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LMH6629: Looking for a solution to work in open sunlight environment with Photodiodes and Transimpedance amplifier.

Hardik Raval
Intellectual 270 points
Part Number: LMH6629
Other Parts Discussed in Thread: LMH34400, LMH32401, THVD8000

Tool/software:

Dear Tech Experts,

I am working on Gate Access Application using IR Light as a Transmitter and Photodiode as a receiver.

I am able to send digital data from the IR transmitter at 130KHz and working wavelength is 850nm.

My setup of Transmitter and Receiver is working in the Indoor Environment but not working in the open environment(in the open space, in the bright sunlight).

On the receiving end, i am using Photodiode(OSRAM SFH 213 FA, Vishay BPW85B, Hamamatsu S7478) Transimpedance Amplifier(LMH6629) and Comparator(MCP6V91T).

My observation with all photodiodes:

During day time, noon time and evening time, output of transimpedance amplifier changes its values and that affects to comparator as well.

I am not able to receive data. Mt be data is getting saturated.

Seeking for a solution, where i can receive perfect data in the bright sunlight as well.

Best Regards
Hardik Raval

  • 0
    TI__Genius 15681 points

    Hello Hardik,

    You may be experiencing an overload of the photodiode, such that the increased amount of light outdoors is saturating the photodiode.  This saturation amount may be dependent on the amount of light which contributes to different outputs from the PD + TIA circuit.

    There is a feature we have on some of our integrated TIA ICs known as ambient light cancellation.  This has been discussed before on the forum: https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/913347/cancellation-of-ambient-light

    You are likely encountering more ambient light outdoors than in your indoor (controlled) environment.

    There are methods for external circuitry around your TIA to cancel ambient light.  These methods are typically referred to as 'DC cancellation loops", as the ambient light is a DC source when compared to your AC data signal.  The LMH34400 and LMH32401/4 devices have ALC integrated.  For other TI TIAs, you will need to build a DC cancellation loop yourself, using a reference voltage, error amplifier and a voltage to current (V-to-I) converter.  There is a source on the web which briefly discusses this practice: DC Cancellation Loop.

    Best,

    Alec

  • 0
    TI__Prodigy 305 points

    Hi Hardik,

    We have developed a tool to design a TIA circuit with photodiode interface, Analog circuit design studio. Please try the tool to test your circuit, and let me know if you have any queries or doubts. You can use this tool to design a circuit by selecting an OpAmp, and other way is that you insert values of interest, and the tool will suggest an OpAmp for the given values. You can find LMH6629 in the drop down for designing the circuit.

    Thanks

    Aditya Gosavi

  • 0 in reply to Alec Saebeler
    Intellectual 270 points

    Thanks Alex
    I will try using ALC TIA. 
    For now i am transmitting data at 130KHz without modulation.
    Can you suggest how can i increase data frequency without modulation or share me solution for mod at transmitter(IR Light) and demod at receiver(Photodiode+TIA).

  • 0 in reply to Hardik Raval
    TI__Genius 15681 points

    Hello Hardik,

    You can use a simpler modulation scheme to achieve a lower data throughput if you do not want to implement a more complicated form of modulation.  Success has been had in the LiFi application using On-Off-Keying (OOK) alongside Manchester Encoding (Non-Return-to Zero, NRZ).

    I did write an orientation/brief on LiFi using high speed amplifiers: https://www.ti.com/lit/ab/slaaee8/slaaee8.pdf

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Intellectual 270 points

    Dear Alec,

    Well thanks for your suggestion.

    Is it possible for you to share related circuitary through which i can do OOK mod at transmitter and OOK demod at receiver.

    Demod is really needed at receiving end?

    Best Regards

    Hardik Raval

  • 0 in reply to Hardik Raval
    TI__Genius 15681 points

    Hello Hardik,

    I can share a circuit design we use for powerline communication with UART to OOK modulation.  It is a PLC booster pack design for wireline communication: PLC010935BP

    I do not have a design for laser diode/LED transmission and photodiode reception with OOK, though you would need a TIA stage and possibly an FDA stage to handle RX for OOK depending on your ADC choice.  Typically you can use an onboard DAC or interface IC for TX and use an amplifier & DC bias to send OOK through a laser diode/LED.

    You may either demodulate in software or use an interface device such as THVD8000, as in the wireline design.

    Best,

    Alec