Threshold adjust system and method
An adaptive algorithm is implemented that optimizes the slicer threshold by optimizing the tail distribution of a “+1” and “−1” histogram. Through the use of a low resolution and under-sampled ADC, a histogram of received bit may be created. The difference between the y-intersects of lines derived from the “+1” and “−1” histogram is used to determine an error function. The algorithm iteratively updates the threshold value based on this error function.
1. A threshold adjustment method employed by a communications apparatus, the method comprising:
receiving an analog signal;
adjusting a threshold of the received analog signal in accordance with a threshold adjust signal to generate a threshold adjusted signal;
sampling the threshold adjusted signal to generate a sampled signal;
generating a histogram from the sampled signal;
processing the histogram to generate an error signal,
wherein processing includes calculating a difference between y-intersects of at least two substantially straight curves defined by log values from the histogram, wherein the y-axis represents the distribution of the received signal; and
generating the threshold adjust signal in accordance with the error signal.
2. The method of claim 1 comprising determining a threshold value in accordance with the difference between y-intersects.
3. The method of claim 1 wherein the sampling comprises under-sampling.
4. The method of claim 1 wherein the sampling comprises using a two-bit analog to digital converter.
5. The method of claim 1 wherein generating the threshold adjust signal comprises iteratively adjusting the threshold adjust signal.
6. The method of claim 1 wherein an optimum value for the threshold adjust signal is defined in accordance with a zero error function.
7. The method of claim 1 wherein adjusting the threshold associated with the received signal comprises adjusting a DC component of the received signal.
8. The method of claim 1 wherein processing comprises generating the error signal in accordance with at least one tail distribution defined by the histogram.
9. The method of claim 8 comprising providing at least one adaptation loop for adjusting signal quality of at least one of the received signal and the threshold adjusted signal in accordance with at least one error signal that is not based on a tail distribution.
10. The method of claim 9 wherein the at least one error signal comprises a squared error signal derived from the sampled signal.
11. A communications system comprising:
a threshold adjust circuit configured to adjust a threshold of a received signal in accordance with a threshold adjust signal to generate a threshold adjusted signal;
an analog to digital converter configured to sample the threshold adjusted signal in accordance with a clock signal to generate a sampled signal; and
a threshold adjust loop configured to:
generate a histogram from the sampled signal;
calculate a difference between y-intersects of at least two substantially straight curves defined by log values from the histogram, wherein the y-axis represents the distribution of the received signal;
process the histogram to generate an error signal; and
generate the threshold adjust signal in accordance with the error signal.
12. The system of claim 11 wherein the threshold adjust loop is configured to determine a threshold value in accordance with the difference between y-intersects.
13. The system of claim 11 wherein the threshold adjust loop is configured to iteratively adjust the threshold adjust signal.
14. The system of claim 11 wherein the analog to digital converter comprises a two-bit analog to digital converter.
15. The system of claim 11 wherein an optimum value for the threshold adjust signal is defined in accordance with a zero error function.
16. The system of claim 11 wherein the threshold adjust circuit is configured to adjust a DC component of the received signal to generate the threshold adjusted signal.
17. The system of claim 11 wherein the threshold adjust loop comprises at least one data memory for storing the histogram.
18. The system of claim 11 comprising a slicer configured to slice the threshold adjusted signal in accordance with a slicer threshold.
19. The system of claim 11 wherein the threshold adjust loop is configured to generate the error signal in accordance with at least one tail distribution defined by the histogram.
20. The system of claim 19 comprising at least one adaptation loop for adjusting signal quality of at least one of the received signal and the threshold adjusted signal in accordance with at least one error signal that is not based on a tail distribution.
21. The system of claim 20 wherein the at least one error signal comprises a squared error signal derived from the sampled signal.
22. A communications apparatus comprising:
receiving means for receiving an analog signal;
adjusting means for adjusting a threshold of the received analog signal in accordance with a threshold adjust signal to generate a threshold adjusted signal;
sampling means for sampling the threshold adjusted signal to generate a sampled signal;
histogram generating means for generating a histogram from the sampled signal;
processing means for processing the histogram to generate an error signal,
wherein the processing means includes a calculating means for a difference between y-intersects of at least two substantially straight curves defined by log values from the histogram, wherein the y-axis represents the distribution of the received signal; and
signal generating means for the threshold adjust signal in accordance with the error signal.
23. The apparatus of claim 22 comprising determining means for determining a threshold value in accordance with the difference between y-intersects.
24. The apparatus of claim 22 wherein comprising at least one adaptation loop for adjusting signal quality of at least one of the received signal and the threshold adjusted signal in accordance with at least one error signal that is not based on a tail distribution defined by the histogram.
25. The apparatus of claim 22 wherein the error signal comprises a squared error signal derived from the sampled signal.