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AFE4404EVM: Optimum parameter selection

RAHELEH MOHAMMADI
Prodigy 20 points

Part Number: AFE4404EVM
Other Parts Discussed in Thread: AFE4404,

Hi, 

we plan to use AfE4404 for our new product. we are going to use green LED for PPG signal acquisition. thepurpose is the get a clean Pulsatile signal. I was wondering how I can find the optimum LED current /TIA gain and offDAC parameter in a way that from subjectto subject and in different ambient light and also different skin tone or skin characteristic we still get the best PPG signal? I calculate SNR , Perfusion index and Dynamic range utilisation for lots of different combinations. now how I can decide which combination is going to work the best in all difefernt situations? 

kind Regards

 

  • 0
    TI__Expert 3560 points

    Hello Raheleh,

    The optimum LED current/TIA gain/Offset DAC parameters are going to depend on the specific LEDs/PDs you use, as well as the exact application for your system. In general, we recommend trying to maximize the total signal from the LEDs/PDs without saturating the signal chain. Since the TIA's full-scale range is 1V, make sure that whatever current/gain/DAC settings you choose will not exceed that 1V threshold. Beyond that recommendation, you will use your own tests to know exactly what settings will accomplish that best in different environments.

    Regards,

    Payton

  • 0 in reply to Payton Schubel
    Prodigy 20 points

    Hi Payton, 

    Many thanks for your quick reply. I am recording data from Toe using green LED. I found a combination based on your suggestion that gives me the signal below 1 volt and has a good range of SNR.  I tune the parameters and get a good result based on the data I recorded from my own Toe using AFE4404EVM board. now How I can make sure this will be working for a new person? Do you I need to have any automatic gain change or calibration routine at the beginning of recording for new patient? 

    In general could you please let me know what is the purpose of calibration routine ? how often should it be done ?

    Many thanks in advance 

    Raheleh 

  • 0 in reply to RAHELEH MOHAMMADI
    TI__Expert 3560 points

    Hi Raheleh,

    While TI recommends a calibration routine when signal conditions change, we do not provide the algorithm. You will need to decide how to calibrate the device based on the requirements for your system.

    In general, TI recommends a calibration loop when the signal conditions change in order to account for differences in offset/magnitude/etc. that come from a new subject. Tuning LED Current/gain/offset/bandwidth will help you best utilize that dynamic range for a new person. However, the exact manner you choose to perform that calibration is up to you.

    Regards,

    Payton

  • 0 in reply to Payton Schubel
    Prodigy 20 points

    Hi Payton, 

    Many thanks for your reply. I found something about calibration here : AFE4404: How to write AFE 4404 Offset Calibration routine - Sensors forum - Sensors - TI E2E support forums. 

    I could not find the mentioned document in this post.  Could you please explain what does this calibration routine does? is it possible to share this document?

    Kind Regards

    Raheleh 

  • 0 in reply to RAHELEH MOHAMMADI
    TI__Expert 3560 points

    Hello Raheleh,

    The AFE4404 Calibration Conceptual Visualization can be found with the resources for the AFE4404EVM Board.

    Once on the page, download the firmware source circled below, and run the installer.

    Once the installer has been run, you can find the calibration visualization at the C:\AFE4404EVMFWSRC-v1.4\AFE4404EVM_FW_SRC-1.4_release\Documents\AFE4404_Calibration_Conceptual Visualization.pdf file location mentioned in that previous post.

    Regards,

    Payton

  • 0 in reply to Payton Schubel
    Prodigy 20 points

    Hi Payton, 

    Many thanks for your guidance. Just found the document. Now Is it possible to use this calibration routine ( mentioned in this document) at the beginning of each recording (when the condition changes) in the final product? In the AFE4404 EVM GUI software,  inside "ADC Capture &Analysis" tab , there is " Enable Calibration Routine? " . Is this connected to the above document? 

    Kind Regards

    Raheleh 

  • 0 in reply to RAHELEH MOHAMMADI
    TI__Expert 3560 points

    Hi Raheleh,

    Yes, you can use the calibration routine at the beginning of each recording when the condition changes. Enabling the calibration routine in the GUI will also perform this calibration.

    Regards,

    Payton