Calculation of oxygen saturation and heartrate measurement in AFE4490

Stefan,

AFE4490 datasheet and AFE4490SPO2EVM Users Guide are the related documents that you are looking for.

They are publicly available at the TI website.

Please refer to the following links:

Datasheet: http://www.ti.com/product/afe4490

EVM User'sGuide: http://www.ti.com/tool/afe4490spo2evm

The EVM User's Guide contains the schematics of the EVM.

The datasheet provides details of how the LEDs are connected to the LED_DRV_SUP in the two modes H-Bridge and Push Pull drive. Refer to the Transmit section.

Refer to the Receiver Channel section for details about the filters on the AFE.

AFE4490 integrates a completely configurable timer module. This timer module offers programmability and flexibility in controlling the various timing edges for sampling and conversion of LEDs and ambient phases.

Earlier today I sent a document to your email address that outlines the calculation of SpO2 using PPG signals. Figure 2 of that document shows what the DC measurement refers to on the PPG signals.  SpO2 estimation is based on computing the “ratio of ratios” or Pulse Modulation ratio R which is defined as the ratio of AC/DC of red and IR LEDs.

Since the light absorption of the oxygenated and deoxygenated haemoglobin of blood is significantly wavelength-dependent, the relationship between R and SpO2 strongly depends on the specific emission characteristics of the sensor’s LEDs. Accurate measurements of saturation require the sensor's calibration curve.