SYSTEM AND CIRCUIT FOR DISTRIBUTION OF PRECISE CURRENTS TO NUMEROUS PATIENT ELECTRODES AND FOR NON-INVASIVE PATIENT-ELECTRODE VOLTAGE MEASUREMENTS

• US 20130102920A1
• Filed: 11/18/2010
• Published: 04/25/2013
• Est. Priority Date: 11/18/2009
• Status: Active Grant

• Current Assignee: ImpediMed Limited
• Original Assignee: ImpediMed Limited
• Inventors: Fan, Chung Shing, Ironstone, Joel, Smith, Kenneth Carless
• Granted Patent: US 9,585,593 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61B 5/4875 Hydration status, fluid retention of the body
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure
• CPC Class Codes: A61B 5/6885 Monitoring or controlling sensor contact pressure
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: G01R 1/30 Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00
• CPC Class Codes: G01R 31/00 Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere measuring superconductive properties G01R33/1238; testing or measuring semiconductors or solid state devices during manufacture H01L22/00; testing line transmission systems H04B3/46
• CPC Class Codes: H03F 2200/261 Amplifier which being suitable for instrumentation applications
• CPC Class Codes: H03F 3/50 Amplifiers in which input is applied to, or output is derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
• CPC Class Codes: H03F 3/602 Combinations of several amplifiers

Abstract

Apparatus for electrically connecting measurement apparatus to a biological subject, the apparatus including a signal delivery circuit including a current buffer having a current buffer input for receiving a signal from a signal source and a current buffer output for supplying a current to an electrode attached to the biological subject, and a voltage buffer having a voltage buffer input coupled to the current buffer output and a voltage buffer output for providing a voltage signal indicative of a voltage at the electrode, to a sensor.

Claims

1. Apparatus for electrically connecting measurement apparatus to a biological subject, the apparatus including a signal delivery circuit including:

a current buffer having;

a current buffer input for receiving a signal from a signal source; and

,

a current buffer output for supplying a current to an electrode attached to the biological subject; and

,

a voltage buffer having;

a voltage buffer input coupled to the current buffer output; and

,

a voltage buffer output for providing a voltage signal indicative of a voltage at the electrode, to a sensor.

2. Apparatus according to claim 1, wherein the current buffer is a current conveyor.

3. Apparatus according to claim 1, wherein the voltage buffer is an amplifier connected as an output follower.

4. Apparatus according to claim 1, wherein the apparatus includes an offset control circuit coupled between the voltage buffer output and the current buffer input.

5. Apparatus according to claim 4, wherein the offset control circuit includes an integrator coupled between the voltage buffer output and the current buffer input.

6. Apparatus according to claim 4, wherein the offset control circuit is used to control a DC offset at the electrode.

7. Apparatus according to claim 1, wherein the signal delivery circuit includes a negative impedance circuit coupled between the voltage buffer output and the current buffer output.

8. Apparatus according to claim 7, wherein the negative impedance circuit includes a negative impedance circuit amplifier and a compensation impedance.

9. Apparatus according to claim 8, wherein at least one of a gain of the negative impedance circuit amplifier and a value of the compensation impedance is selected to compensate for parasitic impedance losses.

10. Apparatus according to claim 7, wherein the negative impedance circuit includes:

a compensation impedance having a compensation impedance value, a first terminal and a second terminal, the first terminal coupled to the current buffer output; and

,

a compensation amplifier having a compensation amplifier input, a compensation amplifier output and a gain, the compensation amplifier input coupled to the voltage buffer output, the compensation amplifier output coupled to the second terminal of the compensation impedance to provide a compensation current to flow through the impedance, and the gain and the compensation impedance values are selected based on the parasitic impedance value so that the compensation current has a magnitude substantially equal to the leakage current magnitude.

11. Apparatus according to claim 1, wherein the apparatus includes:

a plurality of signal delivery circuits, each signal delivery circuit being for supplying a current to a respective electrode attached to the biological subject;

at least one signal source; and

,

at least one first multiplexer for selectively connecting the signal source to one of the plurality of signal delivery circuits to thereby apply a current to the biological circuit via the respective electrode.

12. Apparatus according to claim 1, wherein the apparatus includes:

a plurality of signal delivery circuits, each signal delivery circuit being for providing a voltage signal indicative of a voltage at the electrode, to a sensor;

at least one sensor; and

,

at least one second multiplexer for selectively connecting the at least one sensor to one of the plurality of signal delivery circuits to thereby allow the sensor to sense the voltage signal indicative of a voltage at the respective electrode.

13. Apparatus according to claim 1, wherein the apparatus includes, first and second signal sources for generating respective first and second drive signals, the first and second signal sources being coupled to respective signal delivery circuits.

14. Apparatus according to claim 13, wherein the first and second signal sources are for generating at least one of:

complementary signals;

signals having a constant amplitude and phase; and

,

signals having a controlled amplitude and phase.

