Digital Signal Processing Reference
In-Depth Information
V
DD
- v
(
extracted
)
=
v
(
relative
)
V
DD
V
DD
v
v
Pull-up
i
i
V
DD
relative
i-v
curve
Extracted
i-v
curve
Figure 11-37
Construction of
V
DD
relative
i
-
v
curves.
2.5
2.0
Pull-up
turns off
1.5
1.0
50
Ω
Pull-up
turns on
0.5
0.0
−
0.5
0.0
2.0
4.0
6.0
8.0
10.0
Time (ns)
V
DD
3.0
Pull-down
turns on
2.5
50
Ω
2.0
1.5
Pull-down
turns off
1.0
0.5
0.0
0.0
2.0
4.0
6.0
8.0
10.0
Time (ns)
Figure 11-38
Voltage versus time curves for a push-pull IBIS model.
push-pull transmitter, a minimum of four
v
-
t
curves is desired, as shown in the
figure. All of the curves must be time correlated, which means that they start from
the same reference point in time. By specifying the curves in this manner, IBIS
models are able to capture the effects of separate switching for the pull-up and
pull-down devices. This is particularly useful for modeling “break-before-make”
circuits, such as the one studied in Problem 11.1, and also allows the support of
“multistaged” output drivers, which are described below.
Multistage drivers control the rise and fall times of the output by spreading out
switching of the pull-up and pull-down devices over time (Figure 11-39). These
models break the circuit into multiple pull-up and pull-down devices, which
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