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OPA4727: OPA4727 Inverting Summing Amplifier

Hank Wang
Prodigy 50 points
Part Number: OPA4727

Hi

I designed a inverting summing amplifier by OPA4727.

Here is my schematic.

+V= 3.3V, -V = -2V. V1~V16 = 1.12V.

Do input voltage(V1-V16) exceed the range of OPA4727?

Thanks

BR,

Hank

  • 0
    TI__Guru 55466 points

    Hi Hank,

    The OPA4727 summing amplifier has a gain an output transfer function of:

    Vo = -  (RF / R1 * V1+ RF / R2  * V2 .. + RF / R16 * V16)

    The gain for each input is RF / Rx = 16k / 1k =  16V/V.  If I understood correctly, each input V1-V16 is +1.12V.  The total ideal output will be at 16*16*1.12V = - 286-V/V.

    The op-amp is powered by VS(-) =-2V and VS(+) =+3V, hence the amplifier output will be out of range, in the negative rail.

    Perhaps you meant, RF = 1kΩ  and R1..R16 = 16kΩ ?

    Kindly let me know if I misinterpreted the input voltages, or misunderstood the circuit.

    Thank you and Kind Regards,

    Luis

  • 0 in reply to Luis Chioye
    Prodigy 50 points

    Hi Luis

    Thanks for your reply.

    It's my mistake. Yes, my design is that Rf = 1k , Rx = 16k. The gain of input is RF / Rx = 1k / 16k =  1/16 V/V.

    The total ideal output will be at 16*(1/16)*1.12 = - 1.12V.  +V= 3.3V, -V = -2V.

    Will the amplifier output be under range? Correct?

    Becasue I am not sure that the gain will be effected before or after the amplifier input.

    If the gain effected before amplifier, the input volatge value will be out of range.

    Updated schematic.

    Thanks

    BR,

    Hank

  • +1 in reply to Hank Wang
    TI__Guru 55466 points

    HI Hank,

    Yes, as shown above, the summing amplifier with RF = 1k,  and R1..R16 = 16k, and assuming R20 and R21 on the negative supply connection are unpopulated, the circuit will work with input signals at V1..V16 = +1.12V.  The output will be around ~-1.12V.  You could add a small feedback capacitor for stability. 

    Thank you and Regards,

    Luis