Signal analysis system and calibration method for multiple signal probes

• US 20080048673A1
• Filed: 08/23/2006
• Published: 02/28/2008
• Est. Priority Date: 08/23/2006
• Status: Active Grant

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Tan, Kan, Pickerd, John J.
• Granted Patent: US 7,414,411 B2
• Time in Patent Office: Days
• US Class Current: 324/601
• CPC Class Codes: G01R 1/06772 High frequency probes
• CPC Class Codes: G01R 1/06788 Hand-held or hand-manipulated probes, e.g. for oscilloscopes or for portable test instruments end pieces terminating in a probe H01R11/18
• CPC Class Codes: G01R 27/28 Measuring attenuation, gain, phase shift or derived characteristics of electric four pole networks, i.e. two-port networks; Measuring transient response in line transmission systems H04B3/46
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

Abstract

A method and apparatus adapted to calibrate signal path of a signal analysis system such that loading effects of additional probes are substantially removed from the measurement. A signal under test from a device under test is coupled to a test probe and used with selectable impedance loads in the test probe to acquires sets of samples for characterizing transfer parameters of the device under test and compute open circuit voltages at the test probe. Other probes are coupled to the device under test and a set of measurement samples are acquired via the test probe. An equalization filter in either the frequency or time domain is computed from the open circuit voltage and measurement samples for reducing signal errors attributable to the measurement loading of the device under test by the test probe and other probes.

Claims

1. A method of calibrating a signal path of a signal analysis system comprising the steps of:

comprising the steps;

connecting a first probe P₁ to a device under test and acquiring sets of samples in the time domain of the signal under test from the device under test via a first probe signal path SP₁ including a plurality of selectable impedance loads with the first probe signal path SP₁ for each set of samples having a selected impedance load of the plurality of selectable impedance loads;

converting the sets of samples in the time domain of the signal under test to spectral domain representations;

characterizing transfer parameters of the device under test within a spectral domain from the spectral domain representations;

calculating an open circuit voltage (v_open^P1(f)) of the device under test in the spectral domain using the characterizing transfer parameters of the device under test;

connecting a second probe P₂ to the device under test and acquiring a set of measurement samples in the time domain of the signal under test from the device under test via the first probe P₁ of the first probe signal path SP₁ including one of the selected impedance loads;

converting the plurality of measurement samples in the time domain to a spectral domain representation (v_meas^P1(f));

computing an equalization filter adapted to compensate for loading of the device under test caused by the first and second probes, P₁ and P₂, using the spectral domain open circuit voltage (v_open^P1(f)) and measurement samples (V_meas^P1(f));

acquiring at least an additional set of samples of the signal under test from the device under test in the time domain via the first probe P₁ of the first probe signal path SP₁ including the selectable impedance load of the set of samples used for acquiring the measurement samples;

converting the additional set of samples of the signal under test from the time domain to a spectral domain representation; and

processing the spectral domain representation of the additional set of samples using the computed equalization filter to effect thereby an open circuit voltage (v_open^P1(f)) having a reduction in signal error attributable to the measurement loading of the device under test caused by the first and second probes, P₁ and P₂.

2. The method of calibrating a signal path of a signal analysis system as recited in claim 1 wherein the connecting of the first probe P₁ step further comprise the step of synchronizing the signal under test to a trigger signal.

3. A method of calibrating a signal path of a signal analysis system comprising the steps of:

connecting a first probe P₁ to a device under test and acquiring sets of samples in the time domain of the signal under test from the device under test via a first probe signal path SP₁ including a plurality of selectable impedance loads with the first probe signal path SP₁ for each set of samples having a selected impedance load of the plurality of selectable impedance loads;

converting the sets of samples in the time domain of the signal under test to spectral domain representations;

characterizing transfer parameters of the device under test within a spectral domain from the spectral domain representations;

calculating an open circuit voltage (v_open^P1(f)) of the device under test in the spectral domain using the characterizing transfer parameters of the device under test;

