[ibis-interconn] Figured it out [External Reference]

From: Walter Katz <wkatz@xxxxxxxxxx>
To: "IBIS-Interconnect" <ibis-interconn@xxxxxxxxxxxxx>
Date: Wed, 7 Jan 2015 13:17:09 -0500 (EST)

All,

 

[External Reference] is applied in IBIS 6.0 in three places. First, it can
be used as a terminal to an External Model. Second it is used in a drawing
in the composite current section, presumable only to be used when the
device under test is an External Model. Finally, it can be used to adjust
the threshold based on its value. The implication is that when used as a
Reference_supply it is a static value supplied by the [External Reference]
keyword. This is different than if this voltage is supplied by a pin of a
component, which because of various power supply variations can change in
time. Does this mean that the thresholds like Vinh_dc are threshold that
dynamically change from edge to edge based on variation in the External
Reference voltage supplied to the buffer (which is now supported in our
new package modeling), or should one use the static value as defined in
the [External Reference] keyword?

 

Walter

 

See page 44, section on [Receiver Thresholds]

 

Vth(min/max) = Vth* + [(Threshold_sensitivity) X (change in supply
voltage)]

where Vth* is either Vth, Vth_min or Vth_max as appropriate, and the
supply voltage is the one indicated by the Reference_supply subparameter.

Examples:

A basic 3.3 V single ended receiver using only the required subparameters:

[Receiver Thresholds]

Vth = 1.5V

Vinh_ac = +225mV

Vinh_dc = +100mV

Vinl_ac = -225mV

Vinl_dc = -100mV

Tslew_ac = 1.2ns

 

A single ended receiver using an external threshold reference.  In this
case the input threshold is the external reference voltage so
Threshold_sensitivity equals 1.

[Receiver Thresholds]

Vth = 1.0V

Threshold_sensitivity = 1

Reference_supply Ext_ref

Vinh_ac = +200mV

Vinh_dc = +100mV

Vinl_ac = -200mV

Vinl_dc = -100mV

Tslew_ac = 400ps

 

 

Page 43:

Threshold_sensitivity is a unit-less number that specifies how Vth varies
with respect to the supply voltage defined by the Reference_supply
subparameter. Threshold_sensitivity is defined as:

 



 

Threshold_sensitivity must be entered as a whole number or decimal, not as
a fraction.

Reference_supply indicates which supply voltage Vth tracks; i.e., it
indicates which supply voltage change causes a change in input threshold.
The legal arguments to this subparameter are as follows:

 

Reference_supply indicates which supply voltage Vth tracks; i.e., it
indicates which supply voltage change causes a change in input threshold.
The legal arguments to this subparameter are as follows:

Power_clamp_ref        The supply voltage defined by the [POWER Clamp
Reference] keyword

Gnd_clamp_ref           The supply voltage defined by the [GND Clamp
Reference] keyword

Pullup_ref                   The supply voltage defined by the [Pullup
reference] keyword

Pulldown_ref              The supply voltage defined by the [Pulldown
reference] keyword

Ext_ref                        The supply voltage defined by the [External
Reference] keyword

 

Page 72:



Figure 1- [External Reference] - (used only for non-driver modes)




 

 

 

Walter Katz

 <mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx

Phone 303.449-2308

Mobile 303.335-6156

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Follow-Ups:
- [ibis-interconn] Re: Figured it out [External Reference]
  - From: Bob Ross

[ibis-interconn] Figured it out [External Reference]

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