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LMH32404: TIA Circuit Compatibility w/ VEMD2023SLX01 Photodiode

Ezira Yimer Wolle
Prodigy 20 points
Part Number: LMH32404

Tool/software:

I'm currently designing a photodiode array circuit w/ 18 VEMD2023SLX01 (https://www.vishay.com/docs/83493/vemd2023slx01.pdf) photodiode components. Given limited pcb real estate and i/o pins, im interested in using the LMH32404 to easily amplify and multiplex data to downstream ADCs. I wanted to make sure that these are compatible with the photodiodes I'm working with (when applied with a 5V reverse voltage the datasheet indicates that the PD capacitance is 1.3pF and max current is 14uA, which makes me think at first glance it should be okay). Secondly, is it possible to use convert the outputs to single-ended rather than differential? Generally also interested in using ADCs on Arduino's, which do not accept differential inputs.

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    TI__Mastermind 23385 points

    Hello Ezira,

      I apologize for the very long delay in response. You are correct, there shouldn't be an issue with using your photodiode with this device.

      The datasheet does show around 1.3pF if you apply a 5V reverse voltage, which is similar to the conditions tested when characterizing the device. The bandwidth listed for the photodiode seems to be a few MHz, and the max current looks like is 14uA which would be fine with this device which has an integrated current noise in the few nAs. 

      This device can be used in either single or differential, but it is recommended for differential for optimal performance. In single-ended signal chains terminate the unused differential output in the same manner as the used output to maintain balance and symmetry. The signal swing of the single-ended output is half the available differential output swing. Additionally, the common-mode noise of the output stage, which is typically rejected by the differential input ADC, is now added to the total noise, further degrading SNR.

      If the ADC in the Arduino is differential input, it would be ideal; otherwise try to terminate the unused output with the same impedance as the output connected to the single-ended ADC to maintain symmetry to maintain common-mode performance. 

     Let me know by replying if you need more clarification of above!

    Thank you,
    Sima