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I'm still struggling to apply my limited knowledge of op amps... so I've created a problem to solve... but need your help.

BigG

I can follow along other peoples projects but it quickly becomes apparent that I do not fully grasp the fundamentals when I try and solve a problem of my own.

So here is my own problem I'm trying to solve, as shown below:

image

I have two scenarios. I think the first one is fairly easy, but it is knowing how to achieve the 2nd that is more challenging, especially if you wish to say use the same op amp and even the same circuit the 1st.

How does one go about this?

As per usual, I very quickly try and over-complicate matters... like when spotting these types... Transresistance amplifiers... and wondering whether I should/could use these...

Anyway, no doubt this is a very straightforward problem for the experts.

I look forwards to getting some tips.

Thanks.

C://

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  • 0 in reply to beacon_dave

    Using that document as my guide here are my design equations.

    Case 1:

    image

    And same answer for Case 2... positive m & negative b.

    This moves us onto section 4 of design guide...

    This section then asks "Choose Rf (may be suggested on data sheet)"... ok then...

    Onto Farnell's website and... Operational Amplifiers - Op Amps: 7,260 Products Found!

    This may take a while...thankfully choosing "those in stock" narrows it down a bit (LOL). Now down to 1,691 Products Found!

    As I'm using a TI guide, how about a TI Op Amp... now down to 620... getting better.

    Assuming that I only need 1 amplifier... 250 Products Found.

    Now not sure... looking at the cheapest doesn't help matters as search criteria on website gives options like "supply voltage range".

    As I'm using a 3V3 MCU, I assume that's the value to use... Now down to 116 Products Found.

    So picking the first 3 on the list gives me... LMV821M5/NOPB, TLV8801DBVT, and LM741CN/NOPB

    The LMV821 and LM741 show Rf as R2, and show a typical value of 4.7k... so using that.

    image

    Now I have two values for R1.

    The document then talks about tuning.

    Two options are given. One suggests tweaking R1 to compensate for errors and the 2nd option is to use a 2nd op amp.

    So now what... am I on the right track...

    ... ah I see Figure 7 has been suggested as another response... with some values... and using LM307

    Still, I would like to understand how one gets to that answer.

  • 0 in reply to BigG

    It is interesting to notice, while searching for the right product, that there are quite a lot my 2 channel op amps available... is this to allow you to design a more accurate solution using one component as noted in the guide.

  • 0 in reply to BigG

    A few reasons: there is the immediate real estate advantage because dual and quad opamps take less space than 2 or 4 discrete ICs + their individual decoupling caps.
    It can also play in your advantage that they are often better matched than two single opamps of the same type.
    Disadvantage is often increased cross-talk.

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