connecting a second probe P₂ to the device under test and acquiring a set of measurement samples in the time domain of the signal under test from the device under test via the first probe P₁ of the first probe signal path SP₁ including one of the selected impedance loads;

converting the plurality of measurement samples in the time domain to a spectral domain representation (V_meas^P1(f));

computing an equalization filter adapted to compensate for loading of the device under test caused by the first and second probes, P₁ and P₂, using the spectral domain open circuit voltage (v_open^P1(f)) and measurement samples (v_meas^P1(f));

converting the computed equalization filter from the frequency domain to a time domain equalization filter;

acquiring at least an additional set of samples of the signal under test from the device under test in the time domain via the first probe P₁ of the first probe signal path SP₁ including the selectable impedance load of the set of samples used for acquiring the measurement samples; and

processing the of the additional set of samples of the signal under test in the time domain using the time domain equalization filter to effect thereby an open circuit voltage (V_open^P1(t)) having a reduction in signal error attributable to the measurement loading of the device under test caused by the first and second probes, P₁ and P₂.

4. The method of calibrating a signal path of a signal analysis system as recited in claim 3 wherein the connecting of the first probe P₁ step further comprise the step of synchronizing the signal under test to a trigger signal.

5. A method of calibrating a signal path of a signal analysis system comprising the steps of:

comprising the steps;

connecting a first probe P₁ to a device under test and acquiring a first set of samples in the time domain of the signal under test from the device under test via a first probe signal path SP₁;

acquiring at least a second set of samples in the time domain of a signal under test from a device under test via the first probe P₁ of the first probe signal path SP₁ including at least a first selectable impedance load coupled to the first probe;

converting the first and second sets of samples of the signal under test in the time domain to spectral domain representations;

characterizing transfer parameters of the device under test within a spectral domain from the spectral domain representations for each of the first and second sets of samples;

calculating an open circuit voltage (v_open^P1(f)) of the device under test in the spectral domain using the characterizing transfer parameters of the device under test;

connecting a second probe P₂ to the device under test and acquiring a set of measurement samples in the time domain of the signal under test from the device under test via the first probe P₁ of the first probe signal path SP₁ including one of the probe or the probe and selected impedance load;

converting the plurality of measurement samples in the time domain to a spectral domain representation (v_meas^P1(f));

computing an equalization filter adapted to compensate for loading of the device under test caused by the first and second probes, P₁ and P₂, using the spectral domain open circuit voltage (v_open^P1(f)) and measurement samples (v_meas^P1(f));

acquiring at least an additional set of samples of the signal under test from the device under test in the time domain via the first probe P₁ of the first probe signal path SP₁ including the selected probe or the probe and selected impedance load used for acquiring the measurement samples;

converting the additional set of samples of the signal under test from the time domain to a spectral domain representation; and

processing the spectral domain representation of the additional set of samples using the computed equalization filter to effect thereby an open circuit voltage (v_open^P1(f)) having a reduction in signal error attributable to the measurement loading of the device under test caused by the first and second probes, P₁ and P₂.

6. The method of calibrating a signal path of a signal analysis system as recited in claim 5 wherein the connecting of the first probe P₁ step further comprise the step of synchronizing the signal under test to a trigger signal.

7. A method of calibrating a signal path of a signal analysis system comprising the steps of:

connecting a first probe P₁ to a device under test and acquiring a first set of samples in the time domain of the signal under test from the device under test via a first probe signal path SP₁;

acquiring at least a second set of samples in the time domain of a signal under test from a device under test via the first probe P₁ of the first probe signal path SP₁ including at least a first selectable impedance load coupled to the first probe;

converting the first and second sets of samples of the signal under test in the time domain to spectral domain representations;

characterizing transfer parameters of the device under test within a spectral domain from the spectral domain representations for each of the first and second sets of samples;

calculating an open circuit voltage (v_open^P1(f)) of the device under test in the spectral domain using the characterizing transfer parameters of the device under test;

connecting a second probe P₂ to the device under test and acquiring a set of measurement samples in the time domain of the signal under test from the device under test via the first probe P₁ of the first probe signal path SP₁ including one of the probe or the probe and selected impedance load;

