Selctable notch filter circuits

• US 20040199082A1
• Filed: 04/03/2003
• Published: 10/07/2004
• Est. Priority Date: 04/03/2003
• Status: Abandoned Application

• Current Assignee: Cameron Incorporated (Schlumberger NV)
• Original Assignee: Cameron Incorporated (Schlumberger NV)
• Inventors: Ostroff, Alan H., Phillips, James William
• Application Number:
  US10/406,454
• Publication Number:
  US 20040199082A1
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: H03H 17/0294 Variable filters; Programmable filters

Abstract

Described are selectable notch filter circuits comprising at least two different notch filter capabilities, each of which is capable of filtering interference of a designated fundamental frequency and a second harmonic of the designated fundamental frequency from an electrical signal. Each of the notch filters of the circuit is specific for real time filtering of a different designated fundamental frequency and a second harmonic thereof from digitized signal data input into the circuit. The filtering capability of each filter is dictated by control logic, which uses a coefficient set specific for the designated fundamental frequency and harmonics thereof. By using different coefficient sets, different designated fundamental frequencies and at least their second harmonic frequencies can be filtered from digitized signal data input into the circuit. Because the control logic can utilize at a given time any one (or, if desired, none) of the coefficient sets available to it, different interfering fundamental frequencies can be filtered, if and as necessary, from digitized input signal data collected over time at a substantially equivalent sampling rate. Also described are devices including one or more such selectable notch filter circuits, including implantable medical devices such as implantable cardioverter/defibrillators, as well as methods of using such devices.

Claims

1. A circuit comprising hardware configured to serve at a given time as a selected one of a plurality of notch filters each of which is specific for filtering in real time from digitized input signal data input into the circuit a different designated fundamental frequency and a second harmonic thereof, wherein embedded in the hardware is control logic that controls filtering of a sampled designated fundamental frequency by using a coefficient set specific for the sampled designated fundamental frequency selected from among a plurality of coefficient sets each specific for a different designated fundamental frequency, and wherein each of the notch filters operates on digitized input signal data sampled at a substantially equivalent sampling rate.

2. A circuit according to claim 1 wherein the designated fundamental frequency is about 60 Hz.

3. A circuit according to claim 1 wherein the designated fundamental frequency is about 50 Hz.

4. A circuit according to claim 1 wherein one of the notch filters is specific for filtering a designated fundamental frequency of about 60 Hz and another of the notch filters is specific for filtering a designated fundamental frequency of about 50 Hz.

5. A circuit according to claim 1 wherein the sampling rate is greater than about 240 Hz.

6. A circuit according to claim 1 wherein the sampling rate is between about 240 Hz and about 2,400 Hz.

7. A circuit according to claim 1 wherein the sampling rate is greater than about 240 Hz and less than about 600 Hz.

8. A circuit according to claim 7 wherein the sampling rate is about 256 Hz.

9. A circuit according to claim 2 wherein the coefficient set comprises coefficients A, B, C, D, E, and F for solving a transfer function defined by Eq. (1), as follows:

10. A circuit according to claim 9 wherein coefficient A is about ⅞

or a decimal representation thereof, coefficient B is about {fraction (21/128)} or a decimal representation thereof, coefficient C is about ¼

or a decimal representation thereof, coefficient D is about {fraction (31/64)} or a decimal representation thereof, coefficient E is about {fraction (3/16)} or a decimal representation thereof, and coefficient F is about ¾

or a decimal representation thereof.

11. A circuit according to claim 3 wherein the coefficient set comprises coefficients A, B, C, D, E, and F for solving a transfer function defined by Eq. (1), as follows:

12. A circuit according to claim 11 wherein coefficient A is about {fraction (115/128)} or a decimal representation thereof, coefficient B is about {fraction (79/128)} or a decimal representation thereof, coefficient C is about {fraction (9/32)} or a decimal representation thereof, coefficient D is about {fraction (7/16)} or a decimal representation thereof, coefficient E is about {fraction (9/16)} or a decimal representation thereof, and coefficient F is about ¾

or a decimal representation thereof.

13. A circuit according to claim 1 wherein the control logic implements a transfer function that utilizes a floating point calculation.

14. A circuit according to claim 1 wherein the hardware further comprises the coefficient set specific for the sampled designated fundamental frequency embedded therein.

15. A circuit according to claim 1 wherein the control logic is capable of accessing at least one of the coefficient sets from a memory operably associated with but separate from the circuit.

