Question

An inverting amplifier with gain 1 have different input voltage: 1.2v,3.2v and 4.2v. Find the output voltage?

(a) 4.2v

(b) 8.6v

(c) -4.2v

(d) -8.6v

The question was asked in a national level competition.

The above asked question is from Summing, Scaling & Averaging Amplifier topic in section Operational Amplifier Applications of Linear Integrated Circuits

Answer 1

Accurate option is (d) -8.6v

Get the lowdown with: When the gain of the inverting summing amplifier gain is 1 then, the internal resistors and feedback resistors have the same value. So, the output is equal to the negative sum of all input voltages.

VO= -(Va+Vb+Vc) =-(1.2+3.2+4.2)= -8.6v.