Laser diode drive scheme for noise reduction in photoplethysmographic measurements

摘要

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. In this regard, the modulation frequency and depth of each drive signal may be set to achieve operation of its corresponding laser diode at a desired laser intensity noise level. The desired laser intensity noise level may be near that (e.g., within the same order of magnitude) of the independent laser RIN level.