16. A selectable notch filter circuit for an implantable medical device, comprising:

a. an input for a digitized electrical signal and an output for the digitized electrical signal;

b. disposed between the input and output, hardware configured to serve at a given time as a selected one of a plurality of notch filters each of which is specific for filtering in real time from the digitized electrical signal input into the circuit a different designated noise fundamental frequency and a second harmonic thereof, wherein embedded in the hardware is control logic that controls filtering of a sampled designated noise fundamental frequency by using a coefficient set specific for the sampled designated noise fundamental frequency selected from among a plurality of coefficient sets each specific for a different designated noise fundamental frequency, and wherein each of the notch filters operates on digitized input signal data sampled at a substantially equivalent sampling rate; and

c. a selector that selects which of the plurality of coefficient sets to be utilized at a given time by the control logic.

17. A selectable notch filter circuit according to claim 16 further comprising a filter bypass for the digitized electrical signal input into the circuit.

18. A selectable notch filter circuit according to claim 17 wherein the selector is capable of selecting the filter bypass.

19. A selectable notch filter circuit according to claim 16 that is operatively connected with circuitry for sensing a physiological parameter of a patient by analysis of the digitized electrical signal.

20. A selectable notch filter circuit according to claim 19 that is operatively associated with circuitry for administering a therapy to the patient if the analysis of the digitized electrical signal is indicative of an abnormal condition.

21. An implantable medical device the circuitry of which contains a selectable notch filter circuit according to claim 16.

22. An implantable medical device the circuitry of which contains a plurality of selectable notch filter circuits each of which is a selectable notch filter circuit according to claim 16.

23. An implantable medical device according to claim 21 for sensing a physiological parameter of a patient.

24. An implantable medical device according to claim 23 that further is capable of administering a therapy to the patient if an analysis of the sensed physiological parameter is indicative of an abnormal condition for sensing a physiological parameter of a patient.

25. An implantable medical device according to claim 23 wherein the physiological parameter is a heart beat.

26. An implantable medical device according to claim 24 wherein the abnormal condition is an arrhythmia.

27. An implantable medical device according to claim 26 wherein the arrhythmia is selected from the group consisting of bradycardia and tachyarrhythmia.

28. An implantable medical device according to claim 27 that is an implantable cardioverter-defibrillator.

29. An implantable cardioverter-defibrillator according to claim 27 that is implanted subcutaneously in a patient.

30. An implantable cardioverter-defibrillator according to claim 29 that does not make physical contact with heart tissue after implantation in the patient.

31. A heart-specific sensing system for an implantable medical device, comprising:

a. an electrode for sensing electrical signals within a patient'"'"'s body;

b. an analog-to-digital converter for converting a sensed electrical signal to a digitized electrical signal;

c. a selectable notch filter circuit according to claim 16;

and

d. a detector to detect whether the digitized electrical signal contains a heart-specific component.

32. A heart-specific sensing system according to claim 31 wherein the detector is an R-wave detector.

33. An implantable cardioverter-defibrillator, comprising:

a. a sense electrode for sensing electrical signals within a patient'"'"'s body;

b. an analog-to-digital converter for converting a sensed electrical signal to a digitized electrical signal;

c. a selectable notch filter circuit according to claim 16;

d. a detector to detect whether the digitized electrical signal contains a heart-specific component;

e. a therapy electrode for delivering a therapeutic electrical stimulus to the patient'"'"'s heart when the detector detects in the digitized electrical signal a heart-specific component that is indicative of an abnormal heart rhythm;

f. a power supply; and

g. a housing that houses at least foregoing parts (c), (d), and (f).

34. An implantable cardioverter-defibrillator according to claim 33 that is a subcutaneous unitary cardioverter-defibrillator.

35. A method for filtering an external noise component from a digitized electrical signal in an implantable medical device, comprising:

a. obtaining a digitized electrical signal; and

b. passing the digitized electrical signal through a selectable notch filter circuit according to claim 16.

36. A method according to claim 35 wherein the notch filter initially selected is a default setting.

37. A method according to claim 36 wherein the default setting corresponds to a fundamental frequency of a local AC power supply or a no-filtering function.

38. A method according to claim 37 wherein the fundamental frequency of the local AC power supply is 60 Hz.

39. A method according to claim 37 wherein the fundamental frequency of the local AC power supply is 50 Hz.

40. A method according to claim 35 that is performed intermittently.

41. A method for sensing a physiological parameter of a patient, comprising using an implantable medical device according to claim 23 for sensing the physiological parameter.

42. A method for delivering a therapy to a patient, comprising using an implantable medical device according to claim 24 to deliver the therapy when the sensed physiological parameter indicates that an abnormal condition exists.