15. Apparatus according to claim 1, wherein at least one signal source is coupled to ground.

16. Apparatus according to claim 1, wherein the apparatus includes:

at least one signal delivery circuit for supplying a current to a drive electrode attached to the biological subject; and

,

at least one signal delivery circuit for providing a voltage signal indicative of a voltage at a sense electrode.

17. Apparatus according to claim 1, wherein the measurement apparatus includes at least one signal source and at least one sensor.

18. Apparatus according to claim 17, wherein the measurement apparatus is an impedance measurement apparatus.

19. A current multiplexing system comprising:

a plurality of current multiplexers having at least one input and a plurality of outputs;

a first and second alternating-current current source each current source having a constant magnitude and frequency, wherein the second current source is complimentary to the first current source, each of the first and second current sources is coupled to an input of a current multiplexer;

a plurality of current delivery circuits, each current delivery circuit having an input, a current output and a voltage output, wherein each current delivery circuit input is coupled to an output of a current multiplexer;

a plurality of electrodes, each of the plurality of electrodes being coupled to a current output of one of the plurality of current delivery circuits; and

at least one voltage multiplexer having a plurality of inputs and at least one output;

wherein each current delivery circuit comprises;

a current conveyor, having an input and an output, the current conveyor input being coupled to the current delivery circuit input and the current conveyor output being coupled to the current delivery circuit current output;

a voltage buffer, having an input and an output, the voltage buffer input being coupled to the current delivery circuit current output and the voltage buffer output being coupled to the current delivery circuit voltage output;

an integrator coupled between the voltage buffer output and the current conveyor input; and

,

a negative impedance circuit coupled between the voltage buffer output and the current conveyor output, the negative impedance comprising;

a compensation impedance having a compensation impedance value, a first terminal and a second terminal, the first terminal coupled to the current conveyor output;

a compensation amplifier having a compensation amplifier input, a compensation amplifier output and a gain, the compensation amplifier input coupled to the voltage buffer output, the compensation amplifier output coupled to the second terminal of the compensation impedance to provide a compensation current to flow through the impedance, and the gain and the compensation impedance values are selected based on the parasitic impedance value so that the compensation current has a magnitude substantially equal to the leakage current magnitude.

20. Apparatus for electrically connecting measurement apparatus to a biological subject, the apparatus including a signal delivery circuit including:

a first buffer having;

a first buffer input for receiving a signal from a signal source; and

,

a first buffer output for supplying a drive signal to an electrode attached to the biological subject; and

,

a second buffer having;

a second buffer input coupled to the first buffer output; and

,

a second buffer output for providing a sensed signal indicative of a signal at the electrode, to a sensor.

21. Apparatus according to claim 20, wherein the first buffer is a current buffer, the drive signal being a drive current.

22. Apparatus according to claim 21, wherein the current buffer is a current conveyor.

23. Apparatus according to claim 20, wherein the second buffer is a voltage buffer the sensed signal being a voltage signal indicative of a voltage at the electrode.

24. Apparatus according to claim 20, wherein the second buffer is a current buffer the sensed signal being indicative of the drive current.

25. Apparatus for use in performing impedance measurements on a subject, wherein the apparatus includes:

a signal source for applying a signal to a subject;

a sensor for sensing signals from the subject;

a processing system for controlling the signal source and receiving signals from the sensor; and

,

at least one signal delivery circuit, including;

a first buffer having;

a first buffer input for receiving a signal from a signal source; and

,

a first buffer output for supplying a drive signal to an electrode attached to the biological subject; and

,

a second buffer having;

a second buffer input coupled to the first buffer output; and

,

a second buffer output for providing a sensed signal indicative of a signal at the electrode, to a sensor.

26. Apparatus according to claim 25, wherein the apparatus includes:

at least one signal delivery circuit for supplying a current to a drive electrode attached to the biological subject; and

,

at least one signal delivery circuit for providing a voltage signal indicative of a voltage at a sense electrode.

27. Apparatus according to claim 26, wherein the apparatus includes:

a first signal delivery circuit coupled to a drive electrode attached to the biological subject, the first signal delivery circuit including;

a first buffer having;

a first buffer input for receiving a signal from the signal source; and

,

a first buffer output for supplying the drive signal to the drive electrode; and

,

a second buffer having;

a second buffer input coupled to the first buffer output; and

,

a second buffer output for providing a sensed signal indicative of the drive signal at the drive electrode;

a second signal delivery circuit coupled to a sense electrode attached to the biological subject, the second signal delivery circuit including.

a first buffer having;

a first buffer input coupled to ground; and

,

a first buffer output coupled to the sense electrode; and

,

a second buffer having;

a second buffer input coupled to the first buffer output; and

,

a second buffer output for providing a sensed signal indicative of a sensed voltage at the sense electrode.