Hi TI staff,
The oximeter I am making currently uses the AFE4404, and I have set up a calibration routine which maximises the pleth signal with the DAC offset and Amplifier gains. Since the DC level is very important to calculate SPO2, the offset is added back on in software using the appropriate datasheet DAC current and amplifier resistor. This works okay, but errors caused by the 20% DAC tolerance are affecting results.
In the datasheet I discovered the PD_DISCONNECT mode. From my understanding this allows us to measure the front end DAC/amplifier system independently, and give us an accurate DC value to add back on in software. I thought this would be a great way to account for device to device variation, but I'm running into a simple problem. For the larger DAC offsets and gains, this completely saturates the ADC. Am I misunderstanding how this mode work?
To be clear, a large gain and offset aren't an issue if they match the biological signal, but accurately measuring them seems impossible. Is this a common problem? How do you recommend working around this?
Thank you for your help,
Michael
