| 摘要 |
<p>An improved method and apparatus is disclosed for use in frequency division multiplexed spectrophotometric systems. The invention provides for the modulation of a plurality of light sources at different frequencies and in accordance with a predetermined phase relationship. Light from the sources (12a, 12b) that is transmitted through a tissue under test is detected at a detector (20). A composite signal indicative of the intensity of light received at the detector (20) is demodulated based on the different modulation frequencies and predetermined phase relationship to obtain signal portions corresponding with each of the light sources (12a, 12b). The modulation waveforms used to modulate the light sources (12a, 12b) and corresponding demodulation waveforms used to demultiplex the composite signal are symmetrically timed about a center point for each of the measurement periods. The invention reduces artifacts associated with rising/falling light source amplitude levels, thereby reducing system noise sentivity.</p> |
