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ONET2591TA: TIA with logic like output

Part Number: ONET2591TA
Other Parts Discussed in Thread: OPA857-DIE, , OPA857, OPA656-DIE

I am building a simple optical receiver for 10Mbps RZ in a TO-18/TO-46 package. This receiver needs to output el. signal which will be > 0.7 x Vcc for "on" signal and < 0.3 x Vcc for an "off" signal. 

I have some experience with PIN - TIA assemblies but these will not give me desired voltage output. 

Do you have something appropriate for the job?

Our optical signal will be at 850nm, we are using GaAs PIN PD, signal data rate is 10Mbps modulation RZ. I know that 2.5G TIA is an overkill, but perhaps you can suggest something more appropriate. I am ideally looking for low bandwidth amplification to achieve sensitivity < -30dBm.

  • Hi Peter, 

    We don't have any of our dedicated optical networking chips in the speed range you are looking for. However, you may be able to use one of our standard analog transimpedance amplifiers in this application. A couple of further questions. 

    1. Do you need the amplifier available as a bare die or would a packaged device work? 

    2. What is your expected input current range from the photodiode? 

    3. What is your VCC? 

    Regards, 

    Jacob 

  • Dear Jacob,

    Thanks for your reply. Can you send me a link to your dedicated optical networking chips?

    1) Bare die is preferential since this can be placed inside TO-can.

    2) The photodiode will generate maximum 0.5 mA.

    3) ideally around 5V, but I could accept 3.3V.

    Thanks,

    Peter

  • Hi Peter, 

    Here is a link to our optical networking IC's page. https://www.ti.com/interface/optical-networking-ics/products.html

    We do have devices like the OPA857-DIE that might work for you and are much simpler than our ONET devices, but the issue is that the output swing is limited and does not reach your target values based on VCC. The optical networking TIA's should still work for you, they are just quite a bit faster than you require. 

    Best, 

    Jacob 

  • Dear Jacob,

    I think the closest match to what is needed is ONET2591TA. Having said that this is very fast for our requirements and what I need is ideally slower than 200MHz. The other issue with ONET2591TA is that it has differential output, while I need single ended output. 

    I think that OPA857 is not suitable. 

    Are there any other options that you can propose?

    Thanks,

    Peter

  • Hello Peter,

      The ONET2591TA would likely not be suitable for your design requirements due to its speed.

       Jacob's suggestion of the OPA857 would still work as single-ended output. The device is pseudo-differential, where the signal is seen at OUT pin of the device. OUTN is an optional reference which is beneficial when interfacing with ADCs. 

      What is the expected input capacitance to the amplifier? I would suggest also looking into the OPA656-DIE even though it does require a high voltage supply. 

    Thank you,

    Sima