Method and apparatus for in-circuit impedance measurement

• US 6,737,875 B2
• Filed: 12/17/2001
• Issued: 05/18/2004
• Est. Priority Date: 05/22/2000
• Status: Expired due to Fees

• Current Assignee: Signus Incorporated
• Original Assignee: Damerco Incorporated
• Inventors: Davis, Larry J., Cox, Kenneth M.
• Primary Examiner(s): Oda, Christine
• Assistant Examiner(s): Hamdan, Wasseem H.
• Application Number:
  US10/024,587
• Publication Number:
  US 20020153901A1
• Time in Patent Office: 883 Days
• Field of Search: 324/713, 324/548, 324/549, 324/704, 324/715, 324/72.5, 324/545
• US Class Current: 324/713
• CPC Class Codes: G01R 1/06761 related to layers
• 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 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00
• CPC Class Codes: G01R 27/16 Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
• CPC Class Codes: G01R 31/27 Testing of devices without physical removal from the circuit of which they form part, e.g. compensating for effects surrounding elements testing printed circuit boards G01R31/2801
• CPC Class Codes: G01R 31/2813 Checking the presence, location, orientation or value, e.g. resistance, of components or conductors orientation of the DUT with respect to the test fixture G01R1/06705, G01R31/281
• CPC Class Codes: G01R 31/2843 In-circuit-testing

Abstract

A device and method for measuring an impedance between first and second nodes in an electrical circuit without removing components includes at least one current source to provide first and second currents or current signals of known values. First and second probes contact the respective first and second nodes to apply the first and second currents. A third common probe contacts the circuit at a common node that experiences the same current flow as between the first and second nodes. At least one voltage meter measures voltages corresponding to the first and second currents. A processor calculates the impedance based on the known values of the currents, and the measured values of the voltages.

Claims

1. A device configured to measure an impedance between first and second nodes of an electrical circuit, the device comprising:

a) at least one current source configured to provide first and second currents of known values;

b) first and second probes, connected to the at least one current source, and configured to contact the respective first and second nodes to apply the first and second currents to the first and second nodes;

c) a third common probe, connected to the at least one current source, configured to contact the circuit at a common node at a location that has an equal current flow with respect to the first and second nodes;

d) at least one voltage meter, configured to be connected to the first and second nodes, to measure voltages corresponding to the first and second currents; and

e) a processor, operatively coupled to the at least one current source and the at least one voltage meter, capable of calculating the unknown impedance based on the known values of the first and second current and the measured values of the voltages.

2. A device in accordance with claim 1, wherein the at least one current source is configured to provide different first and second current signals.

3. A device in accordance with claim 1, wherein the at least one current source is configured to provide different sinusoidal current signals.

4. A device in accordance with claim 1, wherein the processor is configured to isolate the voltages measured by the at least one voltage meter caused by the first and second currents.

5. A device in accordance with claim 1, wherein the at least one voltage meter is connected to the respective first and second probes, and is connected to the third common probe.

6. A device in accordance with claim 1, further comprising:

a) a fourth probe, connected to a first voltage meter, and configured to contact the first node;

b) a fifth probe, connected to a second voltage meter, and configured to contact the second node; and

c) a sixth common probe, connected to the first and second voltage meters, and configured to contact the circuit at the common node at the location that has an equal current flow with respect to the first and second nodes.

7. A device in accordance with claim 6, wherein the first and fourth probes are disposed on a first single probe body, but define separate electrical paths with separate electrical contact points;

and wherein the second and fifth probes are disposed on a second single probe body, but define separate electrical paths with separate electrical contact points; and

wherein the third and sixth probes are disposed on a third single probe body, but define separate electrical paths with separate electrical contact points.

8. A device in accordance with claim 1, wherein the first and second probes include a pair of arms pivotally coupled at one end.

9. A device in accordance with claim 1, further comprising:

a signal processor, connected to the at least one current source and the at least one voltage meter, configured to calculate the impedance of the component based on the known values of the current and measured values of the voltage.

10. A device in accordance with claim 1, wherein the at least one voltage meter includes:

a) analog-to-digital circuitry configured to convert voltages to digital values; and

b) wherein the processor includes a digital signal processor, connected to the analog-to-digital circuitry, configured to separate the voltage measurements.

11. A device in accordance with claim 1, further comprising:

a) an input device configured to receive input from a user to control the device;

b) a display configured to display information; and

c) a port configured to transfer data.

12. A device in accordance with claim 1, further comprising:

a) a reference resistor, selectively connected to the at least one current source and the at least one voltage meter, to calibrate the device; and

b) at least one switch, connected between the reference resistor and the at least one current source and the at least one voltage meter, to selectively connect the at least one current source and the at least one voltage meter to the reference resistor or probes.

13. A device in accordance with claim 1, wherein the at least one current source includes a plurality of unbalanced resistors to create an internal shunt.

14. A device in accordance with claim 1, further comprising:

a measurement device to determine current to verify proper contact.

