Direct digital capture of pulse oximetry waveforms

Pulse oximetry sensor photodiodes typically generate a current proportional to the intensity of the pulse oximetry waveforms. This method of waveform capture is prone to electrical noise and requires analog-to-digital conversion downstream for further digital signal processing. This investigation evaluated the use of a light-to-frequency photodiode as an alternative sensor for capturing pulse oximetry waveforms. Red and infrared pulse oximetry waveforms were captured with a Texas Instruments TSL220 light-to-frequency converter. The fidelity of the captured waveforms was excellent. The compact TSL220 combination of photodiode, amplifier, and current-to-frequency converter can potentially replace the light-to-current photodiode, current-to-voltage converter, and analog-to-digital converter now used in typical pulse oximetry applications.