Active interference-noise cancellation device, and a method in relation thereto

1. An active noise cancellation device for a medical device, comprising:

an active circuit having a first input connection, a second input connection, and an output connection, wherein said second input connection is connected to at least one predetermined reference signal;

a low-impedance body connection electrode adapted to be in electrical contact with a bloodstream of a subject, wherein the low-impedance body connection electrode is connected to said first input connection; and

a feedback branch connecting the output connection with the first input connection;

wherein said feedback branch comprises a current limiting circuit adapted to limit a current through said feedback branch to be lower than a predetermined current.

2. The active noise cancellation device according to claim 1 , wherein said current is limited to be 50 μA or lower.

3. The active noise cancellation device according to claim 1 , wherein said active noise cancellation device is adapted to reduce the influence of an interference frequency of 50-60 Hz.

4. The active noise cancellation device according to claim 1 , wherein said at least one predetermined reference signal is a fixed reference voltage related to a ground of the medical device.

5. The active noise cancellation device according to claim 1 , wherein said at least one predetermined reference signal is related to a sensor signal of said medical device.

6. The active noise cancellation device according to claim 1 , wherein said at least one predetermined reference signal is obtained by switching between different sensor signals of said medical device.

7. The active noise cancellation device according to claim 1 , wherein said body connection electrode is adapted to be in direct connection to the bloodstream of the subject.

8. The active noise cancellation device according to claim 1 , wherein said current limiting circuit includes an impedance circuit.

9. The active noise cancellation device according to claim 1 , wherein said current limiting circuit includes a resistor unit.

10. The active noise cancellation device according to claim 1 , wherein said current limiting circuit includes a capacitance unit.

11. The active noise cancellation device according to claim 1 , wherein said medical device is a sensor guide wire, and said body connection electrode is adapted to be connected to an outer non-insulated tubing of said sensor guide wire.

12. The active noise cancellation device according to claim 1 , wherein said medical device is an elongated medical tube adapted to be inserted into the subject, and said noise cancellation device is arranged on a sensor chip at a distal end portion of said medical device.

13. The active noise cancellation device according to claim 12 , wherein said elongated medical tube is a sensor guide wire provided with a pressure sensor at the distal end portion.

14. A sensor guide wire comprising the active noise cancellation device according to claim 1 .

15. A method of active noise and interference cancellation in a medical device, comprising:

providing an active circuit having a first input connection, a second input connection, and an output connection, wherein said second input connection is connected to at least one predetermined reference signal,

arranging a low-impedance body connection electrode in electrical contact with a bloodstream of a subject, wherein said body connection electrode is connected to said first input connection,

providing a feedback branch connecting said output connection with said first input connection, and

limiting an error correction current through said feedback branch by providing a current limiting circuit such that said error correction current is lower than a predetermined current.

16. The method according to claim 15 , wherein the step of providing an active circuit includes providing an operational amplifier unit.

17. The method according to claim 15 , wherein said error correction current is limited to be 50 μA or lower.

18. The method according to claim 15 , wherein said active noise and interference cancellation is adapted to reduce the influence of an interference frequency of 50-60 Hz.

19. The method according to claim 15 , wherein said at least one predetermined reference signal is a fixed reference voltage related to a ground of the medical device.

20. The method according to claim 15 , wherein said at least one predetermined reference signal is related to a sensor signal of said medical device.

21. The method according to claim 15 , wherein said at least one predetermined reference signal is obtained by switching between different sensor signals of said medical device.

22. The method according to claim 15 , wherein said body connection electrode is adapted to be in direct connection to the blood of the subject.

23. The method according to claim 15 , wherein said current limiting circuit includes an impedance circuit.

24. The method according to claim 15 , wherein said current limiting circuit includes a resistor unit.

25. The method according to claim 15 , wherein said current limiting circuit includes a capacitance unit.

26. A medical device comprising:

an active noise cancellation device comprising:

an active circuit having a first input connection, a second input connection, and an output connection, wherein said second input connection is configured to be connected to at least one reference signal;

a low-impedance body connection electrode adapted to be in electrical contact with a bloodstream of a subject, wherein the low-impedance body connection electrode is connected to said first input connection; and

a feedback branch connecting the output connection with the first input connection;

wherein said feedback branch comprises a current limiting circuit configured to limit a current through said feedback branch to be lower than a predetermined current.