Datasheet

7–209
Introduction
BTL (IEEE 1194.1-1991) and Futurebus designs offer significant performance advantages over conventional TTL backplane
implementations, but these advantages come with trade-offs. Switching noise in the form of ground bounce and EMI must be
controlled, and proper termination schemes must be employed to ensure signal integrity in this high-speed switching
environment. Trade-offs for price in the form of total system solution versus overall system performance are also of concern. This
paper begins with the historical perspective on signal-integrity issues addressed by the IEEE and follows with new pioneering
bus-interface solutions to help reduce overall BTL or Futurebus system costs and design complexities.
Current Generation of BTL/Futurebus Transceivers
A number of suppliers have developed BTL and Futurebus transceiver solutions that comply with IEEE 1194.1. These devices
share the same reduced output swing and tight switching thresholds shown in Figure 1 and a slew-rate control (see Figure 2). The
various devices differ considerably in wafer-fab process technology, propagation-delay performance, and other performance
metrics (see Table 1).
1 V
1.1 V
1.47 V
1.55 V
1.62 V
0.4 V
0.8 V
1.5 V
2 V
2.4 V
V
IH
V
t
V
IL
V
OL
V
OH
V
IH
V
t
V
IL
V
OL
5 VV
CC
0 VGND
5-V TTL
BTL/Futurebus
2.1 VV
OH
Figure 1. Comparison of TTL and BTL Switching Standards