Method and system for crosstalk cancellation
Signals propagating in one communication channel can generate crosstalk interference in another communication channel. A crosstalk cancellation device can process the signals causing the crosstalk interference and generate a crosstalk cancellation signal that can compensate for the crosstalk when applied to the channel receiving crosstalk interference. The crosstalk cancellation device can include a model of the crosstalk effect that generates a signal emulating the actual crosstalk both in form an in timing. The crosstalk cancellation device can include a controller that monitors crosstalk-compensated communication signals and adjusts the model to enhance crosstalk cancellation performance. The crosstalk cancellation device can have a mode of self configuration or calibration in which defined test signals can be transmitted on the crosstalk-generating channel and the crosstalk-receiving channel.
1. A signal processing system, for applying a crosstalk estimate to a first communication channel to compensate for crosstalk coupled into the first communication channel from a second communication channel, comprising:
a model, coupled to the second communication channel, operative to generate the crosstalk estimate, comprising:
a waveform shaper comprising a plurality of delay stages coupled to a plurality of respective amplifiers; and
an adjustable delay coupled to the waveform shaper; and
a controller, operative to process crosstalk compensated communication signals and adjust the waveform shaper and the adjustable delay.
2. The signal processing system of claim 1 , wherein the waveform shaper comprises a tapped delay line filter.
3. The signal processing system of claim 1 , wherein the adjustable delay receives input from the waveform shaper.
4. The signal processing system of claim 1 , wherein the adjustable delay provides input to the waveform shaper.
5. The signal processing system of claim 1 , wherein the model further comprises a fixed filter, coupled to at least one of the waveform shaper and the adjustable delay, operative to transmit frequencies above a threshold frequency and attenuate frequencies below the threshold frequency.
6. The signal processing system of claim 1 , wherein the controller comprises a digital controller.
7. The signal processing system of claim 1 , wherein the controller is further operative to control transmission of signals having predetermined voltage patterns on the first and second communication channels.
8. The signal processing system of claim 1 , wherein the controller is operative to calibrate the model.
9. A method for processing a first communication signal having crosstalk from a second communication signal comprising the steps of:
sampling the second communication signal;
processing the sample of the second communication signal to generate a crosstalk emulation signal;
applying the crosstalk emulation signal to the first communication signal to cancel at least some of the crosstalk;
generating a third communication signal based on the application of the crosstalk emulation signal;
analyzing the third communication signal; and
adjusting the crosstalk emulation signal based on the analysis,
wherein the adjusting step comprises timing the crosstalk emulation signal to match the crosstalk.
10. The method of claim 9 , wherein:
the processing step comprises processing the sample with a model comprising at least one modeling parameter; and
the adjusting step further comprises adjusting the at least one modeling parameter.
11. The method of claim 9 , wherein:
generating the crosstalk emulation signal comprises generating a waveform differing from the crosstalk by a difference; and
the adjusting step further comprises reducing the difference.
12. The method of claim 9 , wherein: analyzing the third communication signal comprises monitoring for residual crosstalk in the third communication signal; and adjusting the crosstalk emulation signal further comprises reducing the residual crosstalk.
13. The method of claim 9 , wherein applying the crosstalk emulation signal to the first communication signal comprises subtracting the crosstalk emulation signal from the first communication signal.
14. A method for processing a first communication signal having crosstalk from a second communication signal comprising the steps of:
sampling the second communication signal;
processing the sample of the second communication signal to generate a crosstalk emulation signal;
applying the crosstalk emulation signal to the first communication signal to cancel at least some of the crosstalk;
generating a third communication signal based on the application of the crosstalk emulation signal;
analyzing the third communication signal; and
adjusting the crosstalk emulation signal based on the analysis, wherein:
the processing step comprises synchronizing the crosstalk emulation signal with the crosstalk to a level of synchronization; and
the adjusting step comprises improving the level of synchronization.
