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OPA1632 simulation bug

guilherme.muller
Intellectual 270 points

Other Parts Discussed in Thread: TINA-TI, OPA1632, THS4551, THS4120

It seems that there is a simulation bug in TINA-TI that is messing with the results.

I was simulating a MFB Filter using OPA1632 and noticed that sometimes the signal phase shifted. I've noticed also that the bug is totally repeatable. I am using version 9.3.150.4 SF-TI. Attached is the circuit I am using.

If I delete U1 and add another OPA1632, the phase get shifted (180 degrees). If I do a Ctrl+X on U1 and paste it in another place, than move to the correct place, the phase shift back to normal.

The correct behavior should be the second one, when both signals are in phase (confirmed using TI Filter Pro and another Spice program).

Is this correct or am I doing something wrong?

Regards,

Guilherme

FILTRO_Novo.zip

  • 0
    TI__Mastermind 41310 points

    Guilherme,

    When I open your .TSC file, I get the following errors when I run an ERC:

    So, when you are cut and pasting the device, the wires from the output are NOT connecting again and you are seeing the input signal without being processed through the amplifier. If you connect the wires up, you get the original simulation. If you run the original simulation with the output disconnected, you will get the two signals overlaid as you showed in your post.

    We will have to look into why the phase shift occurs in the simulation. I don't have an answer for that currently.

  • 0 in reply to Britt Brooks - Online Design Tools
    TI__Genius 12631 points

    Hello Guilherme,

      I confirmed Britt's findings with regards to the unconnected output. Also, a Fully Differential Amplifier (FDA) is inherently inverting. Please see this document for a more in-depth explanation of FDAs.

    I also noticed that you are using the OPA1632 in +/-2.5V supplies. TI released a new high-precision, high-speed FDA, the THS4551 earlier today. Its noise is a little higher than the OPA1632 but it has similar bandwidth at a fraction of the quiescent current. The datasheet for the product is shown below. Please contact me in case you would like further help in designing with your FDA and choosing between the OPA1632, THS4551 or other FDA.

    -Samir

  • 0 in reply to Samir Cherian
    Intellectual 270 points
    Dear Samir,

    Thank you very much for the information. I'll read the documents carefully, because I have, indeed, doubts with FDAs. Can I email you with the details?

    About TINA-TI, my mistake. I thought that the wires would connect themselves as soon as I moved the component. Didn't realize that the wires were bigger (I was testing with THS4120 which have slightly smaller output pins).
  • 0 in reply to guilherme.muller
    TI__Genius 12631 points

    Hello Guilherme,

      Sure you can always contact our applications support team on the high speed E2E forum below. Contacting us on E2E will ensure that someone on the team will see it and respond in a timely manner if I am travelling.

    https://e2e.ti.com/support/amplifiers/high_speed_amplifiers/

    -Samir