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Fig. 6.
Simplified schematic of the driver circuit
(a)
I
pu
(b) Capacitance
Fig. 7.
Test-benches for extracting model elements: (a) pull-up current
I
pu
(a) output capacit-
ance
C
gnd
and
C
power
The data was used to fit rational function models in the form:
PX
()
fX
()
=
(2)
QX
()
where
P
and
Q
are polynomial functions in
X
={x
1
,x
2
,…,x
n
}and
Q
is non zero.
P
and
Q
have no common factor of positive degree.
Similarly, the pull-down current model
I
pd
was extracted by turning on the pull-
down network and turning off the pull-up network.
I
pd
was extracted as a model func-
tion of PVT variations and
V
pd
, where
V
pd
is defined as the voltage difference between
the output and the ground.
The test setup for extracting the output parasitic capacitance is shown in Fig. 7(b).
An AC signal is attached to the output ports and the imaginary currents in the power
and the ground ports are measured. The capacitances
C
power
and
C
gnd
were derived
using
−ℑ
(
I
)
ℑ
(
I
)
gnd
C
=
VCC
,
C
=
(3)
gnd
power
2
π
fV
2
π
fV
AC
AC
where
are the imaginary parts of the measured currents,
f
is
the frequency of the AC source, and V
AC
is the AC voltage amplitude. The time-
variant transition coefficients
K
pu
and
K
pd
were obtained according to the 2EQ/2UK
and
ℑ
(
I
)
ℑ
(
I
)
VCC
gnd
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