15. An impedance measurement device, comprising:

a) a circuit having first and second nodes, and at least one parallel current path which experiences an equal current flow with respect to the first and second nodes;

b) first and second probes, contacting the respective first and second nodes;

c) a third common probe, contacting the circuit at a common node at a location that experiences equal current flow with respect to the first and second nodes;

d) at least one current source, connected to the at least first and second probes, configured to provide first and second currents of known values to be applied to the respective first and second nodes; and

e) at least one voltage meter, configured to be connected to the first and second nodes, to measure voltages corresponding to the first and second currents.

16. A device in accordance with claim 15, wherein the at least one current source is configured to provide different first and second current signals.

17. A device in accordance with claim 15, wherein the at least one current source is configured to provide different sinusoidal current signals.

18. A device in accordance with claim 15, further comprising:

a signal processor, coupled to the at least one voltage meter and configured to be connected to the first and second nodes, and configured to isolate the voltages measured by the at least one voltage meter from the first and second currents, and to calculate the impedance of the component based on the known values of the first and second currents and the measured voltages.

19. A device in accordance with claim 15, wherein the at least one voltage meter is connected to the respective first and second probes, and both are connected to the third probe.

20. A device in accordance with claim 15, further comprising:

a) a fourth probe, connected to the at least one voltage meter, and configured to contact the first node;

b) a fifth probe, connected to the at least one voltage meter, and configured to contact the second node; and

c) a sixth common probe, connected to the at least one voltage meters, and configured to contact the circuit at the common location.

21. A device in accordance with claim 20, wherein the first and fourth probes are disposed on a first single probe body, but define separate electrical paths with separate electrical contact points;

and wherein the second and fifth probes are disposed on a second single probe body, but define separate electrical paths with separate electrical contact points; and

wherein the third and sixth probes are disposed on a third single probe body, but define separate electrical paths with separate electrical contact points.

22. A device in accordance with claim 15, wherein the first and second probes include a pair of arms pivotally coupled at one end.

23. A device in accordance with claim 15, further comprising:

a signal processor, connected to the at least one current source and the at least one voltage meter, configured to calculate the impedance of the component based on the known values of the current and measured values of the voltage.

24. A device in accordance with claim 15, wherein the at least one voltage meter includes:

a) analog-to-digital circuitry configured to convert voltages to digital values; and

b) a digital signal processor, connected to the analog-to-digital circuitry, configured to separate the voltage measurements and calculate the impedance between the first and second nodes based on the known values of the current and measured values of the voltage.

25. A device in accordance with claim 15, further comprising:

a) an input device configured to receive input to control the device;

b) a display configured to display information; and

c) a port configured to transfer data.

26. A device in accordance with claim 15, further comprising:

a) a reference resistor, selectively connected to the at least one current source and the at least one voltage meter, to calibrate the device; and

b) at least one switch, connected between the reference resistor and that at least one current source and the at least one voltage, to selectively connect the at least one current source and the at least one voltage meter to the reference resistor or probes.

27. A device in accordance with claim 15, wherein the at least one current source includes a plurality of unbalance resistors to create an internal shunt.

28. A device in accordance with claim 15, further comprising:

a measurement device to determine current to verify proper contact.

29. A method for measuring an impedance between first and second nodes of an electrical circuit without removing components from the circuit, the method comprising the steps of:

a) selecting first and second nodes within the circuit;

b) selecting a common node at a location different from the first and second nodes and that has a concurrent current flow equal in value to current flow between the first and second nodes;

c) applying first and second currents of known values at the respective first and second nodes;

d) measuring at least four voltages, including;

i) a voltage between the first and common nodes measured at the first node caused by the first current;

ii) a voltage between the first and common nodes measured at the first node caused by the second current;

iii) a voltage between the second and common nodes measured at the second node caused by the first current; and

iv) a voltage between the second and common nodes measured at the second node caused by the second current; and

e) calculating the impedance based on known values of currents and measured values voltages.

30. A method in accordance with claim 29, wherein the step of calculating the impedance further includes:

a) treating the first and second nodes as a cross member of a pi network; and

b) treating remaining circuitry of both the electrical circuit and measurement device as side shunts of the pi network containing the parallel effects of all components in the electrical circuit and measurement device.

31. A method in accordance with claim 29, further comprising the step of using a trace or via as a shunt element to separate parallel components.

32. A method in accordance with claim 29, wherein the step of applying first and second currents includes:

contacting the first and second nodes with at least respective first and second probes; and

contacting the common node with at least a third common probe.

33. A method in accordance with claim 32, wherein the step of measuring the voltages includes:

contacting the first and second nodes with at least respective fourth and fifth probes; and

contacting the common node with at least a sixth common probe.

34. A method in accordance with claim 29, wherein the step of applying first and second currents further includes applying different first and second current signals.

35. A method in accordance with claim 29, wherein the step of applying first and second currents further includes applying different sinusoidal current signals.

36. A method in accordance with claim 29, further comprising the step of:

separating the voltages corresponding to the first and second currents at the first and second nodes.

37. A method in accordance with claim 29, further comprising the steps of:

a) activating the circuit and analyzing system signals present in the circuit prior to applying the currents;

b) selecting frequencies for the currents which will not conflict with the system signals or which will have predictable conflicts with the system signals prior to applying the currents; and

c) separating the voltages caused by the currents.

