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ACF2101: Can't get the Spice model to run in LTSpice as expected

Prashanth Kumar
Prodigy 10 points
Part Number: ACF2101
Other Parts Discussed in Thread: TINA-TI, IVC102

Hello, 

I'm trying to evaluate ACF2101 against the conventional T transimpedance amplifier in terms of noise reduction.

As a first step I'm trying to simulate the ACF2101 in LTspice, however I'm issues with getting the output right.

  • The output more or less stays at 8.44V (instead of starting at 0V)
  • The integration of the output doesn't happen when Hold pin is ON
  • Though the input current is positive the output voltage isn't negative 

I have considered the timings for fs=10kHz

I have gone through the other posts but didn't seem to help.

Any support in identify the mistake or change required to get the simulation working would be helpful.

Thank

  • 0
    Guru 140200 points

    Hi Prashanth,

    does it work in TINA-TI?

    Kai

  • 0 in reply to kai klaas69
    TI__Guru* 93105 points

    Hello Prashanth,

    Please understand that LTSpice is the sole property of one of TI's competitors and we cannot provide assistance when users attempt to apply our models with their simulator. This comes about the property owner's use agreements that we must honor - just as they must honor our use agreements for our TI tools.

    Kai asked "does it work in TINA-TI?" TINA-TI is one of two PSpice based simulators that TI provides to users. The other is PSpice for TI. I tested the ACF2101 simulation model with TINA-TI and it readily converged and produced the results shown below. You could set this circuit up in the competitor's simulator and see if it provides the results you expect. I've provided the TINA -TI circuit file so that you can see how the piecewise linear sources are set up.

    I checked the ACF2101 model's PSpice syntax and they are the same for TINA-TI Spice and the model we provide for PSpice. Therefore, you should be able to run the model in other Pspice based simulators. Certainly file extensions and symbol files will be different and have to set up to be compatible with the particular simulator.

    The ACF2101 simulation model is about 30 years old and uses simplified models compared to what is used today. I believe that it does not accuratel simulate noise performance. There are no plans to update the ACF2101 simulation model.

    Regards, Thomas

    Precision Amplifiers Applications Engineering


    ACF2101_Test_01.TSC

  • 0 in reply to Thomas Kuehl
    Prodigy 10 points

    Hi Thomas,

    Thanks for the hint about TiNA and the simulation file. It helped.

    About the noise simulation you mentioned that ACF2101 is an older model and doesn't support it.

    How about ICV102U model, does it have noise parameters modelled ?

    Regards

  • 0 in reply to Prashanth Kumar
    TI__Guru* 93105 points

    Hello Prashanth,

    The IVC102 is actually handled by another TI division, but I looked over its Spice simulation model. It is quite dated (25 years) and I am not seeing anything in the model code that would indicate that there was an intention to model noise accurately.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Prashanth Kumar
    Guru 140200 points

    Hi Prashanth,

    apart from the Hold- and RESET-switches the internal amplifier of AFC2101 looks like a simple TIA, built with a JFET OPAmp. In "RESET"mode the TIA looks like this:

    The 10µVrms noise specification over a 250kHz band for the AFC2101 in the RESET mode can be translated to an estimated input voltage noise density of AFC2101 of

    10µVrms / SQRT(250kHz) = 20nV/SQRT(Hz)

    which absolutely makes sense for a good JFET-OPAmp.

    The noise of a TIA and the AFC2101 as well is highly dependent on the actual values of the detector capacitance and the integration capacitance as being discussed in this appnote:

    https://www.ti.com/lit/pdf/sboa032

    So it's very simple to estimate the final noise of your application, even without performing a noise simulation with TINA-TI Relaxed

    Kai