Feedback-controlled led switching

• US 20040030229A1
• Filed: 08/08/2002
• Published: 02/12/2004
• Est. Priority Date: 08/08/2002
• Status: Active Grant

• Current Assignee: Datex-Ohmeda Incorporated (General Electric Company)
• Original Assignee: Datex-Ohmeda Incorporated (General Electric Company)
• Inventors: Norris, Mark A.
• Granted Patent: US 6,825,619 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor

Abstract

An oximeter has an op-amp with a first input, a second input, and an output, the first input being directly connected to a reference voltage. A switch has an input connected to the output of the op-amp, and has a plurality of switch outputs. A transistor has a control input connected to one of the plurality of outputs, and has a current source terminal and a supply terminal. A diode is connected to the current source terminal of the transistor. The supply terminal of the transistor is connected both to the second input of the op-amp and to a second one of the plurality of switch outputs. The switch is thereby in a feedback loop of the op-amp, effecting a feedback-controlled switch for switching the diode on and off.

Claims

1. A pulse oximetry device that converts pulses into light flashes, comprising:

a diode for emitting the light flashes;

a current sense element for sensing at least a part of a current being supplied to the diode of the oximeter; and

a feedback-controlled switch for switching the diode on and off.

2. An oximetry device as claimed in claim 1, wherein the diode is an LED.

3. An oximetry device as claimed in claim 1, wherein the diode is a laser diode.

4. An oximetry device as claimed in claim 1, wherein the feedback-controlled switch comprises an op-amp, a control switch, and a transistor.

5. An oximetry device as claimed in claim 4, wherein the op-amp comprises a first input, a second input, and an output, the first input being directly connected to a reference voltage.

6. An oximetry device as claimed in claim 5, wherein the control switch comprises an input, connected to the output of the op-amp, and a plurality of switch outputs.

7. An oximetry device as claimed in claim 6, wherein the transistor comprises a control input, connected to one of the plurality of switch outputs, a current source terminal, and a supply terminal.

8. An oximetry device as claimed in claim 7, wherein the diode is connected to the current source terminal of the transistor.

9. An oximetry device as claimed in claim 8, wherein the supply terminal of the transistor is connected both to the second input of the op-amp and to a second one of the plurality of switch outputs.

10. An oximetry device as claimed in claim 4, wherein the transistor comprises one of a bipolar transistor, a field effect transistor, an insulated-gate semiconductor, and a semiconductor controlled rectifier.

21. An oximeter as claimed in claim 1, further comprising a current-changing device for varying a drive current to the diode.

22. An oximeter according to claim 21, wherein the current sensing element comprises a network of individual resistors that are adapted to be selectively connected in different series and/or parallel combinations.

23. An oximeter according to claim 22, further comprising low ohm transistors operative to perform a connecting of ones of the individual resistors.

24. An oximeter according to claim 21, wherein the current sensing element comprises a variable resistor.

11. A pulse oximeter that converts pulses into light flashes, comprising:

a plurality of diodes for emitting the light flashes;

a plurality of current sense elements corresponding to the plurality of diodes, for sensing at least a part of a current being supplied to each respective diode of the oximeter; and

a feedback-controlled switch for switching a selected one of the plurality of diodes on and off.

12. An oximeter as claimed in claim 11, wherein the plurality of diodes are LEDs.

13. An oximeter as claimed in claim 11, wherein the plurality of diodes are laser diodes.

14. An oximeter as claimed in claim 11, wherein the feedback-controlled switch comprises an op-amp, a control switch, and a plurality of transistors corresponding to the plurality of diodes.

15. An oximeter as claimed in claim 14, wherein the op-amp comprises a first input, a second input, and an output, the first input being directly connected to a reference voltage.

16. An oximeter as claimed in claim 15, wherein the control switch comprises a switch input connected to the output of the op-amp, and a plurality of switch outputs corresponding to the plurality of diodes.

17. An oximeter as claimed in claim 16, wherein each of the plurality of transistors comprises a control input, connected to a corresponding different one of the plurality of switch outputs, a current source terminal, and a supply terminal.

18. An oximeter as claimed in claim 17, wherein the each of the plurality of diodes is connected to the current source terminal of a corresponding one of the plurality of transistors.

19. An oximeter as claimed in claim 18, wherein the supply terminal of each of the plurality of transistors is connected both to the second input of the op-amp and to a second one of the plurality of switch outputs.

20. An oximeter as claimed in claim 14, wherein the plurality of transistors comprise one of bipolar transistors, field effect transistors, insulated-gate semiconductors, and semiconductor controlled rectifiers.

25. An oximeter as claimed in claim 11, further comprising a current-changing device for individually varying a plurality of drive currents corresponding to the plurality of diodes.

26. A current driving apparatus in an oximeter, comprising:

a voltage-to-current converter having a feedback loop;

an unswitched reference voltage source directly connected to an input of the voltage-to-current converter; and

a switch disposed in the feedback loop,

whereby the unswitched reference voltage source is isolated from the switch.

27. A method of driving a current through a diode in a pulse oximeter that converts pulses into light flashes, comprising:

connecting a feedback-controlled device to the diode of the pulse oximeter, the diode being for emitting the light flashes, the feedback-controlled device comprising a feedback loop having a switch;

switching on and off the diode by changing a switch position of the switch.

28. A method according to claim 27, further comprising changing a value of a current sensing resistor disposed in series with the diode, for changing a drive current to the diode.

29. A method according to claim 28, wherein the changing of the value of current sensing resistor is effected by selectively connecting individual resistors of a resistor network in different series/parallel combinations.

30. A method according to claim 27, further comprising modulating the current through the diode.

31. A method of using a switch for switching current through a light flash emitting diode of a pulse oximeter on or off, the method comprising:

sensing a current passing through a current path that includes the diode of the pulse oximeter;

directly connecting a reference voltage to an amplifier;

causing the amplifier to regulate the current passing through the current path according to the reference voltage and the sensed current; and

placing the switch in a feedback loop of the amplifier.

33. A method according to claim 31, further comprising directly supplying an unswitched reference voltage to the feedback amplifier in order to stabilize the current.

34. A method according to claim 31, further comprising modulating the current through the diode.

32. A method of on/off controlling a current through a diode of an oximeter, comprising switching an output of a feedback amplifier, in a feedback loop of the feedback amplifier.