On-chip bathtub BER measurement for high-speed serdes diagnostics

1. A method for evaluating operation of a receiver, the receiver including: an analog front end for receiving a serial input signal and generating a pre-processed signal; a plurality of samplers connected in parallel to the analog front end for sampling the pre-processed signal, the plurality of samplers comprising a plurality of utility samplers, a plurality of data samplers and a plurality of timing samplers; an unrolled decision feedback equalizer (UDFE) connected to outputs of the plurality of data samplers; and a serial input parallel out (SIPO) block connected to an output of the UDFE and outputs of the plurality of utility samplers and the plurality of timing samplers for generating a parallel output signal, the method comprising:

adjusting settings of the plurality of utility samplers to sweep across a range of interest, where a number of utility samplers swept across the range of interest is equal to a number of the plurality of data samplers;

at each of a plurality of points spanning the range of interest, comparing a selected output of one of the plurality of utility samplers at that point to an output of one of the plurality of data samplers to detect an error event; and,

accumulating the error events for the plurality of points spanning the range of interest.

2. The method of claim 1 comprising adjusting timing offsets of the plurality of utility samplers to sweep horizontally across the range of interest at a plurality of voltage threshold levels to determine a horizontal bathtub.

3. The method of claim 2 wherein the range of interest spans timing offsets across an entire signal unit interval.

4. The method of claim 2 wherein the horizontal sweep starts at a timing point of −0.5 UI with respect to a sampling point and moves to the centre of the eye until a number of detected error events drops to zero, and then proceeds to a timing point of +0.5 UI with respect to a sampling point and moves to the centre of the eye until the number of detected error event drops to zero.

5. The method of claim 1 comprising adjusting voltage thresholds of the plurality of utility samplers to sweep vertically across the range of interest to determine a vertical bathtub.

6. The method of claim 5 comprising adjusting the voltage thresholds from a maximum positive signal amplitude to zero and from a maximum negative signal amplitude to zero.

7. The method of claim 5 comprising adjusting the voltage thresholds from a median positive signal amplitude to zero, from the median positive signal amplitude up to a maximum positive amplitude, from a median negative signal amplitude to zero and from the median negative signal amplitude to a maximum negative signal amplitude.

8. The method of claim 5 comprising adjusting the voltage thresholds from a maximum positive signal amplitude downwardly until a number of detected error events drops to zero and from a maximum negative signal amplitude upwardly until the number of detected error events drops to zero.

9. The method of claim 5 comprising adjusting the voltage thresholds from a median positive signal amplitude downwardly until a number of detected error events drops to zero, from the median positive signal amplitude upwardly until the number of detected error events drops to zero, from a median negative signal amplitude downwardly until the number of detected error events drops to zero, and from the median negative signal amplitude upwardly until the number of detected error events drops to zero.

10. A receiver comprising:

an analog front end for receiving a serial input signal and generating a pre-processed signal;

a plurality of samplers connected in parallel to the analog front end for sampling the pre-processed signal, the plurality of samplers comprising a plurality of utility samplers, a plurality of data samplers and a plurality of timing samplers;

an unrolled decision feedback equalizer (UDFE) connected to outputs of the plurality of data samplers;

a serial input parallel out (SIPO) block connected to an output of the UDFE and outputs of the plurality of utility samplers and the plurality of timing samplers for generating a parallel output signal; and,

a diagnostic circuit connected to the output of the UDFE and outputs of the plurality of utility samplers and connected to control the utility samplers to:

adjust settings of the plurality of utility samplers to sweep across a range of interest, where a number of utility samplers swept across the range of interest is equal to a number of the plurality of data samplers;

at each of a plurality of points spanning the range of interest, compare a selected output of one of the plurality of utility samplers at that point to an output of one of the plurality of data samplers to detect an error event; and,

accumulate the error events for the plurality of points spanning the range of interest.

11. The receiver of claim 10 wherein the diagnostic circuit adjusts timing offsets of the plurality of utility samplers to sweep horizontally across the range of interest at a plurality of voltage threshold levels to determine a horizontal bathtub.

12. The receiver of claim 11 wherein the range of interest spans timing offsets across an entire signal unit interval.

13. The receiver of claim 11 wherein the horizontal sweep starts at a timing point of −0.5 UI with respect to a sampling point and moves to the centre of the eye until a number of detected error events drops to zero, and then proceeds to a timing point of +0.5 UI with respect to a sampling point and moves to the centre of the eye until the number of detected error event drops to zero.

14. The receiver of claim 10 wherein the diagnostic circuit adjusts voltage thresholds of the plurality of utility samplers to sweep vertically across the range of interest to determine a vertical bathtub.

15. The receiver of claim 14 wherein the diagnostic circuit adjusts the voltage thresholds from a maximum positive signal amplitude to zero and from a maximum negative signal amplitude to zero.

16. The receiver of claim 14 wherein the diagnostic circuit adjusts the voltage thresholds from a median positive signal amplitude to zero, from the median positive signal amplitude up to a maximum positive amplitude, from a median negative signal amplitude to zero and from the median negative signal amplitude to a maximum negative signal amplitude.

17. The receiver of claim 14 wherein the diagnostic circuit adjusts the voltage thresholds from a maximum positive signal amplitude downwardly until a number of detected error events drops to zero and from a maximum negative signal amplitude upwardly until the number of detected error events drops to zero.

18. The receiver of claim 14 wherein the diagnostic circuit adjusts the voltage thresholds from a median positive signal amplitude downwardly until a number of detected error events drops to zero, from the median positive signal amplitude upwardly until the number of detected error events drops to zero, from a median negative signal amplitude downwardly until the number of detected error events drops to zero, and from the median negative signal amplitude upwardly until the number of detected error events drops to zero.

19. A method for controlling a receiver, the receiver including: an analog front end for receiving a serial input signal and generating a pre-processed signal; a plurality of samplers connected in parallel to the analog front end for sampling the pre-processed signal, the plurality of samplers comprising a plurality of utility samplers, a plurality of data samplers and a plurality of timing samplers; an unrolled decision feedback equalizer (UDFE) connected to outputs of the plurality of data samplers; and a serial input parallel out (SIPO) block connected to an output of the UDFE and outputs of the plurality of utility samplers and the plurality of timing samplers for generating a parallel output signal, the method comprising:

adjusting settings of the plurality of utility samplers to sweep timing offsets across a range of interest within a signal unit interval at a plurality of voltage levels;

at each of a plurality of points spanning the range of interest, comparing a selected output of one of the plurality of utility samplers at that point to an output of one of the plurality of data samplers to detect an error event;

determining a horizontal bathtub based on the error events for the plurality of points spanning the range of interest; and

adjusting a timing offset of the data samplers from a midpoint of the signal unit interval based on the horizontal bathtub.