Drive circuit for light-emitting diode in pulse oximeter

A drive circuit for use in a pulse oximeter for measuring a degree of oxygen saturation of arterial blood in a living tissue, said drive circuit comprising:

• at least two light emitting elements different in wavelength for irradiating said living tissue containing said arterial blood;
• a light receiving element for receiving light irradiated from said light emitting elements and traversing said living tissue directly and indirectly to said light receiving element;
• means for intermittently applying an inverse bias voltage across said light emitting elements;
• means including at least one inductor for applying an inverse electromotive voltage across said light emitting elements, said means for applying an inverse electromotive voltage being connected to said light emitting elements and to said means for intermittently applying an inverse bias voltage;
• and
• signal processing means which is capable of calculating a ratio of a change of light absorption of at least two wavelengths transmitted alternatively from said light emitting elements,
• wherein said ratio is based on signals output from said light receiving element and said ratio represents said degree of oxygen saturation of said arterial blood.