Clock recovery for data signals
Embodiments of the present invention provide improved techniques for recovering clock information from data signals. In one embodiment, a general purpose device such as a real-time oscilloscope acquires a data signal. The device takes a derivative of the data signal, then computes the square or absolute of the derivative before applying a bandpass filter. The bandpass filter is a windowing function a spectrum that is wider than the clock, and has a flat top and smooth transitions on both sides. In one embodiment, at Tukey window may be used. The device finds edge crossing times of the filtered result, and applies a phase-locked loop or lowpass filter to the edge crossing times in order to recover a stable clock signal. When the improved techniques are implemented in software, they may be used with any number of different equalizers that are required by various high-speed serial data link systems.
1. A test instrument configured to recover a clock signal from a data signal, the instrument comprising:
a physical interface for acquiring data signal information from the data signal;
memory configured to store:
the data signal information;
a recovered clock signal; and
software instructions for performing a clock recovery method, the method comprising:
computing a derivative of the data signal information;
computing a square or absolute of the derivative;
obtaining a filtered result by applying a bandpass filter to the square or absolute;
finding one or more edge crossing trifles of the filtered result;
filtering the one or more edge crossing times to obtain a recovered clock signal; and
storing the recovered clock signal in the memory; and
a processor configured to execute the software instructions.
2. The test instrument of claim 1 , wherein filtering the one or more edge crossing times to obtain a recovered clock signal comprises applying a phase-locked loop.
3. The test instrument of claim 1 , wherein filtering the one or more edge crossing times to obtain a recovered clock signal comprises applying a lowpass filter.
4. The test instrument of claim 1 , further comprising a display configured to display the recovered clock signal.
5. The test instrument of claim 1 , wherein the bandpass filter comprises a windowing function.
6. The test instrument of claim 5 , wherein the windowing function is a Tukey window.
7. The test instrument of claim 1 , wherein the memory is further configured to store software instructions for applying a linear equalizer to the data signal information.
8. The test instrument of claim 7 , wherein the linear equalizer is selected from the group consisting of de-emphasis, pre-emphasis, CTLE, and FFE equalizers.
9. A method for recovering a clock signal from a data signal, the method comprising:
acquiring a data signal at a device, using a physical interface on the device;
extracting data signal information from the data signal;
computing a derivative of the data signal information;
computing a square or absolute of the derivative;
applying a bandpass filter to the square or absolute, to obtain a filtered result;
finding one or more edge crossing times of the filtered result;
filtering the one or more edge crossing times, to obtain a recovered clock signal; and
storing the recovered clock signal in memory.
10. The method of claim 9 , wherein the step of filtering the edge crossing times comprises applying a phase-locked loop.
11. The method of claim 9 , wherein the step of filtering the edge crossing times comprises applying a lowpass filter.
12. The of claim 9 , wherein the bandpass filter comprises a windowing function.
13. The method of claim 12 , wherein the windowing function is a Tukey window.
14. The method of claim 9 , wherein the step of acquiring a data signal further comprises applying a linear equalizer to the acquired data signal to partially compensate the channel loss.
15. The method of claim 14 , wherein the linear equalizer is selected from the group consisting of de-emphasis, pre-emphasis, CTLE, and FFE equalizers.
16. Anon-transitory computer readable medium containing computer executable instructions which, when executed by a processor, perform a method for recovering a clock signal from a data signal, the method comprising:
acquiring the data signal from a physical interface;
extracting data signal information from the data signal;
computing a derivative of the data signal information;
computing a square or absolute of the derivative;
applying a bandpass filter to square or absolute, to obtain a filtered result;
finding one or more edge crossing times of the filtered result;
filtering the one or more edge crossing times to obtain a recovered clock signal; and
storing the recovered clock signal in memory.
17. The non-transitory computer readable medium of claim 16 , wherein the step of filtering the edge crossing times to obtain a clock signal comprises applying a phase-locked loop.
18. The non-transitory computer readable medium of claim 16 , wherein the step of filtering the edge crossing times to obtain a clock signal comprises applying a lowpass filter.
19. The non-transitory computer readable medium of claim 16 , wherein the step of applying a bandpass filter to the square or absolute, to obtain a filtered result comprises applying a windowing function.
20. The non-transitory computer readable medium of claim 19 , wherein the windowing function is a Tukey window.
21. The non-transitory computer readable medium of claim 16 , wherein the step of acquiring a data signal through a physical interface further comprises applying a linear equalizer to the acquired data signal to partially compensate the channel loss.
22. The non-transitory computer readable medium of claim 21 , wherein the linear equalizer is selected from the group consisting of de-emphasis, pre-emphasis, CTLE, and FFE equalizers.