For the summing amplifier discussed, the circuit gain is set to which value?

For the summing amplifier discussed, the circuit gain is set to which value?

• A. 2
• B. 4
• C. 1
• D. 0

Answer: (B)

In a summing amplifier, each input is scaled by the ratio of the feedback resistor to its input resistor, and the total output is the negative sum of those scaled inputs. If the resistor values are chosen so that the feedback resistor is four times the input resistor for each path, the magnitude of the gain is four. That means the output will be inverted and equal to -4 times the sum of the input voltages (for equal input resistors). So the circuit gain in magnitude is four.

In a summing amplifier, each input is scaled by the ratio of the feedback resistor to its input resistor, and the total output is the negative sum of those scaled inputs. If the resistor values are chosen so that the feedback resistor is four times the input resistor for each path, the magnitude of the gain is four. That means the output will be inverted and equal to -4 times the sum of the input voltages (for equal input resistors). So the circuit gain in magnitude is four.