Current measurement techniques to compensate for shunt drift

• US 10,359,449 B2
• Filed: 03/29/2017
• Issued: 07/23/2019
• Est. Priority Date: 03/29/2017
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices, Inc.
• Inventors: Callanan, Andreas
• Primary Examiner(s): Nguyen, Tung X
• Application Number:
  US15/472,706
• Publication Number:
  US 20180284159A1
• Time in Patent Office: 846 Days
• CPC Class Codes: G01R 15/146 Measuring arrangements for current not covered by other subgroups of G01R15/14, e.g. using current dividers, shunts, or measuring a voltage drop if no voltage isolation is involved G01R1/203 or G01R19/0092
• CPC Class Codes: G01R 19/2506 Arrangements for conditioning or analysing measured signals, e.g. for indicating peak values G01R19/003 takes precedence; Details concerning sampling, digitizing or waveform capturing displaying waveforms G01R13/00; analog sampling G01R19/0053
• CPC Class Codes: G01R 27/00 Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
• CPC Class Codes: G01R 31/364 Battery terminal connectors with integrated measuring arrangements
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

Described are various current measurement techniques that can compensate for drift in shunt resistance. Determining a resistance of a shunt resistor, e.g., coupled to a battery terminal, can include introducing a known signal in sync with the chop phases of a dual system chop scheme, chopping the known signal out in the main signal path, and explicitly extracting the known signal in a parallel, additional signal deprocessing path.

Claims

1. A method of determining a resistance of a shunt resistor coupled to a battery terminal, the method comprising:

receiving an input signal corresponding to a voltage across the shunt resistor;

during a first conversion cycle in the absence of a stimulus applied to the shunt resistor and during a second conversion cycle in the presence of the stimulus applied to the shunt resistor;

generating a first digital signal using a combination of a chopped input signal and an offset error;

determining a first output signal using a de-chopped first digital signal; and

determining a second output signal using the first digital signal; and

determining the resistance of the shunt resistor using the first and second output signals from the first and second conversion cycles.

2. The method of claim 1, comprising:

determining a battery current using the first and second output signals.

3. The method of claim 1, wherein determining a first output signal using a de-chopped first digital signal includes:

filtering, using a first channel, the de-chopped first digital signal to determine the first output signal, and

wherein determining a second output signal using the first digital signal includes;

filtering, using a second channel, the first digital signal to determine the second output signal.

4. The method of claim 1, comprising:

applying a current having a specified value from a current source through the shunt resistor.

5. The method of claim 1, comprising:

applying a current through the shunt resistor using first and second wires of a 4-wire measurement system.

6. The method of claim 5, wherein applying a current through the shunt resistor using first and second wires of a 4-wire measurement system includes:

during alternating chop phases of the second conversion cycle, de-chopping the current.

7. The method of claim 1, comprising:

applying a current through the shunt resistor using a first wire of a 3-wire measurement system.

8. The method of claim 1, wherein the applied stimulus through the shunt resistor is a first current, the method further comprising:

before the first conversion cycle, applying a second current through the shunt resistor, wherein the first current is different from the second current.

9. The method of claim 1, comprising:

applying a current through the shunt resistor including;

during a first chop phase of the second conversion cycle, applying the current having a first polarity; and

during a second chop phase of the second conversion cycle, applying the current having a polarity opposite the first polarity.

10. An apparatus for determining a resistance of a shunt resistor coupled to a battery terminal, the apparatus comprising:

a measurement channel circuit configured to receive a chopped input signal corresponding to a voltage across the shunt resistor and to generate a first digital signal using a combination of the chopped input signal and an offset error during a first conversion cycle in the absence of a stimulus applied to the shunt resistor and during a second conversion cycle in the presence of the stimulus applied to the shunt resistor;

a first output channel circuit coupled to the output of the measurement channel circuit and configured to determine a first output signal using a de-chopped first digital signal for the first and second conversion cycles;

a second output channel circuit coupled to the output of the measurement channel circuit and configured to determine a second output signal using the first digital signal for the first and second conversion cycles; and

a processor configured to determine the resistance of the shunt resistor using the first and second output signals from the first and second conversion cycles.

11. The apparatus of claim 10, wherein the stimulus applied is a current.

12. The apparatus of claim 10, wherein the processor is configured to determine a battery current using the first and second output signals.

13. The apparatus of claim 10, further comprising:

an input chopping switch network configured to receive and chop the input signal,

wherein the first output channel circuit includes an output chopping switch network coupled to an output of the measurement channel circuit and configured to de-chop the first digital signal.

14. The apparatus of claim 10, comprising:

a 4-wire measurement system coupled to first and second terminals of the shunt resistor.

15. The apparatus of claim 14, further comprising:

a stimulus source to supply the applied stimulus, wherein the stimulus source is configured to invert the stimulus during alternating chop phases of the second conversion cycle.

16. The apparatus of claim 10, comprising:

a 3-wire measurement system coupled to first and second terminals of the shunt resistor.

17. The apparatus of claim 10, wherein the first output channel circuit includes a first digital filter, wherein the second output channel circuit includes a second digital filter, and wherein at least one of the first digital filter and the second digital filter includes a sinc filter.

18. An apparatus for determining a resistance of a shunt resistor coupled to a battery terminal, the apparatus comprising:

means for receiving an input signal corresponding to a voltage across the shunt resistor;

means for generating a first digital signal using a combination of a chopped input signal and an offset error during a first conversion cycle in the absence of a stimulus applied to the shunt resistor and during a second conversion cycle in the presence of the stimulus applied to the shunt resistor;

means for determining a first output signal using a de-chopped first digital signal for the first and second conversion cycles; and

means for determining a second output signal using the first digital signal for the first and second conversion cycles; and

means for determining the resistance of the shunt resistor using the first and second output signals.

19. The apparatus of claim 18, comprising:

means for determining a battery current using the first and second output signals.

20. The apparatus of claim 18, comprising:

means for applying a current having a known value from a current source through the shunt resistor.