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Original question:

INA1620EVM: Board mods required for 18dB of gain, with +-15v supply powering the board.

INA1620EVM: Resistors required for 13db of gain

Mike Davis
Prodigy 230 points
Part Number: INA1620EVM

Hello,

I'm a bit confused. I replaced R1 & R7 with 1kohm resistors, and R2 & R6 with 10kohm resistors. I'm feeding the right channel audio input 1v. However I'm only getting 1.75v on the output, or 4.86db of gain. I thought with a 10 to 1 ratio I should be getting 10v output, but it appears I misunderstood something. Is this the result I should be expecting? 

If I wanted to achieve 13db of gain, or 4.5v on the output with 1v input, which resistors should I use in R2 & R6, if I'm using a 1kohm resistor in R1 & R7?

Thanks,

Mike

  • 0
    TI__Genius 10850 points

    Hi Mike,

    You're right, if you set R1&R7 = 1k and R2&R6 = 10k, you should get a gain of 10V/V = 20dB. I wonder if there's something else in your circuit configuration that might be contributing to this odd behavior. Can you share a quick schematic of this with power supply and input/output connections?

    -Tamara

  • 0 in reply to Tamara M Alani
    Prodigy 230 points

    Hi Tamara,

    I don't have a Schematic. I'm feeding the DC inputs a solid +-15v DC. And everything is connected properly. I connect the inputs to my audio analyzer signal generator, and the outputs to  my audio analyzer inputs. And when I feed it 1v, I get 1.75v output. I ramp it up to 2v and I get 3.5v output. It measures perfectly with a THD+N of -108dB with input impedance of the analyzer set to 100K. 

    Thanks,

    Mike

  • 0 in reply to Mike Davis
    Prodigy 230 points

    Hi Tamara,

    I discovered the problem. The 0 ohm resistors need removed otherwise they put the internal 1K resistors in parallel with the external resistors. The end result was 0.83K for the feedback resistor's and 0.47K for the input resistors. The math explains the end result. 

    Thanks,

    Mike