Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
1999-11-19
2001-07-24
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S112000, C327S374000, C327S377000, C326S082000, C326S087000
Reexamination Certificate
active
06265914
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to high performance data transceivers and, more particularly, to a predriver for driving the input of a high speed output driver.
Data transceivers are used in a variety of computer systems and communication networks for transmitting data between various components of the system. As data throughput requirements continue to increase, data transmission frequencies continue to increase. For example, output drivers having a low output voltage swing, such as Gunning Transceiver Logic (GTL/GTL+) drivers, have been developed for driving high performance processor system buses and computer system backplanes. A basic GTL+ output driver includes a low impedance open drain N-channel metal oxide semiconductor (NMOS) transistor, which drives the receivers attached to the system bus through an incident wave switching interface. The NMOS driver transistor drives the incident wave with sufficient amplitude to switch the logic states of the receivers. External pull-up resistors are used to terminate the system bus transmission lines and to provide a pull-up current path when the NMOS driver transistor is off.
A predriver circuit is typically used to drive the input to the NMOS driver transistor at a high frequency. A traditional GTL+ predriver circuit is configured as a logic NOR gate, with additional circuitry to speed the rise and fall times of the predriver output. At high frequencies, it is difficult for the predriver output to maintain an full “rail-to-rail” voltage swing. In particular, it is difficult for the predriver to drive its output completely to zero volts before the output is charged back up again with the next data transition. At higher frequencies, the low voltage output of the predriver can rise close to the threshold voltage of NMOS driver transistor. The NMOS driver transistor may not turn off completely, which can result in undesirable leakage current through the transistor or unintended switching at the receivers. If the predriver output discharges more quickly, thus reaching a lower voltage, the faster discharge can cause greater overshoots and ringbacks at high frequencies.
Improved predrivers which are capable of driving an output voltage rail-to-rail within the desired frequency while controlling overshoots and ringback are desired.
SUMMARY OF THE INVENTION
One aspect of the present invention relates to a predriver for driving an output data buffer at high frequencies. The predriver includes a data input, a data output, a first voltage pull-up circuit, a first voltage pull-down circuit, a delay circuit and a second voltage pull-down circuit. The first voltage pull-up circuit is coupled to the data output and has a control terminal coupled to the data input. The first voltage pull-down circuit is coupled to the data output and has a control terminal coupled to the data input. The first voltage pull-down circuit, when active, is adapted to at least temporarily hold the data output above a selected voltage. The delay circuit is coupled to the data input. The second voltage pull-down circuit is coupled to the data output and has a control terminal coupled to an output of the delay circuit.
Another aspect of the present invention relates to a data transmission apparatus, which includes a transmission line, a termination resistance and an output driver. The termination resistance and the output driver are coupled to the transmission line. The predriver includes a data input for receiving a data transition and a data output, which is coupled to the output driver. The predriver partially discharges the data output from a logic high level to a logic low level in response to the data transition received on the data input. The predriver then further discharges the data output after a time delay measured from the data transition.
Yet another aspect of the present invention relates to a method of driving an output driver input at high frequencies in a data transmission system. The method includes receiving a data signal having a first transition from a first logic state to a second, different logic state. The output driver input is partially discharged in response to the first transition. The output driver input is then further discharged in response to the first transition, after waiting a time delay measured from the first transition.
REFERENCES:
patent: 4777389 (1988-10-01), Wu et al.
patent: 5168176 (1992-12-01), Wanlass
patent: 5206545 (1993-04-01), Huang
patent: 5306965 (1994-04-01), Asprey
patent: 5362997 (1994-11-01), Bloker
patent: 5410189 (1995-04-01), Nguyen
patent: 5410262 (1995-04-01), Kang
patent: 5898326 (1999-04-01), Okayasu
patent: 5963047 (1999-10-01), Kwong et al.
National Semiconductor Product Data Sheet LM3460, “Precision Controller for GTLp and GTL Bus Termination,” Oct. 21, 1999. http://www.national.com/pf/LM/LM3460.html.
Faichild Semiconductor Product Data Sheet GTLP8T306, “8-Bit LVTTL-to-GTLP Bus Transceiver”, Oct. 21 1999. http://www.fairchildsemi.com/pf/GT/GTLP8T306.html.
Texas Instruments Product Data Sheet, “Digital Logic Technology Families: GTL Gunning Transceiver Logic”, May 16, 1999, pp 1-3 http://www.ti.com/sc/docs/products/logic/families/gtl.htm.
Intel AP-827 Application Note, 100 MHz GTL+ Layout Guidelines for the Pentium® II Processor and Intel 440BX AGPset, May 12, 1999, 6-15. http://developer.intel.com/design/PentiumII/applnots/24373501.pdf.
Callahan Timothy P.
LSI Logic Corporation
Luu An T.
LandOfFree
Predriver for high frequency data transceiver does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Predriver for high frequency data transceiver, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Predriver for high frequency data transceiver will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2522749