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THS3120 gain

Haider Al kanan
Prodigy 90 points
Other Parts Discussed in Thread: THS3120I have THS3120 EVM. I measured the voltage gain in the lab and it was 2 , however I need the gain to be 10, Which resistor should I change to get the gain of 10? The R4 on the board is 499, and R3 looks like 124ohm , so why is the gain is 2?
  • 0
    TI__Genius 14825 points
    Thank you for your question! I have moved your post over to the forum where the best equipped TIers to help you are located.

    Have a great day,
    Jason Bridgmon
  • 0
    TI__Genius 13935 points
    Hello Haider,

    Are you measuring inverting gain or non inverting gain?
    Inverting gain is R4/R3. Non inverting gain is 1+R4/R3.
    In either case the observed gain will be reduced by any resistors installed at the amplifier output (R7A,R7B,R8A,R8B).
    When using 50 Ohm test equipment it is common to use a 50 Ohm matching resistor on the EVM. This will cut the observed gain by 6dB (factor of 2).
    Do you need the 50 Ohm matching resistor? If not you can use an R4 value of 1.24k Ohms for a gain of 10. If you do need 50 Ohm matching, then you need a total gain of 20 which would require a 2.48kOhm feedback resistor.

    Regards,
    Loren
  • 0 in reply to Loren Siebert 1
    Prodigy 90 points
    Loren, Refer to page 15. In data sheet. www.ti.com/.../slos420e.pdf That table in page 15 doesn't consider the 6dB drop due to matching which confused me. I am trying to use noninverting conf. With 50ohms source and load impedance. Thanks for answer.