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AFE4490SPO2EVM: AFE4410EVM

barry dixon
Prodigy 40 points

Part Number: AFE4490SPO2EVM

Hi TI

We are using the AFE 4490 to develop another novel application  of pulse oximetry. 

We wish to maximise the signal processing capacity available in the software. 

In the documentation it states that the ambient DAC can be adjusted in 1uA to allow the DC signal to be near  the midpoint of the amplifier  0.9V.

My question is this voltage the voltage represented by the photodetector outputs seen on the LED 1 and LED 2 PPG traces.

Many thanks

Barry 

  • 0
    TI__Guru 50036 points

    Hello Barry,

    I apologize for the delay in my response.

    The photodiode (PD) is set to zero bias with the INP and INM pins biased to 0.9V.

    The voltage seen on the LED1 and LED2 PPG signals correspond to the PD current gained up by the trans-impedance amplifier.

    PPG signal typically consists of a large DC component and a very small AC component.

    The purpose of the ambient DAC is to reduce the DC signal so that the PPG signal can be centered near 0V.