Abstract: The present invention is directed to a method and system for the determination of a spectral characteristic of light signals emitted by light signal emitters of a photoplethysmographic probe to achieve improved accuracy in photoplethysmographic blood analyte level determinations. In one embodiment, a system for use in photoplethysmography includes a plurality of light signal emitters (20A-D) within a photoplethysmographic probe (12) and a voltage sensor (60) and data processor (70) within a photoplethysmographic monitor unit (14) to which the probe (12) is connectable. The voltage sensor (60) is operable to sense a voltage drop across each light signal emitter (20A-D) as each emits a corresponding light signal (22A-D) for transmission through a tissue under test. The data processor (70) is operable to establish at least one spectral characteristic, such as the center wavelength, of each emitted light signal (22A-D) based on the sensed voltage drops.

Abstract: The present invention discloses a photoplethysmographic measurement apparatus and related method for determining a blood analyte level in a tissue under test employing an inventive laser diode drive scheme to achieve noise reduction. Noise reduction is achieved by driving a plurality of laser diodes with modulated drive signals to cause emission of light signals from the laser diodes that are directed through the tissue under test and from which various blood analyte levels are determinable based upon the intensities of the transmitted light signals. Each drive signal is modulated at an appropriate modulation frequency that causes its corresponding laser diode to operate in a low noise regime wherein laser intensity noise is reduced, and the modulation depth of each drive signal is set to broaden the line width of the laser diode and thereby reduce the potential for optical feedback noise.