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1Ghz opto sensor

BRUNET Richard
Prodigy 40 points

Other Parts Discussed in Thread: LMH6629, LMH6401, LMH5401, THS4304, LMH6882

Hello,

I am new (from Paris) on your forum.

I need to build a sensor for laser pulse 1ns every second with 10.000 dynamic.

Is it possible to find a logAmp for that or a linear amplifier with a variable gain ?

Regards,

Richard

  • 0
    TI__Genius 13935 points
    Hi Richard,

    Do you need single ended or differential amplifiers? Is your photo detector embedded with the laser? We will need more details for a full recommendation.

    Single ended:

    We have some variable gain linear amplifiers. The VCA82x series may be useful. You may want to use one of our TIA amplifies for the photo diode interface. We have the OPA85x series of TIA amplifiers. The LMH6629 is also well suited for use as a TIA.

    Differential:
    I have successfully achieved over 1GHz of bandwidth by using the LMH5401 as a TIA with a high speed photo diode. The LMH5401 could be followed by the variable gain LMH6401.


    Regards,
    Loren
  • 0 in reply to Loren Siebert 1
    Prodigy 40 points
    Hi Loren,
    The laser and the sensor are not together.
    My sensor is single shot every each second only.
    I hope to use a Pin diode to get the photons pulse - A DC pulse. A single ended amplifier would be sufficient.
    I need variable gain to adapt the pic value in a linear way to send it to a comparator.

    Regards,
    Richard
  • 0 in reply to BRUNET Richard
    TI__Genius 12631 points

    Hello Richard,

     Is 1ns the total pulse width or is it the rise/fall time of the input pulse? If 1ns is the total pulse width then assuming a rise/fall time of say 200ps, the amplifier will require a closed loop bandwidth of 1.75GHz. This is getting quite high. We don't have any log amps that approach this speed. We do have linear amplifiers that have the desired bandwidth but in order to recommend the appropriate amplifier more information is needed.

    Can you please let me know:

    1. What is the input capacitance of the photodiode you plan to use? (If you have a datasheet could you please send that as well).

    2. What kind of transimpedance gain are you hoping to achieve. If you don't know the transimpedance gain can you please let me know what the range of expected output current from the photodiode is?

    We can follow up the transimpedance gain stage with a variable gain stage. Do you plan on feeding the output of this signal chain to a high-speed ADC? If so what model of ADC are you planning on using?

    Finally can you please let me know the end application?

    Thanks,

    -Samir

  • 0 in reply to Samir Cherian
    Prodigy 40 points

    Hello Samir

     Is 1ns the total pulse width or is it the rise/fall time of the input pulse?

    - It's around 1 ns, we can loose a part of the dynamic.

    We do have linear amplifiers that have the desired bandwidth but in order to recommend the appropriate amplifier more information is needed.

    Can you please let me know:

    1. What is the input capacitance of the photodiode you plan to use? (If you have a datasheet could you please send that as well).

    - It could be 2 pf with some reverse bias. We can change the model at this time.

    2. What kind of transimpedance gain are you hoping to achieve. If you don't know the transimpedance gain can you please let me know what the range of expected output current from the photodiode is?

    - A very low one, we have too much photons. I hope some volts, with some mW. the worst case is 40µW with a 0.3A/W.

    We can follow up the transimpedance gain stage with a variable gain stage.

    - Yes, that is interesting we have from 40 µW to 1000x40µW.

    Do you plan on feeding the output of this signal chain to a high-speed ADC?

    - No. that is just a test for an UAV to stay some meters up to the sea.

    Finally can you please let me know the end application?

    - A toy TOF rangefinder for an UAV to stay some meters up to the water with a good precision.

  • 0 in reply to BRUNET Richard
    TI__Genius 12631 points
    Richard,

    For the 1st stage the THS4304 is one option. The feedback resistance should be in the 1kOhm range. I am still confused as to how you plan to observe these signals?

    I suggest following the transimpedance stage with an LMH6882 amplifier; note that this is a differential output amplifier.