15. A signal processing method, comprising the steps of:
transmitting a test signal over a first communication channel;
coupling a portion of the test signal from the first communication channel into a second communication channel via a crosstalk effect;
defining a model of the crosstalk effect based on processing the portion of the test signal coupled into the second communication channel via the crosstalk effect;
transmitting a first communication signal over the first communication channel;
coupling a portion of the first communication signal into the second communication channel via the crosstalk effect;
transmitting a second communication signal over the second communication channel;
processing a portion of the first communication signal with the model and outputting an estimate of the portion of the first communication signal coupled into the second communication signal via the crosstalk effect; and
compensating for the crosstalk effect by applying the estimate to the second communication channel.
16. The method of claim 15 , wherein the step of transmitting the test signal over the first communication channel further comprises transmitting data on the first communication channel and providing an essentially uniform voltage on the second communication channel.
17. The method of claim 15 , wherein defining the model of the crosstalk effect comprises adjusting a modeling parameter of the model.
18. The method of claim 15 , wherein defining the model of the crosstalk effect comprises adjusting a signal delay of the model.
19. The method of claim 15 , wherein defining the model of the crosstalk effect comprises setting a gain of the model.
20. The method of claim 15 , wherein applying the estimate to the second communication channel comprises subtracting the estimate from the second communication signal and the portion of the first communication signal coupled into the second communication channel via the crosstalk effect.
21. A signal processing system, for correcting crosstalk coupled from a first communication channel into a second communication channel, comprising:
a modeling filter, coupled to the first communication channel, operative to generate an estimate of the crosstalk, comprising:
an adjustable analog filter, controllable by a modeling input; and
an adjustable delay coupled to the adjustable analog filter; and
an analysis circuit, operative to analyze crosstalk corrected signals and adjust the adjustable analog filter and the adjustable delay.
22. The signal processing system of claim 21 , wherein the analog filter comprises a tapped delay line filter.
23. The signal processing system of claim 21 , wherein the adjustable delay receives input from the analog filter.
24. The signal processing system of claim 21 , wherein the adjustable delay provides input to the analog filter.
25. The signal processing system of claim 21 , wherein the modeling filter further comprises a fixed filter, coupled to at least one of the analog filter and the adjustable delay, operative to transmit frequencies above a threshold frequency and attenuate frequencies below the threshold frequency.
26. The signal processing system of claim 21 , wherein the analysis circuit comprises a digital controller.
27. The signal processing system of claim 21 , wherein the analysis circuit is further operative to control transmission of signals having predetermined voltage patterns on the first and second communication channels.
28. The signal processing system of claim 21 , wherein the analysis circuit is further operative to calibrate the modeling filter.
29. An apparatus, for correcting crosstalk in a data communications system, comprising:
a crosstalk modeling filter that models a crosstalk response;
a difference node that subtracts the modeled crosstalk response from a communication signal, comprising the crosstalk, to yield a crosstalk-compensated signal, and
a control circuit that processes the crosstalk-compensated signal and adjusts the crosstalk modeling filter to reduce residual crosstalk in the crosstalk-compensated signal.
30. The apparatus of claim 29 , wherein the crosstalk modeling filter comprises an adjustable delay filter and an analog tapped delay line filter.
31. The apparatus of claim 30 , wherein the adjustable delay filter circuit comprises a digital circuit that receives a data signal causing the crosstalk and amplitude limits the data signal.
32. The apparatus of claim 30 , wherein the crosstalk modeling filter further comprises a first-order high-pass filter.
33. The apparatus of claim 29 , wherein the control circuit comprises an analog low-pass filter, an analog-to-digital converter, and a digital controller.
34. The apparatus of claim 33 , wherein the data communications system communicates data at a baud rate and the analog-to-digital converter operates at a speed lower than the baud rate.
35. The apparatus of claim 33 , wherein the data communication system transmits data at a baud rate and the digital controller operates at a speed less than baud rate.
36. The apparatus of claim 33 , wherein a device that measures signal magnitude based on signal amplitude provides input to the analog low-pass filter.
37. The apparatus of claim 36 , wherein the device comprises a power-detector.
38. The apparatus of claim 36 , wherein the device comprise a full-wave rectifier.
39. The apparatus of claim 36 , wherein the device comprises a half-wave rectifier.
40. The apparatus of claim 36 , wherein a spectral weighting filter provides input to the device.
41. The apparatus of claim 33 , wherein the control circuit comprises a finite state machine.
42. The apparatus of claim 33 , wherein the control circuit comprises a microprocessor.