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TIDA-01351: TIDA-01351 : Question about gain stage

kang seungpum
Prodigy 80 points
Part Number: TIDA-01351 

Hello.
This is a question regarding the gain stage mentioned on page 9 of the TIDA-01351 document.
The formula of gain is 10*[R2/Rth+R1]

Is [R2/Rth+R1] correct?

Thanks
  • 0
    TI__Guru* 93105 points

    Hello Kang,

    The text states in 2.3.1.1, Summing Circuit and Gain Stage section, "... the Thevenin equivalent of all summing resistor R (1 kΩ; see Figure 3) is Rth 120 Ω (see Figure 4). This Rth (120 Ω), R1 (887 Ω), and R2 (10 kΩ) forms a gain of 10 [R2 / (Rth + R1)]."

    It looks like a comma was left out of the text after "forms a gain of 10" resulting in a gain equation that incorrectly places a 10x multiplier in front of the resistor relationship. In actuality, when you apply the Rth, R1 and R2 values and leave the "10" out before the resistor equation you obtain a gain of about 10 V/V which is correct:

    G (V/V) = [R2 / (Rth + R1)] = [10 kΩ / (120 Ω + 887 Ω)] = 9.93 V/V or about 10 V/V.

    The gain equation that you stated is correct.

    Regards, Thomas

    Precision Amplifiers Applications Engineering