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Behavioral model for a VGA

TUKA

Hello all,

I have modelled a Transimpedance amplifier (TIA) using verilogA as a second order low pass filter so that I could observe the effect of gain peaking (by tuning the Q factor). Now, in order to flatten the TIA response, I would like to cascade my TIA with a variable gain amplifier (VGA). 

My existing TIA has a bandwidth of around 50 GHz and a gain of around 60 dBohm.

I am interested in building a behavioral model for a VGA, just similar to a TIA using verilogA. My main focus is to flatten the TIA frequency response using the VGA response. 

Also, I would be interested to know how could I improve the bandwidth of the existing TIA using any suitable behavioral model.

Any leads towards this would be great!

Thanks!!

  • Dear TUKA,

    TUKA said:
    Now, in order to flatten the TIA response, I would like to cascade my TIA with a variable gain amplifier (VGA). 

    Please allow me to add a pedantic note to your request. A variable gain amplifier (VGA) is usually designed as a broadband amplifier without any intentional frequency compensation for prior stages or the response of a communications channel. If you are trying to equalize the response of the TIA, you might consider using some type of linear equalizer followed by a VGA.

    TUKA said:
    I am interested in building a behavioral model for a VGA, just similar to a TIA using verilogA. My main focus is to flatten the TIA frequency response using the VGA response. 

    It is not clear to me what parameters you are trying to include in your model. Hence, I can only provide a reference that includes an example listing for a low-noise amplifier with options for its IP3 and noise figure at URL:

    https://designers-guide.org/modeling/modeling-rf-systems.pdf

    If you have already created your TIA model, from my simplistic understanding, it seems as if you can use it as a template for a compensating linear equalizer with the inverse frequency response.

    Shawn

  • in reply to ShawnLogan
    ShawnLogan said:
    It is not clear to me what parameters you are trying to include in your model.

    Hi Shawn,

    Thank you for getting back to me, and thanks for providing me the right insights.

    I am trying to include the following parameters in my model:

    1. Gain range (for example -10 dB to +20 dB)   2. Bandwidth (around 50 to 60 GHz)   3. Noise figure    4. Linear-in-dB response

    Thank you!

  • in reply to TUKA

    Dear TUKA,

    TUKA said:

    I am trying to include the following parameters in my model:

    1. Gain range (for example -10 dB to +20 dB)   2. Bandwidth (around 50 to 60 GHz)   3. Noise figure    4. Linear-in-dB response

    This is helpful to me. I think the code shown in Listing 1 of the reference I included by Ms. Jesse Chan might serve as a very good starting point for your model. Its parameters, from the reference, are shown as Figure 1.

    Good luck TUKA!

    Shawn

    Figure 1

    from listing 1 of URL: designers-guide.org/.../modeling-rf-systems.pdf

  • in reply to ShawnLogan

    Dear Shawn,

    Thanks a lot for sharing the reference document.

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