Apparatus for and method of cable diagnostics utilizing time domain reflectometry

• US 20060181283A1
• Filed: 02/13/2006
• Published: 08/17/2006
• Est. Priority Date: 02/14/2005
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Sommer, Naftali, Wajcer, Daniel, Semel, Nohik
• Granted Patent: US 7,245,129 B2
• Time in Patent Office: Days
• US Class Current: 324/539
• CPC Class Codes: G01R 31/11 using pulse reflection methods
• CPC Class Codes: H04B 3/46 Monitoring; Testing

Abstract

A novel mechanism for performing high accuracy cable diagnostics. The mechanism utilizes time domain reflectometry (TDR) to detect and identify cable faults, perform estimations of cable length, identify cable topology, identify load and irregular impedance on metallic paired cable, such as twisted pair and coaxial cables. The TDR mechanism transmits pulses whose shapes are programmable and analyzes the signal reflections. The shapes of the pulses transmitted can be optimized in accordance with the channel characteristics. Further, the TDR mechanism is adapted to operative in the presence of high pass filters in the channel.

Claims

1. A method of performing diagnostics on a metallic paired cable for use in a communications transceiver, said method comprising the steps of:

generating and transmitting a pulse from one end of said cable;

receiving a reflected signal and generating a sequence of samples therefrom;

detecting and measuring the amplitude of positive and negative peaks present in said reflected signal; and

determining diagnostic information about said cable based on the location and amplitude of said positive and negative peaks.

2. The method according to claim 1, wherein the width of said pulse is programmable.

3. The method according to claim 1, wherein the width of said pulse is one symbol wide for better diagnostic accuracy with shorter lengths of cable.

4. The method according to claim 1, wherein the width of said pulse is five symbols wide for better diagnostic accuracy with longer lengths of cable.

5. The method according to claim 1, wherein a peak is identified only if both its positive and negative portions are detected.

6. The method according to claim 1, wherein said positive peak is declared for a sample if the absolute value of the sample exceeds a low threshold, the sample is positive, the sample is larger than a previous number of samples and the sample is larger than a number of subsequent samples.

7. The method according to claim 1, wherein said negative peak is declared for a sample if the absolute value of the sample exceeds a low threshold, the sample is negative, the sample is smaller than a previous number of samples and the sample is smaller than a number of subsequent samples.

8. The method according to claim 1, wherein said step of detecting of peaks comprises the step of declaring an unmatched peak if a sufficient number of samples following a first peak, a second peak having a sign opposite that of said first peak and smaller absolute value is found and ignored.

9. The method according to claim 1, wherein said step of detecting of peaks comprises the step of declaring a matched peak if following a first peak, a second peak having a sign opposite that of said first peak and smaller absolute value is found and ignored.

10. The method according to claim 1, further comprising the step of declaring an open or shorted cable if a peak is identified that exceeds a high threshold.

11. The method according to claim 1, further comprising the step of ignoring peaks having a sign opposite that of a previously identified peak.

12. The method according to claim 1, wherein said step of determining comprises generating cable length as a function of peak location and amplitude information.

13. The method according to claim 1, wherein said step of determining comprises the step of locating one or more impedance mismatches existing along said cable.

14. The method according to claim 1, further comprising the step of performing generating, receiving and detecting several times and averaging corresponding samples.

15. The method according to claim 1, wherein the step of generating comprises the step of generating a plurality of pulses, each having different lengths.

16. An apparatus for performing cable diagnostics on a metallic paired cable for used in a communications transceiver, comprising:

a pulse generator coupled to said channel, said pulse generator operative to transmit a pulse onto said cable;

a peak detector coupled to said cable and operative to detect and measure the amplitude of positive and negative peaks present in a reflected signal;

a memory coupled to said peak detector for storing peak location and amplitude information; and

means for determining diagnostic information about said cable based on the location and amplitude of said positive and negative peaks.

17. An apparatus for performing cable diagnostics on a metallic paired cable for used in a communications transceiver, comprising:

means for generating and transmitting a pulse from one end of said cable;

means for receiving a reflected signal and generating a sequence of samples therefrom;

means for detecting and measuring the amplitude of positive and negative peaks present in said reflected signal; and

means for determining diagnostic information about said cable based on the location and amplitude of said positive and negative peaks.

18. A communications transceiver, comprising:

a transmitter;

a receiver;

a diagnostic module for performing cable diagnostics on a metallic paired cable coupled to said transceiver, said diagnostic module comprising;

a pulse generator coupled to said channel, said pulse generator operative to transmit a pulse onto said cable;

a peak detector coupled to said cable and operative to detect and measure the amplitude of positive and negative peaks present in a reflected signal;

a memory coupled to said peak detector for storing peak location and amplitude information; and

means for determining diagnostic information about said cable based on the location and amplitude of said positive and negative peaks.

19. A method of performing diagnostics on a metallic paired cable for use in a communications transceiver having an active link partner, said method comprising the steps of:

generating echo canceller coefficients;

detecting and measuring the amplitude of positive and negative peaks present in said echo canceller coefficients; and

determining diagnostic information about said cable based on the location and amplitude of said positive and negative peaks.