converting the plurality of measurement samples in the time domain to a spectral domain representation (v_meas^P1(f));

computing an equalization filter adapted to compensate for loading of the device under test caused by the first and second probes, P₁ and P₂, using the spectral domain open circuit voltage (v_open^P1(f)) and measurement samples (v_meas^P1(f));

converting the computed equalization filter from the frequency domain to a time domain equalization filter;

acquiring at least an additional set of samples of the signal under test from the device under test in the time domain via the first probe P₁ of the first probe signal path SP₁ including the selected probe or the probe and selected impedance load used for acquiring the measurement samples; and

processing the of the additional set of samples of the signal under test in the time domain using the time domain equalization filter to effect thereby an open circuit voltage (V_open^P1(t)) having a reduction in signal error attributable to the measurement loading of the device under test caused by the first and second probes, P₁ and P₂.

8. The method of calibrating a signal path of a signal analysis system as recited in claim 7 wherein the connecting of the first probe P₁ step further comprise the step of synchronizing the signal under test to a trigger signal.

9. A method of calibrating a signal path of a signal analysis system comprising the steps of:

comprising the steps;

providing transfer parameters for a device under test;

connecting a first probe P₁ to the device under test and acquiring a set of samples in the time domain of the signal under test from the device under test via a first probe signal path SP₁;

converting the set of samples in the time domain of the signal under test to spectral domain representations;

computing a signal under test voltage for the device under test using the spectral domain representation of the plurality of samples;

computing open circuit voltages (v_open^P1(f)) within a spectral domain from the transfer parameters of the device under test and the input voltage for the device under test;

connecting a second probe P₂ to the device under test and acquiring a set of measurement samples in the time domain of the signal under test from the device under test via the first prob P₁ of the first probe signal path SP₁ including one of the selected impedance loads;

converting the plurality of measurement samples in the time domain to a spectral domain representation (v_meas^P1(f));

computing an equalization filter adapted to compensate for loading of the device under test caused by the first and second probes, P₁ and P₂ using the spectral domain open circuit voltage (v_open^P1(f)) and measurement samples (v_meas^P1(f));

acquiring at least an additional set of samples of the signal under test from the device under test in the time domain via the first probe P₁ of the first probe signal path SP₁ including the selectable impedance load of the set of samples used for acquiring the measurement samples;

converting the additional set of samples of the signal under test from the time domain to a spectral domain representation; and

processing the spectral domain representation of the additional set of samples using the computed equalization filter to effect thereby an open circuit voltage (v_open^P1(f)) having a reduction in signal error attributable to the measurement loading of the device under test caused by the first and second probes, P₁ and P₂.

10. The method of calibrating a signal path of a signal analysis system as recited in claim 9 wherein the connecting of the first probe P₁ step further comprise the step of synchronizing the signal under test to a trigger signal.

11. A method of calibrating a signal path of a signal analysis system comprising the steps of:

providing transfer parameters for a device under test;

connecting a first probe P₁ to the device under test and acquiring a set of samples in the time domain of the signal under test from the device under test via a first probe signal path SP₁;

converting the set of samples in the time domain of the signal under test to spectral domain representations;

computing a signal under test voltage for the device under test using the spectral domain representation of the plurality of samples;

computing open circuit voltages (v_open^P1(f)) within a spectral domain from the transfer parameters of the device under test and the input voltage for the device under test;

connecting a second probe P₂ to the device under test and acquiring a set of measurement samples in the time domain of the signal under test from the device under test via the first probe P₁ of the first probe signal path SP₁ including one of the selected impedance loads;

converting the plurality of measurement samples in the time domain to a spectral domain representation (v_meas^P1(f));

computing an equalization filter adapted to compensate for loading of the device under test caused by the first and second probes, P₁ and P₂, using the spectral domain open circuit voltage (v_open^P1(f)) and measurement samples (v_meas^P1(f));

converting the computed equalization filter from the frequency domain to a time domain equalization filter;

acquiring at least an additional set of samples of the signal under test from the device under test in the time domain via the first probe, P₁ of the first probe signal path SP₁ including the selectable impedance load of the set of samples used for acquiring the measurement samples; and

processing the of the additional set of samples of the signal under test in the time domain using the time domain equalization filter to effect thereby an open circuit voltage (V_open^P1(t)) having a reduction in signal error attributable to the measurement loading of the device under test caused by the first and second probes, P₁ and P₂.

