential receiver
are supposed to be referenced.  Subparameter names have been changed
to better conform to IBIS usage.

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ANY OTHER BACKGROUND INFORMATION: This BIRD is a direct result of a
request by the JEDEC JC-16 committee to the IBIS Open Forum to provide
better
specification of receivers.  The basic form of this bird was discussed at
a meeting in July 1999 between DC Sessions of Phillips Corp. and Stephen
Peters, Richard Mellitz and Aprad Muranyi of Intel Corp.

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