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TINA/Spice/OPA843: OP843

Part Number: OPA843
Other Parts Discussed in Thread: TINA-TI, OPA857, OPA381, THS4504, OPA855, OPA847, LMH6629, LMH6554, LMH5401, ADC31JB68, ADS1243

Tool/software: TINA-TI or Spice Models

Hello;

I have a 1 photodiode and 1 Avalanche photodiode.

I have tried OPA857 before but I need to design new pcb for my application.

First I want to build TIA and second stage amplifier for 0-200Mhz signal

For the Photodiode(FGA01-Thorlabs)  I am unable to choose even though I almost memorize the Opamp specs.

First of all  I am in between OPA656-OPA843-OPA847- Opa381(I prefer msop package) and for second stage THS4504 Seems fine to me but I am not sure. After the second Stage I will use Microcontroller for Signal processing.

For the Avalanche Photodiode(G8931-10 Hamamatsu) 

I though I can use same opamps but Still I am not sure. The bandwith is the same as photodiode. I also used Opa857 before for this application.

But I am open to any suggestion  about my design.

The light I am trying to detect has really low illumination.

Thanks in advance.

Best regards

  • do you mean 200MHz not 200mHz?
  • I am sorry 200Mhz is the correct term
  • Thanks, so first of all that is a pretty wide bandwidth where the achievable transimpedance gain in the first stage will be set by the capacitance on the inverting node (APD + op amp parasitic) and the GBP. To get the best input referred noise, want as much there as you can so maybe the OPA855 might be the right part

    The G8931-10 shows 1pF max terminal C

    The OPA855 shows 8GHz GBP with 0.8pF input parasitic.

    so we have 1.8pF total, target 250Mhz Butterworth in the first stage (since the 2nd will roll this off). That says the noise gain zero can be 7.8MHz set by the 1/Rf*Cs meaning the maximum Rf = 11kohm.

    That then requires a feedback C across Rf 0.5pF (eq. 3 in this recent article where I finished up with a transimpedance design flow) which actually then gives a high F noise gain of 1+(1.8/0.5) = 4.6V/V - this might be a little low for the OPA855, might be still be ok but peaky.

    www.planetanalog.com/author.asp

    The other parts to look at are the LMH6629 and OPA847. Essentially using bipolar front end for the APD at least to get lower voltage noise.

    What is the total gain you are looking for (this would be in an impedance - first stage transimpedance, 2nd stage FDA). And, since the noise floor will be set by the first stage, the 2nd stage can be a CFA based FDA like the LMH6554 to get higher gain ranges there with >500Mhz BW.

    I discussed this 2stage transimpedance noise problem (at much lower frequencies) in this article,

    www.edn.com/.../Controlling-spot-and-integrated-noise-in-a-two-stage-transimpedance-design
  • Helle Mr. Micheal Steffes.
    First off all thank you for your detailed answer. And the articles cleared a lot of things for me.

    Actually, I can reduce the bandwidth 2Mhz -200Mhz even 2Mhz-150Mhz it could be the limit for my application but it can work.
    Opa847 has a fairly low input parasitic. I will try to solder myself, the package is important for me. Opa 855 is a really good choice and the peak is not a problem for me actually. But as You indicated it is a really high noise gain.

    I understand that there will be a noise problem with the second stage but it can be solved to some degree as stated in Your article.

    I am looking for a total gain of at least 10000 and even want to reach the maximum gain(1M could be perfect) but I am not sure if it is possible.

    Even my final stage Voltage value can be between 0-500mV and I can wrote some signal processing algorithm.
    Is it possible to reduce noise by limiting my outpu swing?

    Thanks in advance.

    Best regards.
  • Hello Ali,

    I found my transimpedance design tools - can run through some possible parts all targeting the same butterworth bandwidth in the first stage (200MHz) and see what happens in terms of noise. That will take a bit,
  • Hello Ali,

    So in summary, if you constrain your min Cf to 0.2pF the OPA847 and OPA855 give about the same noise but the OPA855 is being underworked with both designed for 5kohm. If you can deliver lower Cf, then the OPA855 becomes more attractive. The LMH6629 is less attractive due to its higher input C increasing the peaking part of the noise contributions.

    See attached.

    Some APD front end amps for an APD application.docx

    We have been presenting this transimpedance design flow for many years, shows where the equations come from  - and why the simplified noise expression might be enough. 

    Transimpedance design flow using high speed op amps.pptx

  • Hello Mr.Micheal Steffes;

    Thank you very much it could be really helpful.
    What do You think about the fga01? This is not an apd but the specs are really good. I even don't have to couple it to ADC. I can develop some analog signal processing part too.

