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TINA/Spice/TINA-TI: Model accuracy

Arie Menscher
Prodigy 200 points
Part Number: TINA-TI
Other Parts Discussed in Thread: THS4140

Tool/software: TINA-TI or Spice Models

Hi,

I have used TINA-TI simulating basic behavior of THS4140 and getting results which are different than expected.

I would like to know about accuracy of the modelling, as shown by simulation results.

Example 1- Gain is supposed to be 10, according to device recommendation, yet I get different value (9.97). Simulation conditions are ideal, so only device parameters should affect results.

Example 2 - checking for device parameter of Vos (input offset voltage), specified by datasheet between 1 and 7mV, yet in simulation I see absolute zero

These are a few examples, and not clear to me whether the specific device model accurately reflects device parameters?!

How can I confirm?

Thanks,

Arie

  • 0
    TI__Intellectual 820 points
    Hi Arie,

    Please share your TINA schematic files hereby.

    Regards,
    Ahana
  • 0 in reply to Ahana Ghosh
    Prodigy 200 points

    THS4140 Test Circuit.TSCHi,

    Please see attached (relates to example 1).

    Thanks,

    Arie

  • 0 in reply to Arie Menscher
    TI__Genius 9775 points
    Hi Arie,

    For the gain, I think this is accurate because the open loop gain is around 68dB and if you work out the math, the closed loop gain of amplifier due to finite open loop gain will not be able to achieve perfect 10.0. Rather approximately it will be around 10 / ( 1 + (1+10)/2500) = 9.96.

    For the offset, most likely there was a datasheet revision by comparing the date on the model vs. the datasheet; however, you can adjust the offset by yourself by putting a small voltage source externally in series with the Vinp pin (or internally inside the model if you want, but it's easier to put it externally). You can adjust the offset with respect to the nominal value of the datasheet which is 1mV or if your application is sensitive to offset, you can definitely adjust it to the maximum value of the datasheet which is 7mV .

    Hope this helps,
    Herman
  • 0 in reply to Herman Theodorus
    Prodigy 200 points

    Hi Herman,

    Thanks for the feedback, it helps a lot.

    You have addressed the 2 parameter examples as stated in my post, regarding gain (which is critical parameter for the device) and offset, and for the more 

    general perspective question I had ( ...not clear to me whether the specific device model accurately reflects device parameters..) it seems to me from your reply that

    the answer would be YES ..

    Another example leading to my dilemma is the fact that I see in the simulation a difference between the positive and negative outputs of the device: for a 1V differential 

    input signal, I get output 5.02 V and -4.95 V values respectively, which summed together is 9.97V and 9.97 gain - not clear if it reflects device behavior or is the result of something else?!

    Another way of addressing the question is maybe the way model has been validated vs. the datasheet parameters?!

    Thanks,

    Arie

  • 0 in reply to Arie Menscher
    TI__Genius 9775 points
    Hi Arie,

    I was looking about 5.02V and -4.95V at the output that you mentioned. I checked the datasheet and unfortunately, the datasheet does not mention about VOCM common mode offset. But if you work out the math (-4.95 + 5.02)/2 = VOCM voltage and with VOCM pin is at 0V, this translates to about 35mV common mode offset.

    It is very possible that as we perturb the output voltage and send the signal through the VOCM and Main signal path system of the FDA amplifier, it will generate more VOCM/Commond Mode offset.

    As I said, it is difficult to tell from the Datasheet because the datasheet does not have that information.

    The best way if you want to know for sure, probably to post a question to the product specific group within E2E which is "Amplifier Forum" and assign it to HSAMP group if you have that option. Alternatively, you can also order and EVM Sample of the part and check around it.

    Herman
  • 0 in reply to Herman Theodorus
    Prodigy 200 points

    Hi Herman,

    Thank you for your reply, it puzzled me also. I will check it further.

    Arie