Chopper-stabilized instrumentation amplifier for impedance measurement

• US 9,615,744 B2
• Filed: 08/31/2010
• Issued: 04/11/2017
• Est. Priority Date: 01/31/2007
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Denison, Timothy J., Santa, Wesley A.
• Primary Examiner(s): Choe, Henry
• Application Number:
  US12/872,552
• Publication Number:
  US 20100327887A1
• Time in Patent Office: 2,415 Days
• Field of Search: 330 9, 330 10, 330 69
• CPC Class Codes: A61B 2560/0209 adapted for power saving
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/103 Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes A61B5/08 takes precedence; measuring aids for tailors A41H1/00; measuring instruments specially adapted for dentistry A61C19/04
• CPC Class Codes: A61B 5/30 Input circuits therefor
• CPC Class Codes: A61B 5/305 Common mode rejection
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7228 Signal modulation applied to the input signal sent to patient or subject; demodulation to recover the physiological signal modulation H03C
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control
• CPC Class Codes: A61N 2001/083 Monitoring integrity of contacts, e.g. by impedance measurement
• CPC Class Codes: G01R 27/04 in circuits having distributed constants , e.g. having very long conductors or involving high frequencies
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 2200/153 Feedback used to stabilise the amplifier
• CPC Class Codes: H03F 2200/252 Multiple switches coupled in the input circuit of an amplifier are controlled by a circuit, e.g. feedback circuitry being controlling the switch
• CPC Class Codes: H03F 2200/261 Amplifier which being suitable for instrumentation applications
• CPC Class Codes: H03F 2200/271 the DC-isolation amplifier, e.g. chopper amplifier, modulation/demodulation amplifier, uses capacitive isolation means, e.g. capacitors
• CPC Class Codes: H03F 2200/372 Noise reduction and elimination in amplifier
• CPC Class Codes: H03F 2200/375 Circuitry to compensate the offset being present in an amplifier
• CPC Class Codes: H03F 2203/45028 : the differential amplifier amplifying transistors are folded cascode coupled transistors
• CPC Class Codes: H03F 2203/45138 : Two or more differential amplifiers in IC-block form are combined, e.g. measuring amplifiers
• CPC Class Codes: H03F 2203/45212 : the differential amplifier being designed to have a reduced offset
• CPC Class Codes: H03F 2203/45264 : the dif amp comprising frequency or phase stabilisation means
• CPC Class Codes: H03F 2203/45396 : the AAC comprising one or more switches
• CPC Class Codes: H03F 2203/45512 : the FBC comprising one or more capacitors, not being switched capacitors, and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45534 : the FBC comprising multiple switches and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45551 : the IC comprising one or more switched capacitors
• CPC Class Codes: H03F 3/387 : with semiconductor devices only
• CPC Class Codes: H03F 3/45183 : Long tailed pairs H03F3/4521, H03F3/45237 take precedence
• CPC Class Codes: H03F 3/45192 : Folded cascode stages
• CPC Class Codes: H03F 3/45475 : using IC blocks as the active amplifying circuit
• CPC Class Codes: H03F 3/45744 : by offset reduction
• CPC Class Codes: H03F 3/45968 : by offset reduction

Abstract

In general, this disclosure is directed to a mixer amplifier that can be utilized within a chopper stabilized instrumentation amplifier. The chopper stabilized instrumentation amplifier may be used for physiological signal sensing, impedance sensing, telemetry or other test and measurement applications. In some examples, the mixer amplifier may include a current source configured to generate a modulated current at a modulation frequency for application to a load to produce an input signal, an amplifier configured to amplify the input signal to produce an amplified signal, and a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load.

Claims

1. An electrical impedance sensing device comprising:

a current source configured to generate a modulated current at a modulation frequency for application to a biological load to produce an input signal;

an amplifier configured to amplify the input signal to produce an amplified signal;

a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load;

first implantable electrodes coupled to apply the modulated current across the biological load; and

second implantable electrodes coupled to sense the input signal produced across the biological load.

2. The sensing device of claim 1, further comprising:

a modulator configured to modulate the output signal at the modulation frequency to produce a feedback signal; and

a feedback path that applies the feedback signal to the input signal.

