Tuning a testing apparatus for measuring skew

• US 10,162,002 B2
• Filed: 07/20/2015
• Issued: 12/25/2018
• Est. Priority Date: 07/20/2015
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Berge, Layne A., Fox, Benjamin A., Martin, Wesley D., Siljenberg, David W., Zettles, IV, George R.
• Primary Examiner(s): Kerveros, James C
• Application Number:
  US14/803,326
• Publication Number:
  US 20170023646A1
• Time in Patent Office: 1,254 Days
• Field of Search: 714700, 324533
• CPC Class Codes: G01R 31/31709 Jitter measurements; Jitter generators measuring jitter, noise figure or signal-to-noise ratio per se G01R29/26; analysis of tester signals G01R31/31901
• CPC Class Codes: G01R 31/31725 Timing aspects, e.g. clock distribution, skew, propagation delay for tester hardware G01R31/31937
• CPC Class Codes: G01R 31/31727 Clock circuits aspects, e.g. test clock circuit details, timing aspects for signal generation, circuits for testing clocks G01R31/31725 takes precedence; concerning scan test G01R31/318552, for tester hardware G01R31/31922

Abstract

Embodiments herein discuss tuning a testing apparatus to better match the input response of a target system in which a cable will be used. For example, conductors in the cable may have a different skew depending on the system in which they are used. The testing apparatus may be tuned using frequency information regarding the type of signals that will be driven on the cable when installed in the target system. In one embodiment, the testing apparatus uses the frequency information to configure a programmable clock source that can be used to shape a reference clock and control a driver to match the signals in the target system. Using the clock source to modify the reference clock results in the driver outputting a testing signal that better reflects the actual signals that will be transmitted on the cable in the target system.

Claims

1. A method comprising:

configuring a programmable clock source in a testing apparatus by selecting a configuration of the clock source from a plurality of pre-defined configurations of the clock source, wherein each configuration of the clock source corresponds to a respective frequency response of the testing apparatus different from frequency responses of other configurations of the clock source, and wherein each of the respective frequency responses represents a respective change of output power of the clock source as a function of frequency, and wherein each of the respective frequency responses of the plurality of pre-defined configurations includes frequency content used by a respective target computing system in a plurality of target computing systems, wherein the frequency content includes a range of frequencies used by the respective target computing system during operation;

processing a reference clock signal using the configured clock source to generate a modified clock signal that is uniquely generated by the selected pre-defined configuration of the clock source;

driving a testing signal based on the modified clock signal onto a plurality of conductors, wherein the plurality of conductors are configured to be used in one of the plurality of target computing systems; and

measuring skew between the plurality of conductors in response to driving the testing signal.

2. The method of claim 1, wherein the plurality of conductors are disposed in a cable.

3. The method of claim 1, further comprising:

receiving a testing cycle refresh rate, wherein the testing signal is derived based on the testing cycle refresh rate and the modified clock signal.

4. The method of claim 1, wherein the testing apparatus comprises a time domain reflectometer (TDR).

5. The method of claim 1, further comprising:

iteratively selecting new configurations of the clock source until a comparison between a first skew measurement calculated using a current configuration of the clock source and a second skew measurement calculated using a previous configuration of the clock source satisfy a threshold; and

upon determining the threshold is satisfied, outputting for display one of;

the first skew measurement, the second skew measurement, and a combination of the first and second skew measurements.

6. A testing apparatus, comprising:

a clock adjustor configured to;

configure a programmable clock source by selecting a configuration of the clock source from a plurality of pre-defined configurations of the clock source, wherein each configuration of the clock source corresponds to a respective frequency response of the testing apparatus different from frequency responses of other configurations of the clock source, and wherein each of the respective frequency responses represents a respective change of output power of the clock source as a function of frequency, and wherein each of the respective frequency responses of the plurality of pre-defined configurations includes frequency content used by a respective target computing system of a plurality of target computing systems, wherein the frequency content includes a range of frequencies used by the respective target computing system during operation, and

process a reference clock signal using the configured clock source to generate a modified clock signal that is uniquely generated by the selected pre-defined configuration of the clock source;

a driver configured to drive a testing signal based on the modified clock signal onto a plurality of conductors, wherein the plurality of conductors are configured to be used in one of the plurality of target computing systems; and

a skew calculator configured to measure skew between the plurality of conductors in response to driving the testing signal.

7. The testing apparatus of claim 6, wherein the driver is configured to set a testing cycle refresh rate of the testing signal based on upon receiving the testing cycle refresh rate from user input.

8. The testing apparatus of claim 6, further comprising a TDR.

9. The testing apparatus of claim 8, further comprising a pluggable TDR head in the TDR, wherein the driver and clock adjustor are disposed in the TDR head.

10. The testing apparatus of claim 6, wherein the clock adjustor is configured to iteratively select new configurations of the clock source until a comparison between a first skew measurement calculated using a current configuration of the clock source and a second skew measurement calculated using a previous configuration of the clock source satisfy a threshold,

wherein the skew calculator is configured to output for display one of:

the first skew measurement, the second skew measurement, and a combination of the first and second skew measurements upon determining the threshold is satisfied.

11. A computer program product for testing a plurality of conductors, the computer program product comprising:

a computer-readable storage medium having computer-readable program code embodied therewith, the computer-readable program code executable by one or more computer processors to;

configure a programmable clock source in a testing apparatus by selecting a configuration of the clock source from a plurality of pre-defined configurations of the clock source, wherein each configuration of the clock source corresponds to a respective frequency response of the testing apparatus different from frequency responses of other configurations of the clock source, and wherein each of the respective frequency responses represents a respective change of output power of the clock source as a function of frequency, and wherein each of the respective frequency responses of the plurality of pre-defined configurations includes frequency content used by a respective target computing system of a plurality of target computing systems wherein the frequency content includes a range of frequencies used by the respective target computing system during operation;

process a reference clock signal using the configured clock source to generate a modified clock signal that is uniquely generated by the selected pre-defined configuration of the clock source;

drive a testing signal based on the modified clock signal onto a plurality of conductors, wherein the plurality of conductors are configured to be used in one of the plurality of target computing systems; and

measure skew associated with the conductors in response to driving the testing signal.

12. The computer program product of claim 11, wherein the plurality of conductors are disposed in a cable.

13. The computer program product of claim 11, wherein the computer-readable program code is further executable to:

receive a testing cycle refresh rate, wherein the testing signal is derived based on the testing cycle refresh rate and the modified clock signal.

14. The computer program product of claim 11, wherein the testing apparatus comprises a TDR.