Digital Signal Processing Reference
In-Depth Information
TABLE 11-2. Relation Between
v
in
and
v
GS
for the
Pull-up and Pull-down Devices of an Inverting
Transmitter
v
GS
(V)
v
in
(V)
NMOS
PMOS
0.0
0.0
−
2
.
5
0.5
0.5
−
2
.
0
−
1.0
1.0
1
.
5
−
1.5
1.5
1
.
0
2.0
2.0
−
0
.
5
2.5
2.5
0.0
TABLE 11-3. Logic Table for a Tristate Transmitter
en/en
v
in
v
out
0/
V
DD
X
High
Z
V
DD
/0
V
DD
0
V
DD
/0
0
V
DD
en
MP
1
v
in
v
out
MN
2
en
Figure 11-11
Tristate push-pull driver.
electrical characteristics will vary due to normal statistical variations in
the manufacturing process. In addition, MOSFET currents are sensitive to
environmental factors such as supply voltage (
i
D
increases as the
V
DD
increases)
and device temperature (
i
D
decreases with increasing
T
). As a result, the
current-voltage relationship for transistors can vary by a factor of 2 to 3 across
the process and environmental extremes, leading to wide swings in the output
impedance and rise-fall time. In the case of microprocessor-based systems,
where yearly volumes reach into the hundreds of millions, excessive variation in
the electrical characteristics can lead to failure of some of the systems to operate
at full performance.
Compensation
refers to techniques that minimize the
variation between different parts operating in different environments. Designers
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