3. The sensing device of claim 1, wherein the current source comprises a voltage source and a switch that modulates a current produced by the voltage source to produce the modulated current.

4. The sensing device of claim 1,

wherein the amplified signal is a current-mode signal,

wherein the demodulator is further configured to demodulate an amplitude of the amplified signal at the modulation frequency to produce a current-mode demodulated signal, and

wherein the sensing device further comprises a current-to-voltage converter configured to perform a current-to-voltage conversion operation on the demodulated signal to produce a voltage-mode output signal indicating the impedance of the biological load.

5. The sensing device of claim 4,

wherein the current-to-voltage converter comprises a resistance configured to perform the current-to-voltage conversion operation on the current-mode demodulated signal to produce the voltage-mode output signal, and

wherein the amplifier is further configured to amplify the input signal at a level of gain that is determined at least in part by a resistance value of the resistance.

6. The sensing device of claim 1,

wherein the sensing device further comprises a resistance coupled between a node carrying the output signal and a node regulated at a common voltage, and

wherein the amplifier is further configured to amplify the input signal at a level of gain that is determined at least in part by a resistance value of the resistance.

7. The sensing device of claim 6,

wherein the amplifier comprises a transconductor, and

wherein the level of gain is determined at least in part by the resistance value of the resistance and a transconductance of the transconductor.

8. The sensing device of claim 1,

wherein the demodulator is further configured to demodulate an amplitude of the amplified signal at the modulation frequency to produce a demodulated signal, and

wherein the sensing device further comprises a low-pass filter configured to perform a low-pass filtering operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

9. The sensing device of claim 8,

wherein the low-pass filter comprises a resistance configured to assist in performing the low-pass filtering operation on the demodulated signal, and

wherein the amplifier is further configured to amplify the input signal at a level of gain that is determined at least in part by a resistance value of the resistance of the low-pass filter.

10. The sensing device of claim 9,

wherein the low-pass filter further comprises a capacitance, and

wherein the low-pass filter is further configured to perform the low-pass filtering operation on the demodulated signal with a corner frequency determined at least in part by the resistance value of the resistance and a capacitance value of the capacitance.

11. The sensing device of claim 9, wherein the resistance of the low-pass filter is further configured to perform a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

12. The sensing device of claim 8,

wherein the low-pass filter comprises a resistance configured to assist in performing the low-pass filtering operation on the demodulated signal, and

wherein the resistance is further configured to perform a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

13. A biological impedance sensing device comprising:

means for applying a current modulated at a modulation frequency across a biological load to produce an input signal;

means for amplifying the input signal to produce an amplified signal;

means for demodulating the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load;

first implantable electrodes coupled to apply the modulated current across the biological load; and

second implantable electrodes coupled to sense the input signal produced across the biological load.

14. The sensing device of claim 13, further comprising:

means for modulating the output signal at the modulation frequency to produce a feedback signal; and

means for applying the feedback signal to the input signal.

15. The sensing device of claim 13, wherein the means for applying the modulated current comprises a voltage source and a switch that modulates a current produced by the voltage source to produce the modulated current.

16. The device of claim 13, wherein the means for demodulating the amplified signal comprises means for demodulating an amplitude of the amplified signal at the modulation frequency to produce a demodulated signal, and wherein the device further comprises means for performing a low-pass filtering operation on the demodulated signal to produce the output signal indicating an impedance of the biological load.

17. The sensing device of claim 16,

wherein the means for performing the low-pass filtering operation on the demodulated signal comprises means for performing, with at least a resistance, the low-pass filtering operation on the demodulated signal, and

wherein the means for amplifying the input signal comprises means for amplifying the input signal at a level of gain that is determined at least in part by a resistance value of the resistance.

18. The sensing device of claim 17, wherein the means for performing the low-pass filtering operation on the demodulated signal further comprises means for performing, with the resistance and a capacitance, the low-pass filtering operation on the demodulated signal with a corner frequency determined at least in part by the resistance value of the resistance and a capacitance value of the capacitance.

