Synchronized modulation/demodulation method and apparatus for frequency division multiplexed spectrophotometric system
US6363269B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | Dec 17, 1999 |
| Grant date | Mar 26, 2002 |
| Priority date | — |
| Expiry date | Dec 17, 2019 |
Classification
- Technology area (CPC A)Human Necessities
- CPC primaryA61B5/14551
- WIPO fieldMedical technology
- WIPO sectorInstruments
Abstract
An improved method and apparatus is disclosed for use in frequency division multiplexed spectrophotometric systems. In photoplethysmographic applications 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 that is transmitted through a tissue under test is detected at a detector. A composite signal indicative of the intensity of light received at the detector is demodulated based on the different modulation frequencies and predetermined phase relationship to obtain signal portions corresponding with each of the light sources. Modulation and demodulation are synchronized during each measurement period. The modulation waveforms used to modulate the light sources 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 sensitivity.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.