Operational Amplifier Fundamentals Unit 6 – The Noninverting Summing Amplifier
In this circuit, gain equals 1 + (R4/R3) and cannot be equal to or less than 1.
Output voltage (VO) equals VA x [1 + (R4/R3)].
If R1 equals R2, VA equals (V1 + V2)/2. Therefore, the circuit applies the gain factor
[1 + (R4/R3)] to the average of the input voltages.
VO = (V1 + V2)/2 x [1 + (R4/R3)]
= VA x [1 + (R4/R3)]
In a noninverting summing amplifier, VD is 0V when U1 is not saturated. When VD is greater
than 0V, U1 is saturated.
VA can be any value that when multiplied by the circuit gain factor does not drive U1 into
saturation.
NEW TERMS AND WORDS
noninverting summing amplifier - an op amp configuration that algebraically combines input
voltages and does not invert the sum voltage polarity.