whether negative supply on pin -Vs required for ADA4895-1?

Does the negative supply to -Vs for amplifier plays any vital role ? I have grounded -Vs pin and  following issue was faced,

Closed loop gain was reduced and virtual grounding not happened properly, so my output voltage was reduced.

But when i have given -5V to -Vs pin, then im getting good Closed loop gain and virtual grounding comparing to GND on -Vs pin.

  • 0
    •  Analog Employees 
    on Oct 16, 2020 5:02 AM 1 month ago

    Hi,

    The -Vs also dictates your Input Voltage Range or VCM.
    For an instance in your case, if you have used +/-5V for your supply, then your input voltage range would be -4.9 to 4.1V.
    Where as, if your supply is 5V/GND, then your VCM is 0.1 to 4.1V.
    Having said that, using different supplies means different VCM.

    Please make sure your input is within the input range or you can use a Vcm to shift your input just to make sure that it is within the input voltage range.

    Hope this helps.

    Thanks and regards.

  • 0
    •  Analog Employees 
    on Oct 19, 2020 4:28 AM 1 month ago

    Hi,

    Below is example of simulation using single supply vs. dual supply (Vout 1 vs. Vout2).

    As you can see, the closed-loop gain is affected.

    But, ensuring that the input is within the VCM of single supply, the closed-loop gain is now the same to the dual supply (Vout1 = Vout3).

    Hope this helps.

    Thanks.

  • Thanks for the reply. I undershoot that total supply voltage (+Vs)-(-Vs) will decide the closed loop gain , not the dual supply voltage.

    This circuit is transimpedance amplifier ADA4895-2 with photodiode as input.

    First image - Gnd is connected to -Vs pin. Virtual grounding is not happening

    Second image - -5V connected to -Vs pin. Virtual grounding is happening perfectly.

    As you said closed loop gain may change due to total supply voltage, but why virtual grounding is affecting in first image?