Eye modulation for pulse-amplitude modulation communication systems
View Patent ↗The present invention is directed to communication systems. More specifically, embodiments of the present invention provide a technique and system thereof for performing eye modulation. Eye modulation is performed at the transmission side of a PAM communication system to compensate for distortion and non-linearity and generate an output waveform. Spacing among eye levels is adjusted by performing symmetric modulation using α parameter and asymmetric modulation using β parameter. A correction module measures the output waveform and sends feedback signals to a control module to adjust the α parameter and the β parameter. There are other embodiments as well.
1. A communication system comprising:
a control module being configured to generate a first control signal for adjusting an α parameter and a second signal for adjusting a β parameter, the α parameter and the β parameter being determined based on eye-modulation characteristics;
a PAM transmitter being configured to perform eye-modulation on a source data and generate an output waveform using the α parameter and the β parameter, the α parameter being used to adjust a middle eye-height, the β parameter being used to adjust a top eye-height and a bottom eye-height, the source data comprising MSB data and LSB data, the top eye-height separating a first eye level and a second eye level, the middle eye-height separating the second eye level and a third eye level, and the bottom eye-height separating the third eye level and a fourth eye level; and
a correction module being configured to measure eye-modulation characteristics, the eye-modulation characteristics including distortion and signal-to-noise ratios.
2. The system of claim 1 wherein the PAM transmitter comprises an optical driver, the signal-to-noise ratios of the output waveforms being measured from an output of the optical driver.
3. The system of claim 1 wherein adjusting the middle-eye height is associated symmetric eye-modulation for compensating distortion in a data path.
4. The system of claim 1 wherein adjusting the top eye-height and the bottom eye height is associated asymmetric eye-modulation for equalizing signal-to-noise ratios corresponding to the first, second, third, and fourth eye levels.
5. The system of claim 1 wherein the PAM transmitter adjusts the α parameter using the first signal and the β parameter using the second signal.
6. The system of claim 1 further comprising a phase-lock loop for providing clock signal to the PAM transmitter.
7. The system of claim 1 wherein the control module comprises a memory for storing calibration data used for calibrating the α parameter and the β parameter.
8. The system of claim 1 wherein the PAM transmitter further comprises a DC source coupled to the data lanes.
9. The system of claim 1 wherein the wherein the output waveform comprises PAM4 signals.
10. The system of claim 1 wherein the PAM transmitter is configured to modulate the source data using a set of predetermined formulae involving the α parameter and the β parameter.
11. The system of claim 1 wherein a function of the MSB data XOR the LSB data is modified by the β parameter.
12. The system of claim 1 wherein a function of the MSB data is modified by the α parameter.
13. The system of claim 1 wherein a function of the LSB data is modified by the α parameter.
14. A method for calibrating eye-modulation parameters in a PAM4 communication system, the method comprising:
retrieving calibration data for determining an α parameter and a β parameter;
performing PAM4 eye-modulation with four eye levels to generate an output waveform, the four eye levels being separated by a top eye height, a middle eye height, and a bottom eye height;
measuring the eye heights and signal-to-noise ratios of the output waveform, the signal-to-noise ratios being corresponding to the eye heights;
adjusting the α parameter to equalize the middle eye height relative to the top eye height and the bottom eye height; and
adjusting the β parameter to equalize signal-to-noise ratios by changing the top eye height and the bottom eye.
15. The method of claim 14 wherein the bottom eye height comprises a spacing between LSB levels.
16. The method of claim 14 wherein the top eye height comprises a spacing between MSB levels.
17. The method of claim 14 wherein the adjusting the β parameter comprises changing the β parameter until signal-to-noise ratios of the four eye levels are substantially equal.
18. The method of claim 14 wherein the adjusting the α parameter is associated reducing distortion in a data path.
19. A communication system comprising:
a control module being configured to generate a first control signal for determining an α parameter and a second signal for determining a β parameter, the α parameter and the β parameter being determined based on eye-modulation characteristics, the control module comprising a memory for storing calibration data;
a PAM4 transmitter being configured to perform eye-modulation on the calibration data and generate an output waveform using the α parameter and the β parameter, the output waveform being modulated with four eye levels, the α parameter being used to adjust a middle eye-height, the β parameter being used to adjust a top eye-height and a bottom eye-height, the calibration data comprising MSB data and LSB data, the output waveform being outputted by an optical driver; and
a correction module being configured to measure eye-modulation characteristics, the eye-modulation characteristics including distortion and signal-to-noise ratios.
20. The system of claim 19 wherein the top eye-height comprises a spacing between MSB data eye levels and the bottom eye-height comprises a spacing between LSB data eye levels.