    The signal is really important to me. And the signal is not constant sometimes it can just disappear but it is really fast.
    And my application is Biomedical engineering based. I will develop a system and Perfecting this part could be wonderful for me.
    I am reading Your posts again and the links are really useful and full of knowledge. Thanks again.

    I am waiting for your response.

    Thanks in advance.

    Best regards
  • Hello Mr. Micheal Steffes;

    I am amazed about your answers.
    Thank you very much. This way of analysing could solve my problem.
    I think I can find 0.2 pF Cf but it would be really hard for me to solder but I can make it work.

    I am reading the ppt and doc files over and over again.

    Do you have any suggestion about external Noise?

    Thank you again.

    Best regards.
  • So actually that 0.2pF is a typical 0603 thick film parasitic - no need to add a cap. I am off on the 2nd stage and finding it hard to get gains of even 20 at 400Mhz, so it may be that the FDA is the lower bandwidth stage and go back to the OPA855 with 5kohm and 0.1pF at 400MHz - there we would take two 2.5k 0603 and put them in series with their middle connection up off the board - then their two series 0.2pF will become 0.1pF.

    I am getting the LMH6554 at gain of 20V at about 200Mhz.
  • actually I am going to try the LMH5401 at gain of 20V, might make 200MHz.
  • Mr. Micheal Steffes;
    Yes, You are right I haven't thought about it. It can deliver my need with just a resistor.
    That is a really good idea to connect the resistor for a capacitive effect. But is there any special connection type to achieve that?

    LMH6554 and LMH5401 Looks really close to me. But maybe internal noise can be different I guess from the specs sheet.

    Thanks in advance

    Best regards.
  • Hello Mr. Micheal Steffes;

    I am trying to design as you suggested I will try Opa855 but I will also try to Opa847, For a second stage, I will try to integrate LMH6554.

    Do I need to integrate additional filtering because of my frequency bandwidth?

    Thanks for your all answers I am reading, again and again, all of them.

    Best regards.

  • Hello Ali,

    I got a little ways into TINA sims on this, and I don't think the full model of the OPA847 has quite enough for what you need. I was going to go on to the OPA855 for a bit this morning. Also, I have abandoned the LMH6554 in favor of the LMH5401. 

    This is going to be pretty noisy due to how wideband it is, some passive filtering will be required out of the last stage to control the integrated noise - is this DC coupled? If not, what min max band do you want? And is this heading to and ADC, need to set up Vcm on that as well and include input C in filter design - which ADC?

  • Hello Mr. Micheal Steffes;

    I will abandon the idea of using opa847. As you suggested OP855 seems best for me now. I can use 2Mhz-150Mhz bandwidth too if it can help about noise of the design.
    LMH5401 Noise performance seems very stable around my application BW.

    DC coupled could be more suitable for me. I was thinking about ADS1243 or ADC31JB68 as an ADC but I am not sure either. I can use Oscilloscope in the first place but eventually, I will need ADC and I am using Arm based microcontroller. I know ADC filter design could be quite troublesome. I am trying to find an answer all about these.
    And slowly solving the problem thanks to Your answers.

    Thanks in advance.

    Best regards.
  • Possible resistors for the transimpedance stage - have this working well for the OPA855, but it really does need 0.1pF feedback C.

    Years ago we used these (what was at the time being using in HP network analyzers). It would be nice if they had the very low parasitic C in surface mount - unless you have another idea, might want to check with them,

    prpinc.com/.../pr83518956-series-high-frequency
  • Ok Ali,

    I worked through quite a few issues to get to a final proposal - this should get you going for now - will undoubtedly need to be tweaked but I have to step off to other things for now. This is pretty fun stuff though for me. 

    The word file steps through the stages, with the final full circuit below that - can only attach one TINA file at a time.

    Some updated work on wideband APD amplifier April12.docx

    OPA855 plus LMH5401 plus filter.TSC

  • Hello Mr. Micheal Steffes;

    I have just looked at the design file and analysis You have sent me. I am really grateful for Your concern. 

    No words can express my gratitude to You. 

    Thank You over and over again.

    I have learned at least 3 month worth of research knowledge.  And the design is on another level for me and just examining them unbelievably fun for me cause it has a lot of good touch

    In our culture When a person teaches you to some stuff, It means the world to us. Thank you again. 

    I am a research assistant in Turkey. If you ever visit Turkey I would want to show my gratitude. Please contact me.

    Best regards.

  • No problem Ali, it was fun,

    There are many steps from what I have done to physical reality - you have a tough problem here. Best of luck and if you have questions in the future don't hesitate to ask. I would mark this one resolved and if you need to bring up something more open an OPA855 thread.
  • Hello Mr. Michale Steffes;

    Thank You again and again.

     I am trying to explore the design further. And I am also enjoying.

    It is a tough one but I believe I can do it with your help now.

    Thanks in advance.

    Best regards.