Blood monitoring apparatus and methods with amplifier input dark current correction
First Claim
Patent Images
1. Apparatus for monitoring a parameter of the blood in a body structure comprising:
- (a) photodetector means for producing a photodetector output signal related to the amount of light impinging upon said photodetector means;
(b) preamplification means having an input node for providing an amplified signal related to a signal supplied to said input node, said input node being connected to to said photodetector means for receipt of said photodetector output signal;
(c) illumination means for emitting light and directing the emitted light through the body structure so that emitted light transmitted through said body structure will impinge upon said photodetector means;
(d) means for periodically interrupting operation of said illumination means to provide dark intervals, whereby the photodetector output signal during each said dark interval will be a dark interval photodetector output indicative of ambient light impinging on said photodetector means;
(e) correction means for applying to said input node of said preamplification means a correction signal substantially equal in magnitude but opposite in sense to the dark interval photodetector output signal whereby said amplified signal will be substantially corrected for the effects of ambient light on said photodetector means; and
(f) interpretation means for determining said parameter of the blood from said corrected, amplified signal.
3 Assignments
0 Petitions
Accused Products
Abstract
In photoelectric apparatus such as a pulse oximeter for monitoring a parameter of the blood in a living organism, a dark current correction signal is applied to the input at the preamplifier. The correction signal is substantially equal in magnitude but opposite in sense to the photodetector output during dark intervals when the illumination means of the apparatus is disabled. Because dark current correction is accomplished at the input of the preamplifier, the preamplifier has substantially increased resistance to overloading caused by ambient light and hence may have higher gain.
293 Citations
14 Claims
-
1. Apparatus for monitoring a parameter of the blood in a body structure comprising:
-
(a) photodetector means for producing a photodetector output signal related to the amount of light impinging upon said photodetector means; (b) preamplification means having an input node for providing an amplified signal related to a signal supplied to said input node, said input node being connected to to said photodetector means for receipt of said photodetector output signal; (c) illumination means for emitting light and directing the emitted light through the body structure so that emitted light transmitted through said body structure will impinge upon said photodetector means; (d) means for periodically interrupting operation of said illumination means to provide dark intervals, whereby the photodetector output signal during each said dark interval will be a dark interval photodetector output indicative of ambient light impinging on said photodetector means; (e) correction means for applying to said input node of said preamplification means a correction signal substantially equal in magnitude but opposite in sense to the dark interval photodetector output signal whereby said amplified signal will be substantially corrected for the effects of ambient light on said photodetector means; and (f) interpretation means for determining said parameter of the blood from said corrected, amplified signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
-
-
14. A method of monitoring a parameter of the blood in a body structure comprising the steps of:
-
(a) producing a photodetector output signal related to the amount of light impinging upon a photodetector means and providing said photodetector output signal to an input of a preamplifier; (b) amplifying the signal applied to said input of said preamplifier so as to provide an amplified signal; (c) illuminating the body structure by emitting light and directing the emitted light through the body structure so that emitted light transmitted through said body structure impinges upon said photodetector; (d) periodically interrupting said illuminating step to provide dark intervals, whereby the photodetector output signal during each said dark interval will be a dark interval photodetector output indicative of ambient light impinging on said photodetector means; and (e) subtracting a correction signal from said photodetector output signal before said photodetector output signal is amplified in step (b), the magnitude of said correction signal being substantially equal to the magnitude of said dark interval photodetector output signal, whereby said amplified signal will be substantially corrected for the effect of ambient light; and (f) determining said parameter of the blood from said corrected amplified signal.
-
Specification