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TINA/Spice/OPA1611: Phase Margin

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Replies: 3

Views: 132

Part Number: OPA1611

Tool/software: TINA-TI or Spice Models

Hi,

The result of an open loop analysis which is simulated with TINA-TI using the following schematic is shown, it seems that the phase margin isn't enough.
So, does the TINA-TI simulation model for OPA1611 support an open loop analysis ?
Please let me know if there is an error in the simulation method.

TIPD118 Verified Design Reference Guide
http://www.ti.com/lit/ug/slau518/slau518.pdf

Band pass filtered inverting attenuator circuit
http://www.ti.com/lit/an/sboa213a/sboa213a.pdf

OPA1611_Open_Loop_for_Attenuator.tsc

Best regards,
Kato

  • Hi Sadanori,

    I would do it this way:

    I would remove C4 and R7:

    sadanori.TSC

    See also this link:

    training.ti.com/ti-precision-labs-op-amps-stability-6

    Kai

  • Hi Kato,
    The model for the OPA1611 does model open loop gain and phase and output impedance of the OPA1611.

    In your design, the phase shift at Vout does not represent the phase margin of the circuit. You should instead measure the phase where feedback returns to the amplifier (the junction of R7, R5, L1, and C8), as Kai's post shows.

    Also, keep in mind that by breaking the feedback loop with L1, the input capacitance of the OPA1611 will no longer impact your circuit, so the input capacitors will need to be modeled externally as Kai has done with C3 and C5 in his schematic.

    More information on stability analysis, including techniques to address stability concerns, can be found in our TI Precision Labs series on Stability, the first video of which can be found here: training.ti.com/ti-precision-labs-op-amps-stability-1

    Regards,

    Alex Davis

    Precision Amplifier Applications - TI Tucson

  • In reply to Alexander Davis:

    Hi Kai-san and Alexander-san,

    Thank you for the explanation.

    As you pointed out, the open loop wasn't formed correctly and the probing point was also wrong, so I will review it and try to simulate it again.

    Best regards,
    Kato

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