Inverting input configuration of ADA4895-2

Hi, I am trying to implement High speed systems using the ADA4895-2 in inverting configuration. The circuit for the same is not that clear from the datasheet. And the circuit that I am using is not giving me the desired outputs for high frequency signals. Can you please guide me by providing an example of the high frequency signal with all the values of resistors and capacitances to be used ?

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    •  Analog Employees 
    on May 12, 2015 6:37 PM

    Hi Himanshu,

    Sorry for the very late response to this thread.

    The ADA4896-2 is decompensated for G>=10 stability. If you are using an inverting configuration, it is better to use a gain of -9 so that your noise gain will be equal to 10 to attain stability. You can refer to this tutorial about voltage feedback op amp: http://www.analog.com/media/en/training-seminars/tutorials/MT-033.pdf, figure 2 shows the different configuration of op amps and its corresponding equivalent signal and noise gain.

    However, if you will use a gain less that 10. Figure 50 of the datasheet, shows how to compensate and maintain the stability by adding RC circuit at the input. You may also refer to Table 11 for the component values to be used for gain <+10.

    Also, I would like to mention that the zero formed by RG and the input capacitance should be higher than the op amp bandwidth. To avoid stability issue, Figure 54 show how to compensate this by adding small feedback capacitor in parallel with the feedback resistor.

    Regards,

    Jay

  • 0
    •  Analog Employees 
    on Aug 2, 2018 2:51 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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    EZ Admin