12. The method of calibrating a signal path of a signal analysis system as recited in claim 11 wherein the connecting of the first probe P₁ step further comprise the step of synchronizing the signal under test to a trigger signal.

13. A method of calibrating a plurality of signal paths of a signal analysis system comprising the steps:

a) connecting a probe P₁ of a series of probes P₁, P₂, . . . P_n to a device under test and acquiring sets of samples in the time domain of one of a plurality of signals under test from a device under test via a probe signal path SP₁ of a series of signal paths SP₁, SP₂, . . . SP_n corresponding to each of the series of probes P₁, P₂, . . . P_n with each probe signal path for each set of samples having a selected impedance load of a plurality of selectable impedance loads;

b) converting the sets of samples in the time domain of the signal under test to a spectral domain representations;

c) characterizing transfer parameters of the device under test within a spectral domain from the spectral domain representations;

d) calculating an open circuit voltage {circumflex over (v)}_open^Pi(f) i=1, 2, . . . . n of the device under test in the spectral domain using the characterizing transfer parameters of the device under test;

e) disconnecting the probe from the device under test and connecting a next probe of the series of probes P₁, P₂, . . . P_n to the device under test;

f) acquiring sets of samples in the time domain of another of the plurality of signals under test from the device under test via the another of the probe signal paths SP₁, SP₂, . . . SP_n corresponding to next probe of the series of probes P₁, P₂, . . . P_n with the probe signal path for each set of samples for next probe of the series of probes P₁, P₂, . . . P_n having a selected impedance load of a plurality of selectable impedance loads;

g) repeating steps b), c), and d) for the next probe of the series of probes P₁, P₂, . . . P_n;

h) repeating steps e), f) and g) for each of the remaining probes of the series of probes P₁, P₂, . . . P_n;

i) connecting all of the probe of the series of probes P₁, P₂, . . . P_n to the device under test;

j) acquiring a sets of measurement samples in the time domain of the plurality of signals under test from the device under test via each of the series of probes P₁, P₂, . . . P_n of the probe signal paths SP₁, SP₂, . . . SP_n including one of the selectable impedance loads of the respective probe signal paths SP₁, SP₂, . . . SP_n;

k) converting the sets of measurement samples in the time domain of the plurality of signals under test from each of the probe signal paths SP₁, SP₂, . . . SP_n to a spectral domain representations {circumflex over (v)}_meas^Pi(f) i=1, 2 . . . n;

l) computing an equalization filter for each probe of the series of probes P₁, P₂, . . . P_n adapted to compensate for loading of the device under test caused by the series of probes P₁, P₂, . . . P_n using the spectral domain open circuit voltage {circumflex over (v)}_open^Pi(f) i=1, 2, . . . n and measurement samples {circumflex over (v)}_meas^Pi(f) i=1, 2 . . . . n for each of the series of probes P₁, P₂, . . . P_n;

m) acquiring at least an additional set of samples for each of the plurality of signals under test from the device under test in the time domain via the series of probes P₁, P₂, . . . P_n of the probe signal paths SP₁, SP₂, . . . SP_n including the respective selectable impedance loads used for acquiring the measurement samples from of the series of probes P₁, P₂, . . . P_n of the probe signal paths SP₁, SP₂, . . . SP_n;

n) converting the additional sets of samples of the plurality of signals under test from the time domain to a spectral domain representations from each of the series of probes P₁, P₂, . . . P_n of the probe signal paths SP₁, SP₂, . . . SP_n; and

o) processing the spectral domain representation of the additional sets of samples using the respective computed equalization filter for each of the series of probes P₁, P₂, . . . P_n to effect thereby an open circuit voltage {circumflex over (v)}_open^Pi(f) i=1, 2, . . . n having a reduction in signal error attributable to the measurement loading of the device under test caused by the series of probes P₁, P₂, . . . P_n.

