HD74AC HITACHI [Hitachi Semiconductor], HD74AC Datasheet - Page 42

• Manufacturer Part Number: HD74AC
• Description: HD74AC Series Common Information
• Manufacturer: HITACHI [Hitachi Semiconductor]

With over 2.0 V of noise margins, the FACT family offers better noise rejection than any other comparable
technology.
In any design, the distance that lines run adjacent to each other should be kept as short as possible. The
best situation is when the lines are perpendicular to each other. For those situations where lines must run
parallel, the effects of crosstalk can be minimized by line termination. Terminating a line in its
characteristic impedance reduces the amplitude of an initial crosstalk pulse by 50%. Terminating the line
will also reduce the amount of ringing (figure 15). Crosstalk problems can also be reduced by moving lines
further apart or by inserting ground lines or planes between them.
Signal on Active Line
Passive Line
Gnd
Figure 15 Effects of Termination on Crosstalk
A
V
R
T
Z
O
Figure 14 Low Noise Margin
Vn = Coupled Signal
V
70%
CC
3
2
1
0
0 5 10 15 20 25
Volts
Noise Amplitude at A
Pulse Width (ns)
Versus R
HAZARD
SAFE
30 35 40 45 50
100% : N
67% : R = 2Z
60% : R = 1.5Z
50% : R = Z
V
CC
V
Design Considerations
R+Z
= 5.0 V
R
O
O
R
O
O
O
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