All,
This was discussed several months ago, now that we have a handle on GND
and Node 0, I think we should make the change suggested below.
Walter
On page 53, under:
Keywords: [Pulldown], [Pullup], [GND Clamp], [POWER Clamp]
It says:
Other Notes: The I-V table of the [Pullup] and the [POWER Clamp]
structures are "Vcc relative", meaning that the voltage values are
referenced to the Vcc pin. (Note that, under these keywords, all
references to "Vcc" refer to the voltage rail defined by the [Voltage
Range], [Pullup Reference], or [POWER Clamp Reference] keywords, as
appropriate.) The voltages in the data tables are derived from the
equation:
Vtable = Vcc - Voutput
Therefore, for a 5 V model, -5 V in the table actually means 5 V above
Vcc, which is +10 V with respect to ground; and 10 V means 10 V below Vcc,
which is -5 V with respect to ground. Vcc-relative data is necessary to
model a pullup structure properly, since the output current of a pullup
structure depends on the voltage between the output and Vcc pins and not
the voltage between the output and ground pins. Note that the [GND Clamp]
I-V table can include quiescent input currents, or the currents of a
3-stated output, if so desired.
When tabulating data for ECL models, the data in the [Pulldown] table is
measured with the output in the "logic low" state. In other words, the
data in the table represents the I-V characteristics of the output when
the output is at the most negative of its two logic levels. Likewise, the
data in the [Pullup] table is measured with the output in the "logic one"
state and represents the I-V characteristics when the output is at the
most positive logic level. Note that in BOTH of these cases, the data is
referenced to the Vcc supply voltage, using the equation:
Vtable = Vcc - Voutput
I think that a more correct statement would be:
Other Notes: The I-V table of the [Pullup] structures is "Pullup_ref
relative", meaning that the voltage values are referenced to the
Pullup_ref pin. (Note that, under these keywords, all references to
"Pullup_ref" refer to the voltage rail defined by the [Voltage Range], or
[Pullup Reference] keywords, as appropriate.) The voltages in the data
tables are derived from the equation:
Vtable = Pullup_ref - Voutput
The I-V table of the [POWER Clamp] structures is "Power_clamp_ref
relative", meaning that the voltage values are referenced to the
Power_clamp_ref pin. (Note that, under these keywords, all references to
"Power_clamp_ref" refer to the voltage rail defined by the [Voltage
Range], or [POWER Clamp Reference] keywords, as appropriate.) The voltages
in the data tables are derived from the equation:
Vtable = Power_clamp_ref - Voutput
The I-V table of the [Pulldown] structures is "Pulldown_ref relative",
meaning that the voltage values are referenced to the Pulldown_ref pin.
(Note that, under these keywords, all references to "Pulldown_ref" refer
to the voltage rail defined by the [Pulldown Reference] keyword.) The
voltages in the data tables are derived from the equation:
Vtable = Voutput- Pulldown_ref
The I-V table of the [GND Clamp] structures is "Gnd_clamp_ref relative",
meaning that the voltage values are referenced to the Gnd_clamp_ref pin.
(Note that, under these keywords, all references to "Gnd_clamp_ref" refer
to the voltage rail defined by the [GND Clamp Reference] keyword.) The
voltages in the data tables are derived from the equation:
Vtable = Voutput- Gnd_clamp_ref
Therefore, for a 5 V model (Vcc=[Voltage Range]=[Pullup Reference]=[POWER
Clamp Reference]=5.0V, [Pulldown Reference]=[GND Clamp Reference]=0.0V),
-5 V in the table actually means 5 V above Vcc, which is +10 V with
respect to ground; and 10 V means 10 V below Vcc, which is -5 V with
respect to ground. Vcc-relative data is necessary to model a pullup
structure properly, since the output current of a pullup structure depends
on the voltage between the output and Vcc pins and not the voltage between
the output and ground pins. Note that the [GND Clamp] I-V table can
include quiescent input currents, or the currents of a 3-stated output, if
so desired.
When tabulating data for ECL models, the data in the [Pulldown] table is
measured with the output in the "logic low" state. In other words, the
data in the table represents the I-V characteristics of the output when
the output is at the most negative of its two logic levels. Likewise, the
data in the [Pullup] table is measured with the output in the "logic one"
state and represents the I-V characteristics when the output is at the
most positive logic level. Note that in BOTH of these cases, the data is
referenced to the Vcc supply voltage, using the equation:
Vtable = Vcc - Voutput
Walter
Walter Katz
<mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 303.335-6156
