Method and apparatus for high speed bus having adjustable, symmetrical, edge-rate controlled, waveforms

1. A method of enhancing noise margin on digital signal lines comprising the steps of:

evaluating impedances and lengths of a plurality of digital signal lines;

determining resonances of each of the digital signal lines;

determining waveforms for each digital signal line optimized for noise margin; and

generating a configuration for at least one programmable device driver to configure said device driver to generate at least one waveform optimized for noise margin.

2. The method of claim 1 , wherein the waveforms determined in the step of determining waveforms comprise symmetrical segments of smoothed and superimposed sinusoidal and trapezoidal waveforms.

3. The method of claim 1 wherein the digital signal lines are lines of a bus having a plurality of lines, and wherein separate configurations are generated for a plurality of programmable device drivers.

4. The method of claim 1 wherein the step of determining waveforms further comprises the step of performing circuit simulations to determine noise margins available with at least one waveform.

5. The method of claim 4 , wherein the at least one driver comprises a plurality of current-controlling devices for segments of piecewise-linear transitions and logic capable of sequencing segments during transitions.

6. The method of claim 5 , wherein the logic capable of sequencing segments during transitions further comprises a memory.

7. An integrated circuit for use in a system, the integrated circuit comprising:

bus drivers capable of driving a multidrop bus, the bus drivers further comprising means for driving lines of the multidrop bus with a waveform approximating a blend of trapezoidal and sinusoidal edge shapes,

wherein the bus drivers are configurable to generate a plurality of waveforms.

8. The integrated circuit of claim 7 , where the bus drivers are capable of driving at least one bus line with a signal having edge voltages approximating the equation V=c*((n*a*t)+(b*sin(nt))/(a+b) for a range of −1/n<=t<=1/n centered on the transition, where a and b are blending constants, c an amplitude, and t is time.

9. The integrated circuit of claim 7 , wherein the integrated circuit further comprises means for selecting a particular waveform of the plurality of waveforms for use during system operation.

10. The integrated circuit of claim 9 , wherein the particular waveform is selected to maximize noise margin at receivers coupled to the multidrop bus.

11. A bus driver for an integrated circuit capable of outputting a piecewise-linear approximation of an output waveform comprising:

a plurality of current-controlling devices for segments of piecewise-linear transitions and

logic capable of sequencing segments during transitions, the logic capable of sequencing segments during transitions further comprising a memory.

12. The bus driver of claim 11 , wherein the logic capable of sequencing segments during transitions further comprises a delay-locked loop.

13. The bus driver of claim 11 , wherein the memory of the logic capable of sequencing segments during transitions contains a configuration determined to control reflections for a particular bus configuration.

14. The bus driver of claim 13 , wherein the configuration determined to control reflections for a particular bus configuration produces signal edges approximating a blend of trapezoidal and gated-sinusoidal edges.