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Original question:

VCA810: Non-linear issue of VCA810

VCA820: Non-linear issue of VCA820

Lin_Charles
Expert 4260 points
Part Number: VCA820

Hi team,

   I want to use this device as below,  Rf=845Ohm, Rg=16.9, Vg=2V, which means Avmax=40dB;

   When I apply VG1 signal, Vpp=5mV, f=20MHz, we can see that Vpp of VF1 is about 700mV. This is not aligned with the gain*Vpp=500mV. What is the reason? 

   Also, I am not clear about the relationship between Vg and gain, it is not clear in our datasheet. Please help answer these two questions ASAP. I have attached the TINA file to help you simulate this device. Thanks. 

slac091b.tsc

  • TI__Expert 7960 points

    Hi Charles, 

    Unfortunately it appears that the model is not simulating correctly at the high gain settings. We will work to get the model updated, but it may take some time because this is in an older format. For now I suggest that the customer uses the datasheet information. We can also send them an EVM board to make lab measurements. 

    The Vg voltage controls the gain from zero V/V up to 2 times Rf/Rg. This allows you to set the maximum gain with Rf/Rg and then control the gain in real time with a voltage signal on Vg. 

    Regards, 

  • in reply to Jacob Freet
    TI__Expert 4260 points

     Hi Jacob,

        Thank you for your help here. Please help modify the simulation model ASAP. BTW, I want to confirm that if this device can be used as below requirement,

    Vs=+/-5V, Vppmax=2V, frequency=30MHz, AVmax=40dB?? We still cannot find one proper solution to realize it.

         One more question here, if the max gain is 40dB, which means, when Vg=0, gain=0dB, Vg=2V, gain=40dB? Right? Thanks.

  • in reply to Lin_Charles
    TI__Expert 7960 points

    Hi Charles, 

    When you say Vppmax = 2V, is that at the input or the output of the device? 

    At Vg = 0 the gain will be 0 V/V. You can see the plot in figure 64 of that datasheet that shows the gain curve for a 40dB gain setup. 

    Regards, 

  • in reply to Jacob Freet
    TI__Expert 4260 points

    Vpp=2V in the input of the device.

  • in reply to Lin_Charles
    TI__Expert 7960 points

    Hi, 

    Since this discussion has been taken to email, I will close the thread. 

    Regards,