System and method for detecting defects within an electrical circuit by analyzing quiescent current

• US 6,366,108 B2
• Filed: 12/01/1998
• Issued: 04/02/2002
• Est. Priority Date: 12/01/1998
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Maxwell, Peter, Johansen, Victor, OʼNeill, Peter M.
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): KERVEROS, DEMETRIOS C
• Application Number:
  US09/203,295
• Publication Number:
  US 20010011903A1
• Time in Patent Office: 1,218 Days
• Field of Search: 324/763, 324/765, 324/768, 324/769, 324/771
• US Class Current: 324/762.02
• CPC Class Codes: G01R 31/3004 Current or voltage test
• CPC Class Codes: G01R 31/3008 Quiescent current [IDDQ] test or leakage current test
• CPC Class Codes: G06F 2201/81 Threshold

Abstract

The present invention, in general, provides for a testing system and method for detecting defects within a circuit. A current signature of the quiescent current of the circuit is determined, and certain constant values are calculated based on the current signature using a linear iterative regression. A defect free state for the circuit associated with a minimum quiescent current (I_DDQ) is then determined. The I_DDQ of the circuit for this state is measured, and a signal indicating the I_DDQ at this state is used along with the aforementioned constant values to create upper and lower threshold values. Thereafter, signals indicating the value of I_DDQ for a plurality of other states are compared to the upper and lower threshold values. The circuit is determined to be defective if the values of any of the signals is greater than the upper threshold value or is less than the lower threshold value.

Claims

1. A system for detecting defects within circuits, the system comprising:

a power supply unit, said power supply unit configured to transmit supply current to a circuit coupled to said power supply unit;

a current meter configured to receive and measure said supply current, said current meter further configured to transmit signals indicative of values measured from said supply current; and

an analyzer interfaced with said current meter and configured to test a plurality of circuits, said analyzer storing a test value that is based on measured supply currents transmitted to another plurality of circuits, said analyzer further configured to automatically calculate a different threshold value for each of said circuits tested by said analyzer, said analyzer configured to calculate said different threshold value for said each respective circuit utilizing said test value and a value measured by said current meter as said power supply unit is transmitting supply current to said each respective circuit, said analyzer further configured to perform a comparison of said threshold value determined for said each respective circuit to one of said signals transmitted by said current meter, said one signal indicative of a value measured by said current meter as said power supply unit is transmitting supply current to said each respective circuit, said analyzer further configured to determine whether said each respective circuit is defective based on said comparison performed for said each respective circuit.

2. A method for detecting defects within circuits, the method comprising the steps of:

providing a plurality of circuits;

modeling current signatures for said plurality of circuits;

analyzing said current signatures;

determining a test value based on said analyzing step;

measuring a value of a supply current transmitted to a circuit under test when said circuit under test is in a first quiescent state;

determining a threshold value based on said test value and said value of said supply current measured in said measuring step;

receiving a signal indicating another value of said supply current when said circuit under test is in a second quiescent state;

comparing said signal to said threshold value; and

detecting a defect in said circuit under test based on said comparing step.

3. The method of claim 2, further comprising the steps of:

determining a second threshold value based on said value of said supply current measured in said measuring step; and

comparing said signal to said second threshold value.

4. The method of claim 2, further comprising the step of refraining from determining a value of said signal.

5. The method of claim 2, further comprising the step of:

selecting said first quiescent state based on said current signatures, wherein

said measuring step is based on said selecting step.

6. The method of claim 2, further comprising the steps of:

providing a second circuit;

measuring a value of a supply current transmitted to said second circuit when said second circuit is in said first quiescent state;

determining a new threshold value based on said test value and said value of said supply current transmitted to said second circuit;

receiving a signal indicating another value of said supply current transmitted to said second circuit when said second circuit is in another quiescent state;

comparing said new threshold value to said signal that is indicating said other value of said supply current transmitted to said second circuit; and

detecting whether a defect exists in said second circuit based on said comparing said new threshold value step.

