Method of time stamping a waveform edge of an input signal

• US 6,549,859 B1
• Filed: 09/05/2000
• Issued: 04/15/2003
• Est. Priority Date: 09/14/1999
• Status: Expired due to Fees

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Ward, Benjamin A.
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): West, Jeffrey R
• Application Number:
  US09/654,665
• Time in Patent Office: 952 Days
• Field of Search: 702/66, 702/67, 702/69-71, 702/72, 702/73, 702/74, 702/79, 702/107, 702/108, 702/117, 702/118, 702/120, 702/121, 702/124-126, 702/176-178, 702/183, 702/186, 702/187, 702/189, 702/193, 327/7, 327/9, 327/141, 327/263, 324/76.12, 324/76.13, 324/76.19
• US Class Current: 702/66
• CPC Class Codes: G01R 13/0245 for inserting reference markers
• CPC Class Codes: G01R 13/0272 for sampling
• CPC Class Codes: G01R 13/30 Circuits for inserting reference markers, e.g. for timing, for calibrating, for frequency marking
• CPC Class Codes: G01R 13/305 for time marking
• CPC Class Codes: G01R 13/345 for displaying sampled signals by using digital processors by intermediate A.D. and D.A. convertors (control circuits for CRT indicators)
• CPC Class Codes: G01R 19/175 Indicating the instants of passage of current or voltage through a given value, e.g. passage through zero

Abstract

The time stamping method for an input signal generates time marked digital data values as a reference edge and defines at least a first time stamp in the reference edge. Digital data samples of the input signal are acquired to create a waveform record of the input signal. The digital data samples of a waveform record edge are compared to time equivalent digital data values of the reference edge to generate a error value representative of the difference between the waveform record edge and the reference edge. A time offset value is generated from the error value to vary the time location of the reference edge and the comparison and time offset generating steps are repeated to minimize the error value. The time offset value at the minimum error value is combined with a time location of nearest digital data sample of the waveform record edge to generate a waveform record edge time stamp.

Claims

1. A method of time stamping an edge of an input signal comprising the steps of:

a) generating a reference edge having timed marked digital data values;

b) defining at least a first time stamp in the reference edge;

c) acquiring digital data samples of the input signal to create a waveform record of the input signal;

d) comparing the digital data samples of a waveform record edge to time equivalent digital data values of the reference edge to generate amplitude error vectors representative of the difference between the digital data samples of the waveform record edge and the time equivalent digital data values of the reference edge;

e) summing the amplitude error vectors to generate a total error value;

f) generating a time offset value from the total error value to vary the time location of the reference edge;

g) repeating steps (d) through (f) to minimize the total error value;

h) combining the time offset value at the minimum total error value with a time location of nearest digital data sample of the waveform record edge to generate a waveform record edge time stamp.

2. The method of time stamping an edge in an input signal as recited in claim 1 wherein the reference edge generating step further comprises the step of over-sampling and averaging digital data samples of the input signal.

3. The method of time stamping an edge in an input signal as recited in claim 1 wherein the reference edge generating step further comprises the step of storing time marked digital data values representative of the reference edge.

4. The method of time stamping an edge in an input signal as recited in claim 1 wherein the reference edge generating step further comprises the steps of:

a) storing an algorithm representative of the reference edge; and

b) generating time marked digital data values using the reference edge algorithm.

5. The method of time stamping an edge in an input signal as recited in claim 1 wherein the reference edge generating step further comprises generating a rising reference edge.

6. The method of time stamping an edge in an input signal as recited in claim 1 wherein the reference edge generating step further comprises generating a falling reference edge.

7. The method of time stamping an edge in an input signal as recited in claim 1 wherein the reference edge generating step further comprises generating the digital data samples using equivalent time sampling and averaging.

8. The method of time stamping an edge in an input signal as recited in claim 1 wherein the step of defining the time stamp further comprises the step of determining a 50% point in the reference edge.

9. The method of time stamping an edge in an input signal as recited in claim 1 wherein the step of defining the time stamp further comprises the step of determining first and second time stamps in the reference edge for performing rise and fall time measurements.

10. The method of time stamping an edge in an input signal as recited in claim 9 wherein the first and second time stamp determining step further comprises the step of establishing a 10% point and a 90% point in the reference edge for the first and second time stamps for performing rise and fall time measurements on the waveform record edge.

11. The method of time stamping an edge in an input signal as recited in claim 9 wherein the waveform record edge contains noise artifacts and the first and second time stamp determining step further comprises the step of establishing a 20% point and a 80% point in the reference edge for the first and second time stamps for performing rise and fall time measurements on the noisy waveform record edge.

12. The method of time stamping an edge in an input signal as recited in claim 1 wherein the time offset value generating step further comprises the steps of:

a) applying the total error value as an index value into a table of summed error values versus delta offset values to retrieve a delta offset value;

b) adding the delta offset value to a current time offset value to generate a new time offset value;

c) applying the new time offset value to the digital data values of the reference edge to vary the time locations of the digital data values of the reference edge; and

d) repeating steps (a) through (c) for each new total error value for a predetermined number of iterations.

13. The method of time stamping an edge in an input signal as recited in claim 12 wherein the indexing step further comprises the step of applying a scalar value to the error value.

14. The method of time stamping an edge in an input signal as recited in claim 1 wherein the time offset value generating step further comprises the steps of:

a) applying the total error value as an index value into a table of summed error values versus delta offset values to retrieve a delta offset value;

b) adding the delta offset value to a current time offset value to generate a new time offset value;

c) applying the new time offset value to the digital data values of the reference edge to vary the time locations of the digital data values of the reference edge; and

d) repeating step (a) through (c) for each new total error value until the delta offset falls within a threshold region.

15. The method of time stamping an edge in an input signal as recited in claim 14 wherein the indexing step further comprises the step of applying a scalar value to the error value.