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ADA4950 BW and Vocm Questions for Design

Can you provide advice for proper design considerations for the following questions:

1) The signal we're passing is only operating between 20Hz and 15Mhz.  Would reducing the Bandwidth of the device help prevent oscillations, and if so what would you recommend as the best method of rolling off excess Bandwidth?

2) We are passing a signal that we'll always be centered around 0V (no DC offset).  

   a) Do you recommended tying Vocm to 0V to be certain we meet this condition independent of the power supply rails?  

   b) Is tying directly to 0V sufficient or do we need to have some other impedance?

We are operating with a gain of 1.

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  • Hi Adam,

    1. You can reduce reduce the bandwidth in two ways. First is putting a capacitor in the feedback loop and the other one is an external LPF. A single-pole, RC filter, might be enough for you but you have to include the load into calculations. However, I would suggest an external 3-pole Butterworth LPF since it has a maximally flatband response. See figures below.

     

    I have designed this at 45MHz cutoff to make sure that the 15 MHz signal is still at flatband, within 0.1 dB flatness. You can either implement this or create your own filter for your design optimization.

    2. It's okay to directly tie the VOCM pin to ground to ensure 0V common mode.

    Regards,

    Jino

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  • Hi Adam,

    1. You can reduce reduce the bandwidth in two ways. First is putting a capacitor in the feedback loop and the other one is an external LPF. A single-pole, RC filter, might be enough for you but you have to include the load into calculations. However, I would suggest an external 3-pole Butterworth LPF since it has a maximally flatband response. See figures below.

     

    I have designed this at 45MHz cutoff to make sure that the 15 MHz signal is still at flatband, within 0.1 dB flatness. You can either implement this or create your own filter for your design optimization.

    2. It's okay to directly tie the VOCM pin to ground to ensure 0V common mode.

    Regards,

    Jino

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