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OPA818: AOL and GBWP variance

Bruno Dion1
Prodigy 40 points

Part Number: OPA818
Other Parts Discussed in Thread: OPA858,

I am working on a near 50MHz design using a XX kohms feedback resistor for a high volume application that will last several years.
AOL is stated as 92dB typ with 85dB min. Is AOL variation is primarly DC gain or GBWP is also affected?
Say gain at 50MHz is 35dB, what will be the variation on this 35dB which may affect directly the receiver BW at high volume?
Currently I have a 16% exceess BW, will that garantee my minimum BW at high volume for the next few years to come?
BW is related to SQRT(A(50MHz), so BW variation is 1/2 of the gain variation. (from CS0288362 rerouted to E2E)

  • 0
    Guru 48395 points

    Well Bruno, this came up recently for another device in this family - the GBP is usually far less variable than the DC Aol. I believe that discussion ended with a +/-15% GBP range of device and temp. If you are doing a transimpedance design, that gets into the Fo  and Q as a +/-sqrt (1.15) = +/- 1.07% closed loop variation - make sure you consider the source C variation as well. 

    e2e.ti.com/.../3478262

  • 0
    Prodigy 40 points

    Hi Michael

    Thanks for your answer, this sounds encouraging that GBWP VAR << AOL VAR.  

    I need to demonstrate production readiness for high volume and for the years to come. 

    By precaution, I did increase my margin, better more than less. 

    I looked at the OPA858 post where you cited the 15% GBWP variation.  May I ask where you found this 15% data; i.e. a TI source?

    Best regards,

          Bruno Dion

  • 0 in reply to Bruno Dion1
    Guru 48395 points

    That came from the IC designer, 

    If you are really trying to future proof you design, perhaps you should run a monte carlo on the external element variations - I, or the TI folks, should be able to provide a min/max GBP model for the OPA818. Schematic would be required to go any further. 

    I was doing some GBP min/max sims for this article on setting the min GBP required for a MFB filter design, In the old days, that cap was a line called the "dompole" for dominant Aol pole, 

  • 0 in reply to Michael Steffes
    Prodigy 40 points

    Hi Michael

    Thank you very much for the article, this takes care of my question for good. 

    I will probably have less than 7% variation on this TIA receiver when considering the Cf effect.

    Best regards,

    Bruno