Datasheet
SCEA022
7–261
Achieving Maximum Speed on Parallel Buses With Gunning Transceiver Logic (GTLP)
One curve represents a bus line in the unloaded state, for which the bus-side connectors are the
only loads on the line. The other curve represents a fully loaded bus line. The same correlation
also is produced with regard to the propagation time of the line, and is shown in Figure 4.
20
18
16
14
12
10
8
6
4
2
0
2 cm 3 cm
4 cm
5 cm 6 cm
2 inches1 inch
Slot Spacing
Propagation Delay – ns
7 cm
Line-Impedance Backplane
Unloaded Bus
†
Fully Loaded Bus
‡
†
Assuming a capacitive load of 2 pF per slot (connector only)
‡
Assuming a capacitive load of 10 pF per slot (complete module)
Figure 4. Effect of Slot Spacing on Flight Time
The values from Table 1 for the slot distance of 1 inch in Figures 3 and 4 can be found at
intersections with the dashed lines.
The homogeneity of the line impedance cannot be ensured in every case. For a backplane, the
modules can be inserted into different positions on the backplane, and some positions can be
left empty, so the different bus-line sections have different impedance values.
However, this fact does not significantly affect the quality of the signal.