Gunning transceiver logic

Gunning transceiver logic (GTL) is a type of logic signaling used to drive electronic backplane buses. It has a voltage swing between 0.4 volts and 1.2 volts — much lower than that used in TTL and CMOS logic — and symmetrical parallel resistive termination. The maximum signaling frequency is specified to be 100 MHz, although some applications use higher frequencies. GTL is defined by JEDEC standard JESD 8-3 (1993) and was invented by William Gunning while working for Xerox at the Palo Alto Research Center.

All Intel front-side buses use GTL. As of 2008, GTL in these FSBs has a maximum frequency of 1.6 GHz. The front-side bus of the Intel Pentium Pro, Pentium II and Pentium III microprocessors uses GTL+ (or GTLP) developed by Fairchild Semiconductor, an upgraded version of GTL which has defined slew rates and higher voltage levels. AGTL+ stands for either assisted Gunning transceiver logic or advanced Gunning transceiver logic. These are GTL signaling derivatives used by Intel microprocessors.

References

• "GTLP vs. GTL: A Performance Comparison from a System Perspective" (PDF), AN-1070, Fairchild Semiconductor, December 2000, archived from the original (PDF) on 2013-09-22, retrieved 2008-03-18
• "GTL/BTL: A Low-Swing Solution for High-Speed Digital Logic" (PDF), Application Note, Texas Instruments, 1997
• JEDEC Standard JESD8-3A, Gunning Transceiver Logic (GTL) Low-Level, High Speed Interface Standard for Digital Integrated Circuits (PDF), JEDEC, May 2007
• Steve Blozis (January 2001), Texas Instruments GTLP Frequently Asked Questions (PDF), Texas Instruments