19. The sensing device of claim 17, further comprising:

means for performing, with at least the resistance, a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

20. The sensing device of claim 16, wherein the means for performing the low-pass filtering operation on the demodulated signal comprises:

means for performing, with at least a resistance, the low-pass filtering operation on the demodulated signal; and

means for performing, with at least the resistance, a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

21. The sensing device of claim 13,

wherein the amplified signal is a current-mode signal, and

wherein the means for demodulating the amplified signal comprises:

means for demodulating an amplitude of the amplified signal at the modulation frequency to produce a current-mode demodulated signal; and

means for performing a current-to-voltage conversion operation on the current-mode demodulated signal to produce a voltage-mode output signal indicating the impedance of the biological load.

22. The sensing device of claim 21,

wherein the means for amplifying the input signal comprises means for amplifying the input signal at a level of gain that is determined at least in part by a resistance value of a resistance, and

wherein the means for performing the current-to-voltage conversion operation comprises means for performing, with at least the resistance, the current-to-voltage conversion operation on the current-mode demodulated signal to produce the voltage-mode output signal.

23. The sensing device of claim 13, wherein the means for amplifying the input signal comprises:

means for amplifying the input signal at a level of gain that is determined at least in part by a resistance value of a resistance coupled between a node carrying the output signal and a node regulated at a common voltage.

24. The sensing device of claim 23, wherein the level of gain is determined at least in part by the resistance value of the resistance and a transconductance of a transconductor within the means for amplifying the input signal.

25. An implantable medical device comprising:

a therapy delivery module configured to deliver a therapy to a patient;

an impedance sensor comprising;

a current source configured to generate a modulated current at a modulation frequency for application across a biological load to produce an input signal,

an amplifier configured to amplify the input signal to produce an amplified signal,

a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load; and

a processor configured to control the therapy delivery module and process a representation of the output signal produced by the sensor.

26. The device of claim 25, wherein the impedance sensor further comprises:

a modulator configured to modulate the output signal at the modulation frequency to produce a feedback signal; and

a feedback path that applies the feedback signal to the input signal.

27. The device of claim 25,

wherein the demodulator is further configured to demodulate an amplitude of the amplified signal at the modulation frequency to produce a demodulated signal, and

wherein the impedance sensor further comprises a low-pass filter configured to perform a low-pass filtering operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

28. The device of claim 27,

wherein the low-pass filter comprises a resistance configured to assist in performing the low-pass filtering operation on the demodulated signal, and

wherein the amplifier is further configured to amplify the input signal at a level of gain that is determined at least in part by a resistance value of the resistance of the low-pass filter.

29. The device of claim 28,

wherein the low-pass filter further comprises a capacitance, and

wherein the low-pass filter is further configured to perform the low-pass filtering operation on the demodulated signal with a corner frequency determined at least in part by the resistance value of the resistance and a capacitance value of the capacitance.

30. The device of claim 28, wherein the resistance of the low-pass filter is further configured to perform a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

31. The device of claim 27,

wherein the low-pass filter comprises a resistance configured to assist in performing the low-pass filtering operation on the demodulated signal, and

wherein the resistance is further configured to perform a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

32. The device of claim 25,

wherein the impedance sensor further comprises a resistance coupled between a node carrying the output signal and a node regulated at a common voltage, and

wherein the amplifier is further configured to amplify the input signal at a level of gain that is determined at least in part by a resistance value of the resistance.

33. The device of claim 32,

wherein the amplifier comprises a transconductor, and

wherein the level of gain is determined at least in part by the resistance value of the resistance and a transconductance of the transconductor.

46. The device of claim 25, wherein the therapy delivery module comprises an electrical stimulation delivery module.

47. The device of claim 25, wherein the therapy delivery module comprises a fluid delivery module.

34. A method for sensing impedance of a biological load, the method comprising:

applying a current modulated at a modulation frequency across the biological load to produce an input signal;

amplifying the input signal with an amplifier to produce an amplified signal;

demodulating the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load;

applying the modulated current across the biological load via first implantable electrodes; and

sensing the input signal produced across the biological load via second implantable electrodes.

35. The method of claim 34, further comprising:

modulating an amplitude of the output signal at the modulation frequency to produce a feedback signal; and

applying the feedback signal to the input signal via a feedback path.

36. The method of claim 34, further comprising switching a current produced by a voltage source at the modulation frequency to produce the modulated current.

