Period determination of a periodic NRZ signal

• US 7,379,830 B2
• Filed: 05/24/2005
• Issued: 05/27/2008
• Est. Priority Date: 05/25/2004
• Status: Expired due to Fees

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Onu, Dan
• Primary Examiner(s): Barlow; John
• Assistant Examiner(s): Le; Toan M.
• Application Number:
  US11/137,176
• Publication Number:
  US 20050273285A1
• Time in Patent Office: 1,099 Days
• Field of Search: 702/66, 702/67, 702/57, 702/71, 702/73, 702/108, 702/127, 702/189, 324/121.R, 345/440.1
• US Class Current: 702/67
• CPC Class Codes: G11B 20/14 using self-clocking codes
• CPC Class Codes: G11B 20/1403 characterised by the use of two levels

Abstract

A method and apparatus for determining the period T_p of a signal representing a digitally modulated waveform using NRZ coding with a discrete/integer number of a clock periods between signal transitions, where a periodic sequence of logic “1s” and logic “0s” is transmitted. The method samples an input periodic signal, constructs an estimate of the autocorrelation sequence r_k of the sequence of samples, constructs a sequence of peaks p_k, and computes the period T_p to be the time between the first p_k sample (k=0), and the time location of the maximum value of p_k based on the known T_s spacing of the p_k sequence samples.

Claims

1. An oscilloscope having a program determining the period of a periodic non-return-to-zero signal, comprising:

an acquisition circuit sampling said periodic no-return-to-zero signal at a predetermined sample rate having a predetermined sample interval;

a waveform memory for storing said samples;

a memory for storing said program;

a processor constructing an estimate of an autocorrelation sequence of said samples;

said processor constructing a sequence of peaks based upon said autocorrelation estimate;

said processor computing said period of said periodic non-return-to-zero signal as the interval between a time location of a first peak of said sequence of peaks and a time location of a peak having a maximum value with respect to other peaks based upon said predetermined sample interval; and

a display screen;

wherein

at least one of said autocorrelation, said estimate, and said sequence of peaks is displayed on said display screen.

2. The oscilloscope of claim 1 wherein,

said sequence of samples is X(k)=X(T_k) where said predetermined sample interval is T_s, and T_k=n*Ts.

3. The oscilloscope of claim 2 wherein,

said processor constructs said estimate by computing

$r_k=\frac{1}{N}$

∑

i = 1 N ⁢

x i ⁢

x i + k ,

for k=0;

(N−

1), where x_i=0 for i<

0 or i>

N.

4. The oscilloscope of claim 3 wherein,

said processor constructs said sequence of peaks by constructing a sequence

$p_k=\frac{r_k-r_{k/2}}{r_0-r_{k/2}},$

wherein odd values of k the value of r_k/2 are estimated by averaging based on adjacent r_K samples.

5. The oscilloscope of claim 4 wherein,

said processor computes a period T_p as a time between a first p_k sample (k=0), and a time of a maximum value of p_k based upon said T_s spacing of said p_k sequence samples.

6. The oscilloscope of claim 5 wherein,

said processor constructs said sequence of peaks by constructing a sequence

$p_k=\frac{r_k-r_{k/2}}{r_0-r_{k/2}},$

wherein odd values of k the value of r_k/2 are estimated by averaging based on adjacent r_k samples.

7. The oscilloscope of claim 6 wherein,

said processor computes a period T_p as a time between a first P_k sample (k=0), and a time of a maximum value of p_k based upon said T_s spacing of said p_k sequence samples.

8. The oscilloscope of claim 5 wherein,

said processor constructs said sequence of peaks by constructing a sequence

$p_k=\frac{r_k-r_{k/2}}{r_0-r_{k/2}},$

wherein odd values of k the value of r_k/2 are estimated using interpolation.

9. The oscilloscope of claim 8 wherein,

said processor computes a period T_p as a time between a first p_k sample (k=0), and a time of a maximum value of p_k based upon said T_s spacing of said p_k sequence samples.

10. The oscilloscope of claim 2 wherein,

said processor constructs said estimate includes by computing a Fourier transform sequence X_k of x_k;

squaring magnitudes of values of X_k point-by-point to obtain a sequence of power spectral density S_k of x_k; and

computing an inverse Fourier Transform of S_k to obtain a sequence r_K.

11. The oscilloscope of claim 3 wherein,

said processor constructs said sequence of peaks by constructing a sequence

$p_k=\frac{r_k-r_{k/2}}{r_0-r_{k/2}},$

wherein odd values of k the value of r_k/2 are estimated using interpolation.

12. The oscilloscope of claim 11 wherein,

said processor computes a period T_p as a time between a first p_k sample (k=0), and a time of a maximum value of p_k based upon said T_s spacing of said p_k sequence samples.