14. The method of calibrating a signal path of a signal analysis system as recited in claim 13 wherein the connecting of the probe P₁ step further comprise the step of synchronizing the signals under test to a trigger signal.

15. A method of calibrating a plurality of signal paths of a signal analysis system comprising the steps:

a) connecting a probe P₁ of a series of probes P₁, P₂, . . . P_n to a device under test and acquiring sets of samples in the time domain of one of a plurality of signals under test from a device under test via a probe signal path SP₁ of a series of signal paths SP₁, SP₂, . . . SP_n corresponding to each of the series of probes P₁, P₂, . . . P_n with each probe signal path for each set of samples having a selected impedance load of a plurality of selectable impedance loads;

b) converting the sets of samples in the time domain of the signal under test to a spectral domain representations;

c) characterizing transfer parameters of the device under test within a spectral domain from the spectral domain representations;

d) calculating an open circuit voltage {circumflex over (v)}_open^Pi(f) i=1, 2 . . . . n of the device under test in the spectral domain using the characterizing transfer parameters of the device under test;

e) disconnecting the probe from the device under test and connecting a next probe of the series of probes P₁, P₂, . . . P_n to the device under test;

f) acquiring sets of samples in the time domain of another of the plurality of signals under test from the device under test via the another of the probe signal paths SP₁, SP₂, . . . SP_n corresponding to next probe of the series of probes P₁, P₂, . . . P_n with the probe signal path for each set of samples for next probe of the series of probes P₁, P₂, . . . P_n having a selected impedance load of a plurality of selectable impedance loads;

g) repeating steps b), c), and d) for the next probe of the series of probes P₁, P₂, . . . P_n;

h) repeating steps e), f) and g) for each of the remaining probes of the series of probes P₁, P₂, . . . P_n;

i) connecting all of the probe of the series of probes P₁, P₂, . . . P_n to the device under test;

j) acquiring a sets of measurement samples in the time domain of the plurality of signals under test from the device under test via each of the series of probes P₁, P₂, . . . P_n of the probe signal paths SP₁, SP₂, . . . SP_n, including one of the selectable impedance loads of the respective probe signal paths SP₁, SP₂, . . . SP_n;

k) converting the sets of measurement samples in the time domain of the plurality of signals under test from each of the probe signal paths SP₁, SP₂, . . . SP_n to a spectral domain representations {circumflex over (v)}_meas^Pi(f) i=1, 2, . . . n;

l) computing an equalization filter for each probe of the series of probes P₁, P₂, . . . P_n adapted to compensate for loading of the device under test caused by the series of probes P₁, P₂, . . . P_n using the spectral domain open circuit voltage {circumflex over (v)}_open^Pi(f) i=1, 2, . . . n and measurement samples {circumflex over (v)}_meas^Pi(f) i=1, 2, . . . n for each of the series of probes P₁, P₂, . . . P_n;

m) converting each of the equalization filters for the series of probes P₁, P₂, . . . P_n to time domain equalization filters;

n) acquiring at least an additional set of samples for each of the plurality of signals under test from the device under test in the time domain via the series of probes P₁, P₂, . . . P_n of the probe signal paths SP₁, SP₂, . . . SP_n including the respective selectable impedance loads used for acquiring the measurement samples from of the series of probes P₁, P₂, . . . P_n of the probe signal paths SP₁, SP₂, . . . SP_n; and

o) processing the additional sets of samples using the respective computed time domain equalization filter for each of the series of probes P₁, P₂, . . . P_n to effect thereby an open circuit voltage {circumflex over (v)}_open^Pi(f) i=1, 2, . . . n having a reduction in signal error attributable to the measurement loading of the device under test caused by the series of probes P₁, P₂, . . . P_n.

16. The method of calibrating a signal path of a signal analysis system as recited in claim 15 wherein the connecting of the probe P₁ step further comprise the step of synchronizing the signals under test to a trigger signal.