37. The method of claim 34, wherein demodulating the amplified signal comprises demodulating an amplitude of the amplified signal at the modulation frequency to produce a demodulated signal, the method further comprising performing a low-pass filtering operation on the demodulated signal to produce the output signal indicating an impedance of the biological load.

38. The method of claim 37,

wherein performing the low-pass filtering operation on the demodulated signal comprises performing, with at least a resistance, the low-pass filtering operation on the demodulated signal, and

wherein amplifying the input signal with the amplifier comprises amplifying the input signal at a level of gain that is determined at least in part by a resistance value of the resistance.

39. The method of claim 38, wherein performing the low-pass filtering operation on the demodulated signal further comprises performing, with the resistance and a capacitance, the low-pass filtering operation on the demodulated signal with a corner frequency determined at least in part by the resistance value of the resistance and a capacitance value of the capacitance.

40. The method of claim 38, further comprising:

performing, with at least the resistance, a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

41. The method of claim 37, wherein performing the low-pass filtering operation on the demodulated signal comprises:

performing, with at least a resistance, the low-pass filtering operation on the demodulated signal; and

performing, with at least the resistance, a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

42. The method of claim 34,

wherein the amplified signal is a current-mode signal, and

wherein demodulating the amplified signal comprises:

demodulating an amplitude of the amplified signal at the modulation frequency to produce a current-mode demodulated signal; and

performing a current-to-voltage conversion operation on the current-mode demodulated signal to produce a voltage-mode output signal indicating the impedance of the biological load.

43. The method of claim 42,

wherein amplifying the input signal with the amplifier comprises amplifying the input signal at a level of gain that is determined at least in part by a resistance value of a resistance, and

wherein performing the current-to-voltage conversion operation comprises performing, with at least the resistance, the current-to-voltage conversion operation on the current-mode demodulated signal to produce the voltage-mode output signal.

44. The method of claim 34, wherein amplifying the input signal with the amplifier comprises:

amplifying the input signal at a level of gain that is determined at least in part by a resistance value of a resistance coupled between a node carrying the output signal and a common node.

45. The method of claim 44, wherein the level of gain is determined at least in part by the resistance value of the resistance and a transconductance of a transconductor within the amplifier.

48. An electrical impedance sensing device comprising:

a current source configured to generate a modulated current at a modulation frequency for application to a load to produce an input signal, wherein the current source comprises a voltage source and a switch that modulates a current produced by the voltage source to produce the modulated current;

an amplifier configured to amplify the input signal to produce an amplified signal; and

a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load.

49. An electrical impedance sensing device comprising:

a current source configured to generate a modulated current at a modulation frequency for application to a load to produce an input signal;

an amplifier configured to amplify the input signal to produce an amplified signal, wherein the amplified signal is a current-mode signal;

a demodulator configured to demodulate an amplitude of the amplified signal at the modulation frequency to produce a current-mode demodulated signal; and

a current-to-voltage converter configured to perform a current-to-voltage conversion operation on the demodulated signal to produce a voltage-mode output signal indicating an impedance of the load.

50. An electrical impedance sensing device comprising:

a current source configured to generate a modulated current at a modulation frequency for application to a load to produce an input signal;

an amplifier configured to amplify the input signal to produce an amplified signal;

a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load; and

a resistance coupled between a node carrying the output signal and a node regulated at a common voltage,

wherein the amplifier is configured to amplify the input signal at a level of gain that is determined at least in part by a resistance value of the resistance to produce the amplified signal.

51. A biological impedance sensing device comprising:

means for applying a current modulated at a modulation frequency across a load to produce an input signal;

means for amplifying the input signal to produce an amplified signal; and

means for demodulating the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load,

wherein the means for amplifying the input signal comprises means for amplifying the input signal at a level of gain that is determined at least in part by a resistance value of a resistance coupled between a node carrying the output signal and a node regulated at a common voltage.

52. A method for sensing impedance of a load, the method comprising:

applying a current modulated at a modulation frequency across the load to produce an input signal;

amplifying the input signal with an amplifier to produce an amplified signal; and

demodulating the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load,

wherein amplifying the input signal with the amplifier comprises amplifying the input signal at a level of gain that is determined at least in part by a resistance value of a resistance coupled between a node carrying the output signal and a common node.