Systems and methods for utilizing intrinsic current noise to measure interface impedances
The disclosed computer-implemented method may include (1) sampling an output signal of an amplifier that amplifies a voltage difference between two electrodes, (2) calculating, based on a power spectral density of the output signal, a noise power of the output signal over a predetermined frequency band, (3) estimating an interface impedance of at least one of the two electrodes based on the noise power and a predetermined intrinsic current noise of the amplifier, and (4) performing an operation based at least in part on the estimated interface impedance. Various other methods, systems, and devices are also disclosed.
1. A wearable device for detecting neuromuscular activity, comprising:
at least two dry electrodes configured to electrically couple to an external body surface of a wearer of the wearable device;
signal-amplifying circuitry configured to amplify electrical signals from the at least two dry electrodes; and
impedance-measuring circuitry that:
estimates an interface impedance of at least one of the two dry electrodes based on a spectral density of an output signal of the signal-amplifying circuitry and a predetermined intrinsic current noise of the signal-amplifying circuitry; and
performing an operation based at least in part on the estimated interface impedance.
2. The wearable device of claim 1 , wherein the electrically coupling includes physical contact between the at least two dry electrodes and the external body surface of the wearer.
3. The wearable device of claim 1 , wherein the electrically coupling includes capacitive coupling between the at least two dry electrodes and the external body surface of the wearer.
4. The wearable device of claim 1 , wherein the impedance-measuring circuitry estimates the interface impedance by:
calculating a power spectral density of the output signal;
calculating, using the power spectral density, a noise power of the output signal over a predetermined frequency band; and
estimating the interface impedance based on the noise power.
5. The wearable device of claim 1 , wherein the signal-amplifying circuitry comprises a differential amplifier.
6. The wearable device of claim 1 wherein:
the at least two dry electrodes comprise a pair of dry electrodes; and
the electrical signals comprise differential signals received by the pair of dry electrodes.
7. The wearable device of claim 6 , wherein the at least two dry electrodes further comprise a dry ground electrode configured to receive ground signals from which the differential signals are referenced.
8. A non-transitory computer-readable storage medium, comprising instructions that, when executed by a wearable device that includes (i) at least two dry electrodes that are electrically coupled to an external body surface of a wearer of the wearable device, (ii) signal-amplifying circuitry, and (iii) impedance-measuring circuitry, cause operations for:
amplifying, using the signal-amplifying circuitry, electrical signals from the at least two dry electrodes; and
using the impedance-measuring circuitry:
estimating an interface impedance of at least one of the two dry electrodes based on a spectral density of an output signal of the signal-amplifying circuitry and a predetermined intrinsic current noise of the signal-amplifying circuitry; and
performing an operation based at least in part on the estimated interface impedance.
9. The non-transitory computer-readable storage medium of claim 8 , wherein the electrically coupling includes physical contact between the at least two dry electrodes and the external body surface of the wearer.
10. The non-transitory computer-readable storage medium of claim 8 , wherein the electrically coupling includes capacitive coupling between the at least two dry electrodes and the external body surface of the wearer.
11. The non-transitory computer-readable storage medium of claim 8 , further comprising instructions for:
using the impedance-measuring circuitry:
calculating a power spectral density of the output signal;
calculating, using the power spectral density, a noise power of the output signal over a predetermined frequency band; and
estimating the interface impedance based on the noise power.
12. The non-transitory computer-readable storage medium of claim 8 , wherein the signal-amplifying circuitry comprises a differential amplifier.
13. The non-transitory computer-readable storage medium of claim 8 , wherein:
the at least two dry electrodes comprise a pair of dry electrodes; and
the electrical signals comprise differential signals received by the pair of dry electrodes.
14. The non-transitory computer-readable storage medium of claim 13 , wherein the at least two dry electrodes further comprise a dry ground electrode configured to receive ground signals from which the differential signals are referenced.
15. A method, comprising:
at a wearable device comprising (i) at least two dry electrodes that are electrically coupled to an external body surface of a wearer of the wearable device, (ii) signal-amplifying circuitry, and (iii) impedance-measuring circuitry, (iv) one or more processors, and (v) memory, comprising instructions which, when executed by the one or more processors, cause operations comprising:
amplifying, using the signal-amplifying circuitry, electrical signals from the at least two dry electrodes; and
using the impedance-measuring circuitry:
estimating an interface impedance of at least one of the two dry electrodes based on a spectral density of an output signal of the signal-amplifying circuitry and a predetermined intrinsic current noise of the signal-amplifying circuitry; and
performing an operation based at least in part on the estimated interface impedance.
16. The method of claim 15 , wherein the electrically coupling includes physical contact between the at least two dry electrodes and the external body surface of the wearer.
17. The method of claim 15 , wherein the memory further comprises instructions for:
using the impedance-measuring circuitry:
calculating a power spectral density of the output signal;
calculating, using the power spectral density, a noise power of the output signal over a predetermined frequency band; and
estimating the interface impedance based on the noise power.
18. The method of claim 15 , wherein the signal-amplifying circuitry comprises a differential amplifier.
19. The method of claim 15 , wherein:
the at least two dry electrodes comprise a pair of dry electrodes; and
the electrical signals comprise differential signals received by the pair of dry electrodes.
20. The method of claim 19 , wherein the at least two dry electrodes further comprise a dry ground electrode configured to receive ground signals from which the differential signals are referenced.