Datasheet

7–57
Abstract
Results from a system that demonstrates the performance of GTL+ devices in a backplane are provided. The Texas Instruments
(TI) GTL16622A is the example used in the design of the physical backplane. The TI backplane demonstration system is
a useful tool for designers in understanding issues related to loading effects, termination, signal integrity, and data-transfer rate
in a high-performance backplane environment. Simulation results are compared to laboratory measurements to validate the
performance of TI GTL+ devices, and simulation results for the new TI GTL16612A in a very high-performance backplane
are provided.
Introduction
High-performance backplane is becoming common terminology in the rapidly evolving data-communications market.
Designers are developing innovative methods for multiplexing data to achieve higher throughput on the system bus or
backplanes. High-speed backplanes that can handle large amounts of data are extremely important to high-performance
systems.
The backplane is a physical and electrical interconnection between various modules in a system. Each module in the backplane
communicates with other modules through the backplane bus. The backplane traces and the load capacitance affect signal
integrity.
The discussion of the backplane demonstration system in this application report describes the various issues that should be
considered while designing a backplane. The type of termination, backplane topology and layout, connector capacitance and
stub lengths, along with the effect of the number of loads, all are investigated in this report. This report explains a demonstration
backplane and its elements, followed by results that have been obtained using the TI GTL+ devices. HSPICE, a simulation
tool, is used to model the performance of the system and to compare it to the hardware.
Background
In the past, increased throughput was achieved by increasing the frequency, or clock rate, or by increasing the bit width of the
bus. Logic families that were used as backplane drivers included Advanced BiCMOS Technology (ABT), Fast CMOS
Technology (FCT), Advanced CMOS Technology (ACT) and Backplane Transceiver Logic (BTL). These backplane drivers
do not perform well in backplanes operating at frequencies over 33 MHz, but are sufficient for lower throughput requirements.
With the trend toward higher system bandwidth requirements, into the hundreds of multimegabits per second, using a
technology that supports these higher performance requirements is essential.
These increased speeds and performance requirements in designs created a need for higher-speed devices. Newer technologies
developed by TI have helped to create devices that can drive these high-performance backplanes.
GTL/GTL+
Gunning Transceiver Logic (GTL), a technology invented by William Gunning at Xerox Corporation and standardized by
JEDEC, was a low-swing input/output (I/O) driver technology that helped address these high-performance requirements. This
technology was further modified by Intel and TI by increasing the voltage swing to create the GTL+ switching standard (see
Figure 1). Subsequently, the standard was used by TI and Fairchild to create stand-alone devices to drive backplanes.
Intel is a trademark of Intel Corporation.
TI is a trademark of Texas Instruments Incorporated.