Blood oxygen sensor having leakage compensation
First Claim
1. A leakage compensation circuit for use in a blood oxygen sensor of the kind that includes a light-emitting diode for selectively illuminating the blood and a photosensor for sensing the intensity of light reflected by the blood, wherein the light-emitting diode has a capacitor and leakage resistance arranged in parallel with it, the leakage compensation circuit comprising:
- initialization means for supplying an initialization current during an initialization mode to controllably charge the capacitor arranged in parallel with the light-emitting diode to a predetermined voltage that is less than an onset voltage at which the light-emitting diode emits substantial light, wherein the initialization means includes means for controllably increasing the initialization current with time, to compensate for the presence of the leakage resistance in parallel with the capacitor; and
pulse means for supplying a light-generating current to the light-emitting diode during a measurement mode, which follows the initialization mode, the light-generating current being substantially greater than the initialization current, such that the light-emitting diode emits substantial light for reflection by the blood and sensing by the photosensor;
wherein the charging of the capacitor to the predetermined voltage during the initialization mode facilitates the emission by the light-emitting diode of a more well-defined amount of light and the generation by the sensor of an accurate measurement of blood oxygen saturation.
3 Assignments
0 Petitions
Accused Products
Abstract
An improved blood oxygen sensor apparatus having a special leakage compensation circuit that allows proper initialization of the oxygen sensor regardless or the value of leakage resistance which typically might be present in parallel with the oxygen sensor. During an initialization mode, in which a capacitor arranged in parallel with oxygen sensor is charged by a small initialization current, the leakage compensation circuit monitors the capacitor voltage and controllably increases the current if it is determined that the capacitor is charging at an insufficient rate, due to unspecified leakage resistance. This enables the oxygen sensor to be properly initialized such that it can thereafter accurately measure blood oxygen levels.
-
Citations
35 Claims
-
1. A leakage compensation circuit for use in a blood oxygen sensor of the kind that includes a light-emitting diode for selectively illuminating the blood and a photosensor for sensing the intensity of light reflected by the blood, wherein the light-emitting diode has a capacitor and leakage resistance arranged in parallel with it, the leakage compensation circuit comprising:
-
initialization means for supplying an initialization current during an initialization mode to controllably charge the capacitor arranged in parallel with the light-emitting diode to a predetermined voltage that is less than an onset voltage at which the light-emitting diode emits substantial light, wherein the initialization means includes means for controllably increasing the initialization current with time, to compensate for the presence of the leakage resistance in parallel with the capacitor; and pulse means for supplying a light-generating current to the light-emitting diode during a measurement mode, which follows the initialization mode, the light-generating current being substantially greater than the initialization current, such that the light-emitting diode emits substantial light for reflection by the blood and sensing by the photosensor; wherein the charging of the capacitor to the predetermined voltage during the initialization mode facilitates the emission by the light-emitting diode of a more well-defined amount of light and the generation by the sensor of an accurate measurement of blood oxygen saturation. - View Dependent Claims (2, 3, 4, 5, 6, 7)
-
-
8. A blood oxygen sensor apparatus for use with a pacemaker, comprising:
-
a light-emitting diode positioned such that its emitted light is directed at blood whose oxygen saturation level is to be measured, wherein a capacitor and leakage resistance are arranged in parallel with the light-emitting diode; a photodetector positioned to detect light emitted by the light-emitting diode and reflected by the blood and to produce a corresponding intensity signal; detection means responsive to the intensity signal, for determining the blood'"'"'s oxygen content; and initialization means for supplying an initialization current during an initialization mode to charge the capacitor substantially linearly to a predetermined voltage that is less than an onset voltage at which the light-emitting diode emits substantial light, wherein the initialization means includes means for controllably increasing the initialization current with time, to compensate for the presence of the leakage resistance, and wherein the charging of the capacitor to the predetermined voltage during the initialization mode facilitates the emission by the light-emitting diode of a well-defined amount of light and the generation by the apparatus of an accurate measurement of blood oxygen saturation and means for driving said LED. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
-
-
24. A method for use with a heart pacemaker in sensing blood oxygen content, comprising steps of:
-
positioning a light-emitting diode such that its emitted light is directed at blood whose oxygen saturation level is to be measured, and a capacitor in parallel with the light-emitting diode, with leakage resistance also being arranged in parallel with the capacitor; positioning a photodetector so as to detect light emitted by the light-emitting diode and reflected by the blood, thereby producing a corresponding intensity signal; monitoring the intensity signal, to determine the blood'"'"'s oxygen content; and supplying an initialization current during an initialization mode to charge the capacitor to a predetermined voltage that is less than an onset voltage at which the light-emitting diode emits substantial light, wherein the step of supplying includes a step of controllably increasing the initialization current with time, to compensate for the presence of leakage resistance; wherein the charging of the capacitor to the predetermined voltage in the step of supplying facilitates the emission by the light-emitting diode of a well-defined amount of light and the generation in the step of monitoring of an accurate measurement of blood oxygen saturation. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31)
-
-
32. A blood oxygen content sensor apparatus for use with a pacemaker, comprising:
-
a light-emitting diode positioned such that its emitted light is directed at blood whose oxygen saturation level is to be measured, wherein a capacitor and leakage resistance are arranged in parallel with the light-emitting diode, the leakage resistance having a non-predetermined value within a predetermined range; a phototransistor positioned to detect light emitted by the light-emitting diode and reflected by the blood and to produce a corresponding intensity signal; detection means responsive to the intensity signal, for determining the blood'"'"'s oxygen content; initialization means for supplying an initialization current to the light-emitting diode during an initialization mode, to charge the capacitor substantially linearly to a predetermined voltage substantially the same as, but slightly less than, an onset voltage at which the light-emitting diode emits substantial light; and pulse means for supplying a light-generating current to the light-emitting diode during a measurement mode, following the initialization mode, the light-generating current being substantially greater than the initialization current, such that the light-emitting diode emits substantial light for reflection by the blood and sensing by the phototransistor; wherein the detection means includes; integrator means for integrating the intensity signal produced by the photodetector during the measurement mode, to produce an integrated intensity signal, comparator means for comparing the integrated voltage signal with a predetermined threshold and, when the integrated voltage signal reaches the predetermined threshold, for accepting a substantial portion of the light-generating current supplied by the pulse means, thereby reducing the voltage applied to the light-emitting diode below the onset voltage, and means for monitoring the voltage applied to the light-emitting diode and for establishing a detection time when the voltage is reduced below the onset voltage, the time delay from initiation of the measurement mode until the detection time being inversely related to the blood'"'"'s oxygen saturation level; wherein the charging of the capacitor to the predetermined voltage during the initialization mode facilitates the emission by the light-emitting diode of a well-defined amount of light and the generation by the apparatus of an accurate measurement of blood oxygen content. - View Dependent Claims (33, 34, 35)
-
Specification