7. The method of claim 2, wherein said analyzing step includes the steps of:

selecting a first value and a second value from each of said current signatures;

plotting, for each of said current signatures, said first value versus said second value to define a graph; and

performing a regression of said graph,

wherein said determining a test value step is based on said regression.

8. The method of claim 7, wherein said first value is a maximum value of said each current signature, and wherein said second value is a minimum value of said each current signature.

9. The method of claim 7, further comprising the steps of:

selecting said first quiescent state based on said current signatures; and

placing said circuit in said first quiescent state based on said selecting step,

wherein said measuring step is performed in response to said placing step.

10. The method of claim 7, further comprising the step of:

removing outliers from said graph.

11. The method of claim 2, wherein said determining a threshold value step is based on the following equation:

12. The system of claim 11 wherein m represents the slope of a line fitted to said current signatures.

13. A method for detecting defects within circuits, the method comprising the steps of:

providing a plurality of circuits;

producing signals indicating values of supply currents transmitted to different ones of said circuits when said different ones of said circuits are in quiescent states;

analyzing values of said signals;

determining a constant value based on said analyzing step;

selecting a circuit;

placing said circuit into a first state;

producing a first signal indicating a first value of a supply current of said circuit when said circuit is in said first state;

determining a threshold value based on said constant value and said first signal;

placing said first circuit into another state;

producing a second signal indicating a second value of said supply current when said circuit is in said other state; and

determining whether a value of said second signal exceeds said first threshold value.

14. The method of claim 13, further comprising the steps of:

determining a second threshold value for said circuit based on said first signal; and

determining whether said value of said second signal exceeds said second threshold value.

15. The method of claim 13, further comprising the steps of:

selecting a first respective value and a second respective value of said values analyzed in said analyzing step for each of said plurality of circuits;

plotting, for each of said circuits, said first respective value versus said second respective value; and

performing a regression of said values plotted in said plotting step,

wherein said determining a constant value step is based on said plotting step and said performing a regression step.

16. The method of claim 13, wherein said placing said circuit into a first state step is performed subsequent to said determining a constant value step.

17. A method for detecting defects within circuits, the method comprising the steps of:

providing a plurality of circuits;

modeling a current signature for each of said plurality of circuits;

analyzing each current signature modeled in said modeling step;

determining a plurality of values based on said analyzing step;

selecting a state based on current signatures modeled in said modeling step;

a value of a supply current transmitted to a circuit under test when said circuit under test is in said selected state;

determining a threshold value based on said plurality of values and said value of said supply current measured in said measuring a value of a supply current step;

measuring another value of said supply current when said circuit under test is in another state;

comparing said other value to said threshold value; and

detecting whether said circuit under test is defective based on said comparing step.

18. The method of claim 17, further comprising the steps of:

selecting a first value and a second value from each current signature modeled in said modeling step; and

plotting, for each current signature modeled in said modeling step, said first value and said second value to define a graph.

wherein said plurality of values determined based on said analyzing step includes a slope of said graph and an outlier margin value associated with said graph.

19. A system for detecting defects within circuits, comprising:

a power supply unit configured to transmit supply current to a circuit coupled to said power supply unit;

a current meter configured to receive and measure said supply current, said current meter further configured to transmit signals indicative of values measured from said supply current; and

an analyzer interfaced with said current meter and configured to test said circuit, said analyzer storing a test value that is based on measured supply currents transmitted to a plurality of circuits, said analyzer configured to calculate automatically a threshold value for said circuit based on said stored test value and one of said signals, said one signal indicative of said supply current while said circuit is in a first quiescent state, said analyzer further configured to perform a comparison between said threshold value and a value of another of said signals, said other signal indicative of said supply current while said circuit is a second quiescent state, said analyzer further configured to indicate whether said circuit is defective based on said comparison.

20. The system of claim 19, wherein said analyzer is configured to calculate said threshold value based on the following equation:

21. The system of claim 19 wherein m represents the slope of a line fitted to current signatures of said plurality of circuits.