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OPA657 spice macro model behavior

Gaston Arrigo
Prodigy 20 points
Other Parts Discussed in Thread: OPA657, TINA-TI

Hello,

 

I need some help with the behavior of the spice model for OPA657 opamp. I'm simulating a transimpedance amplifier with the OPA657 but I found a diference in the behavior depending on which revision I use.

I tested with the following two macro models (I transcribe only Headers of .sub files):

Model (1)

* OPA657  Non-Unity Gain Stable, FET Voltage Limiting Amplifier
* REV. A - Created 1/21/02 Rea Schmid
* REV. B - Created 2/26/02 Rea Schmid - Purpose to adjust voltage and noise curves

Model (2)

* OPA657  Non-Unity Gain Stable, FET Voltage Limiting Amplifier
* REV. A - Created 1/21/02 Rea Schmid
* REV. B - Created 2/26/02 Rea Schmid - Purpose to adjust voltage and noise curves
* REV. C - Created 6/27/06 Xavier Ramus - to correct input stage oscillation
* REV. D - Created 10/23/06 Xavier Ramus - To correct Noise
* REV. E - Created 11/22/06 Xavier Ramus - To correct behavior in transimpedance applications

The model (1) Is included in TINA software and model (2) was downloaded from TI webpage. I'm sure I should use model (2) because the REV.E. But as I had some doubts about the behavior, I tested the circuit of page 7 of the datasheet (Frequency response vs capacitive load).

I obtained a very acceptable simulation result with model (1), but an unclear result with model (2). I use the same circuit, even the same file. I only change the component macro model.

Simulation obtained with model (1)

Simulation obtained with model (2)

I would really appreciate if you can help me and tell me about what is going on and explain me about these behavior differences. I'm designing a transimpedance amplifier with BW=20MHz and I'm trying to have an improved simulation to compare the PCB behavior vs the simulation.

Thanks a lot in advance

Gaston

  • 0
    TI__Expert 4950 points

    Hi gaston,

    In TINA, the header is

    .SUBCKT OPA657 + - V+  V- Out

    whereas in Pspice the header reads as

    .SUBCKT OPA657 + - Out V+ V-

    Changing the arrangement of the node in the header will make the Pspice model work in TINA.

    Note that for transimpedance amplifier, the Pspice model should yield better result than the earlier rev TINA model.

  • 0 in reply to Xavier Ramus
    Prodigy 20 points

    Xavier Ramus said:

    Hi gaston,

    In TINA, the header is

    .SUBCKT OPA657 + - V+  V- Out

    whereas in Pspice the header reads as

    .SUBCKT OPA657 + - Out V+ V-

    Changing the arrangement of the node in the header will make the Pspice model work in TINA.

    Note that for transimpedance amplifier, the Pspice model should yield better result than the earlier rev TINA model.

    Dear Xavier,

    It worked correctly! Thanks a lot for your help!

    Best regards!

    Gastón

     

  • 0 in reply to Xavier Ramus
    Prodigy 10 points

    I have tried to import the model into Microwave Office and I get a syntax error on the header. It seems to have problems with the addition symbol being used as a node name.

    I am not terribly familiar with Pspice and I would like to ask if all the addition symbols (+) refer to the node name and hence may be replaced with something less ambigous or whether such a symbol is also part of the syntax and hence it ought to be replaced selectively.

    Best Regards

    Francesco

  • 0 in reply to Francesco Fornetti
    TI__Genius 13935 points

    Hello Francesco,

    It is unusual for a single symbol to be a node name.  I don't see why you could not use new names, however, it is not only just the header, the node names are used in the net list and will need to be changed through out the whole file. This can be rather tedious.  

    I am not familiar with Microwave Office.  Is it possible to use the TINA-TI simulator instead?

    Regards,

    Loren