38. A method in accordance with claim 29, further comprising the step of:

calibrating by switching the current sources and voltage meters to a reference resistor.

39. A method in accordance with claim 29, further comprising the step of:

verifying proper contact by determining the current.

40. A method in accordance with claim 29, further comprising the step of:

providing an internal shunt by unbalancing a plurality of resistors forming the current sources.

41. A method in accordance with claim 29, wherein the step of calculating the impedance further includes:

calculating the impedance utilizing the formula

42. A method in accordance with claim 29, wherein the step of calculating the impedance further includes:

calculating the impedance utilizing the formula

43. A method for measuring an impedance between first and second nodes in an electrical circuit, the method comprising the steps of:

a) contacting the first and second nodes with first and second probes;

b) selecting a common node at a location which experiences an equal current flow with respect to the first and second nodes;

c) contacting the common node with a third probe;

d) applying a first current of known value at the first node;

e) applying a second current of known value at the second node;

f) measuring a first voltage at the first node due to the first current;

g) measuring a second voltage at the first node due to the second current source;

h) measuring a third voltage at the second node due to the second current source;

i) measuring a fourth voltage at the second node due to the first current source; and

j) calculating the impedance of the component based on the known values of the first and second currents and the measured values of the first, second, third and fourth voltages.

44. A method in accordance with claim 43, wherein the step of calculating the impedance further includes:

a) treating the first and second nodes as a cross member of a pi network; and

b) treating remaining circuitry of both the electrical circuit and measurement device as side shunts of the pi network containing the parallel effects of all components in the circuit and the loading of the measurement device.

45. A method in accordance with claim 43, further comprising the step of using a trace or via as a shunt element to separate parallel components.

46. A method in accordance with claim 43, wherein the step of measuring the voltages includes:

contacting the first and second nodes with at least respective fourth and fifth probes; and

contacting the common node with at least a sixth common probe.

47. A method in accordance with claim 43, wherein the step of calculating the impedance further includes:

calculating the impedance utilizing the formula

48. A method in accordance with claim 43, wherein the step of calculating the impedance further includes:

calculating the impedance utilizing the formula

 

Z₂=((V₁₁*V₀₀/V₁₀)−

V₀₁)/I₁

 

where

Z₂ is the impedance of the component;

V₀₀ is the voltage measured at the first node caused by the first current;

V₀₁ is the voltage measured at the first node caused by the second current;

V₁₀ is the voltage measured at the second node caused by the first current;

V₁₁ is the voltage measured at the second node caused by the second current; and

I₁ is the second current.

49. A method in accordance with claim 43, wherein the steps of applying first and second currents further includes applying different first and second current signals.

50. A method in accordance with claim 43, wherein the steps of applying first and second currents further includes applying different sinusoidal current signals.

51. A method in accordance with claim 43, further comprising the step of:

separating the voltages corresponding to the first and second currents at the first and second nodes.

52. A method in accordance with claim 43, further comprising the steps of:

a) activating the circuit and analyzing system signals present in the circuit prior to applying the currents;

b) selecting frequencies for the currents which will not conflict with the system signals or which will have predictable conflicts with the system signals prior to applying the currents; and

c) separating the voltages caused by the currents.

53. A method in accordance with claim 43, further comprising the step of:

calibrating by switching the current sources and voltage meters to a reference resistor.

54. A method in accordance with claim 43, further comprising the step of:

verifying proper contact by determining the current.

55. A method in accordance with claim 43, further comprising the step of:

providing an internal shunt by unbalancing a plurality of resistors forming the current sources.

56. A device configured to measure an impedance between first and second nodes in an electrical circuit, the device comprising:

a) a voltage source configured to provide a voltage of known value;

b) a current source configured to provide a current of known value;

c) first and second probes, each connected to one of the voltage and current sources, and configured to contact the respective first and second nodes to apply the voltage and current to the first and second nodes;

d) a third common probe, connected to the voltage and current sources, configured to contact the circuit at a common node at a location that has an equal current flow with respect to the first and second nodes;

e) at least one voltage meter, configured to be connected to the first and second nodes, to measure voltages corresponding to the known voltage and current; and

f) a processor, operatively coupled to the voltage and current sources and the at least one voltage meter, capable of calculating the impedance based on the known values of the voltage and current and the measured values of the voltages.

57. A method for measuring an impedance between first and second nodes in an electrical circuit, the method comprising the steps of:

a) contacting the first and second nodes with first and second probes;

b) selecting a common node at a location which experiences an equal current flow with respect to the first and second nodes;

c) contacting the common node with a third probe;

d) applying a known current at the first node;

e) applying a known voltage at the second node;

f) measuring at least three voltages, including;

i) a voltage between the first and common nodes measured at the first node caused by the known current;

ii) a voltage between the first and common nodes measured at the first node caused by the known voltage; and

iii) a voltage between the second and common nodes measured at the second node caused by the known current; and

g) calculating the impedance based on the known current and voltage and the measured values of the at least three voltages.