A summing amplifier has the following values: Rf = 10 kΩ, and R1=R2=R3=R4=40 kΩ. Which of the following statements is true about the circuits?
A) The circuit will not work with the values given.
B) The output will equal the average of the four input voltages.
C) The output will equal the sum of the four input voltages.
D) The output will equal the sum of the squares of the four input voltages.

Question

Quizplus · Accepted Answer

The output voltage of a summing amplifier is given by the formula Vout = -Rf*(V1/R1 + V2/R2 + V3/R3 + V4/R4). Since Rf = 10 kΩ and R1 = R2 = R3 = R4 = 40 kΩ, the gain for each input is 10kΩ/40kΩ = 0.25. Therefore, the output voltage is the sum of the inputs multiplied by 0.25, which is the average of the four input voltages.

A Summing Amplifier Has the Following Values: Rf = 10