Algorithm for finding the eye crossing level of a multilevel signal

• US 6,614,434 B1
• Filed: 06/14/2000
• Issued: 09/02/2003
• Est. Priority Date: 06/14/2000
• Status: Expired due to Fees

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Finke, Warren A.
• Primary Examiner(s): Bella, Matthew C.
• Assistant Examiner(s): BLACKMAN, ANTHONY J
• Application Number:
  US09/595,574
• Time in Patent Office: 1,175 Days
• Field of Search: 345/440, 324/624, 702/119, 702/67, 359/110, 359/180, 359/189, 375/226
• US Class Current: 345/440
• CPC Class Codes: H04L 1/205 jitter monitoring

Abstract

A method for controlling a digital oscilloscope locates a crossing level in an eye diagram (also including a crossing time), of a communications signal. The method includes the steps of locating the crossing time using a horizontal histogram box; and locating the crossing level using a vertical histogram box placed at a horizontal location substantially at the located crossing time.

Claims

1. A method for controlling a digital oscilloscope to locate a crossing level in an eye diagram of a communications signal, the eye diagram including an upper level and a lower level, a crossing time and a symbol time, comprising the steps of:

locating the upper level using a vertical histogram box;

locating the lower level using a vertical histogram box;

locating the crossing time by placing a horizontal histogram box centered at a vertical location substantially midway between the upper and lower levels having a width substantially corresponding to a symbol time, and a height substantially 20% or greater of the distance between the upper level and the lower level of the eye diagram; and

locating the crossing level using a vertical histogram box placed at a horizontal location substantially at the located crossing time.

2. The method of claim 1 wherein the height of the horizontal histogram box is substantially 20% of the difference between the upper level and the lower level of the eye diagram.

3. The method of claim 1 wherein the step of locating the crossing time further comprises the steps of:

accumulating histogram data corresponding to scans of the communications signal;

calculating the mean and standard deviation of the histogram data;

moving the horizontal histogram box vertically and repeating the accumulating and calculating steps until the standard deviation is minimized, then designating the horizontal location of the mean as the crossing time.

4. The method of claim 3, wherein the moving step comprises using a binary search algorithm to locate the vertical location of the horizontal histogram box having the minimum standard deviation.

5. The method of claim 3, wherein:

the step of locating the upper level comprises the steps of;

locating a vertical histogram box at a vertical position within respective minimum and maximum limits of the upper level and at a horizontal position in the neighborhood of the symbol time;

accumulating histogram data corresponding to scans of the communications signal;

calculating the mean and standard deviation of the histogram data; and

designating the vertical location corresponding to the mean as the upper level; and

the step of locating the lower level comprises the steps of;

locating a vertical histogram box at a vertical position within respective minimum and maximum limits of the lower level and at a horizontal position in the neighborhood of the symbol time;

accumulating histogram data corresponding to scans of the communications signal;

calculating the mean and standard deviation of the histogram data; and

designating the vertical location corresponding to the mean as the lower level.

6. The method of claim 1 wherein the step of locating the crossing level comprises the steps of:

locating a relatively narrow vertical histogram box centered horizontally substantially at the located crossing time;

accumulating histogram data corresponding to scans of the communications signal;

calculating the mean of the histogram data; and

designating the vertical location corresponding to the mean of the histogram data as the crossing level.

7. The method of claim 1 wherein the step of locating the crossing time further comprises the step of placing the horizontal histogram box having a vertical extent from just below the upper level to just above the lower level.

8. The method of claim 7, wherein:

the step of locating the crossing time further comprises the steps of;

placing the horizontal histogram box;

accumulating horizontal histogram data corresponding to scans of the communications signal;

calculating the mean and standard deviation of the horizontal histogram data;

the step of locating the crossing level comprises the steps of;

placing the vertical histogram box, having a width corresponding to the standard deviation of the horizontal histogram box, and a vertical extent from just below the upper level to just above the lower level, centered horizontally around the horizontal location corresponding to the mean of the horizontal histogram data;

accumulating vertical histogram data corresponding to scans of the communications signal;

calculating the mean and standard deviation of the vertical histogram data;

designating the crossing level as the vertical location corresponding to the mean of the vertical histogram data; and

the method further comprises the steps of;

determining the precision of the location of the crossing level;

if the precision of the crossing level is not within a predetermined precision;

setting the height of the horizontal histogram box to the standard deviation of the vertical histogram data; and

repeating the steps of locating the crossing time and locating the crossing level.

9. The method of claim 7, wherein the eye diagram further includes a symbol time, and:

the step of locating the upper level comprises the steps of;

locating a vertical histogram box at a vertical position within respective minimum and maximum limits of the upper level and at a horizontal position in the neighborhood of the symbol time;

accumulating upper level histogram data corresponding to scans of the communications signal;

calculating the mean and standard deviation of the histogram data; and

designating the vertical location corresponding to the mean as the upper level (vTop); and

the step of locating the lower level comprises the steps of;

locating a vertical histogram box at a vertical position within respective minimum and maximum limits of the lower level and at a horizontal position in the neighborhood of the symbol time;

accumulating lower level histogram data corresponding to scans of the communications signal;

calculating the mean and standard deviation of the histogram data; and

designating the vertical location corresponding to the mean as the lower level (vBase); and

the step of locating the crossing time further comprises the steps of;

placing the horizontal histogram box having a vertical extent from vTop−

6σ

(vTop) to vBase+6σ

(vBase), where 6σ

(vTop) is equal to six times the standard deviation of the upper level histogram data and 6σ

(vBase) is equal to six times the standard deviation of the lower level histogram data.