146
Digital Electronics
Figure 5.30 Example 5.5.
Schottky TTL
Low Power
Schottky TTL
Standard TTL
2
3
4
1
Standard TTL
Figure 5.31 Example 5.6.
Table 5.1 Example 5.6
Logic family
I IH (A) I OH (mA)
I IL (mA)
I OL (mA)
Standard TTL
40
0.4
1.6
16
LS-TTL
20
0.4
0.4
8.0
S-TTL
50
1.0
2.0
20
Solution
• In the HIGH-state:
– the gate 1 output sourcing capability = 400 A;
– the gate 2 input requirement = 50 × 4 = 200 A;
– the gate 3 input requirement = 20 × 2 = 40 A;
– the gate 4 input requirement = 40 × 4 = 160 A;
– the total input current requirement = 400 A;
– therefore, the fan-out is not exceeded in the HIGH state.