Feedback-controlled LED switching

• US 6,825,619 B2
• Filed: 08/08/2002
• Issued: 11/30/2004
• 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.
• Primary Examiner(s): Lee, Wilson
• Assistant Examiner(s): Alemu, Ephrem
• Application Number:
  US10/215,878
• Publication Number:
  US 20040030229A1
• Time in Patent Office: 845 Days
• Field of Search: 315/149, 315/151, 315/291, 315/307, 600/323, 600/310, 356/41, 372/38.02, 372/38.07
• US Class Current: 315/149
• 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, said feedback controlled switch including an op-amp and a control switch having a first switching state where a first output of the op-amp is used to regulate a current passing through the diode and a second state where said control switch controls an output of said op-amp such that said diode is caused to be switched off.

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

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

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

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

9. The 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. The 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. The oximetry as claimed in claim 1, further comprising a current-changing device for varying a drive current to the diode.

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

24. The oximetry 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, said feedback controlled switch including an amplifier and a control switch having a first switching state where a first output of the amplifier is used to regulate a current passing through the diode and a second state where said control switch controls an output of said amplifier such that said diode is caused to be switched off.

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

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

14. The oximeter as claimed in claim 11, wherein the feedback-controlled switch comprises said amplifier, a control switch, and a plurality of transistors corresponding to the plurality of diodes.

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

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

17. The 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. The 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. The 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 amplifier and to a second one of the plurality of switch outputs.

20. The 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. The 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 between an output loop of the converter and a first input of said converter;

an unswitched reference voltage source directly connected to a second input of the voltage-to-current converter different than the first input; 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. The 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. The 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. The 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, where the switch switches current through the diode between on and off.