# Summing Scaling and Averaging Amplifier MCQ [Free PDF] – Objective Question Answer for Summing Scaling and Averaging Amplifier Quiz

1. In which amplifier the output voltage is equal to the negative sum of all the inputs?

A. Averaging amplifier
B. Summing amplifier
C. Scaling amplifier
D. All of the mentioned

In the summing amplifier, the output voltage is equal to the sum of all input. Since the total input is a sum of negative input, the amplifier is an inverting summing amplifier.

2. Determine the expression of output voltage for inverting summing amplifier consisting of four internal resistors? (Assume the value of internal resistors to be equal)

A. Vo = -(Rf/R )×(Va +Vb+Vc+Vd)
B. Vo = (RF/R)×(Va +Vb+Vc+Vd)
C. Vo = (R/ RF)×(Va +Vb+Vc+Vd)
D. None of the mentioned

If the internal resistors of the circuit are the same i.e

Ra=Rb=Rc=Rd=R (since there are four internal resistors)

Then, the output voltage for inverting amplifier is given as

Vo= -(Rf/R)×(Va +Vb+Vc+Vd).

3. An inverting amplifier with gain 1 has 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

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.

4. In which type of amplifier, the input voltage is amplified by a scaling factor

A. Summing amplifier
B. Averaging amplifier
C. Weighted amplifier
D. Differential amplifier

The weighted amplifier is also called a scaling amplifier. Here each input voltage is amplified by a different factor i.e. Ra, Rb and Rc are different in values ( which are the input resistors at each input voltage).

5. An inverting scaling amplifier has three input voltages Va, Vb and Vc. Find it output voltage?

A. VO= – {[(RF/Ra)×Va] +[(RF/Rb)×Vb]+[(RF/Rc)×Vc]}
B. VO= – [(RF/Ra)+(RF/Rb)+(RF/Rc)]×[( Va +Vb+Vc)].
C. VO = – {[(Ra/RF)×Va] +[(Rb/RF)×Vb]+[(Rc/RF)×Vc]}
D. None of the mentioned

Since three input voltages are given assume the input resistors to be Ra, Rb, and Rc. In a scaling amplifier, the input voltages are amplified by a different factor

=> ∴ RF/Ra ≠ RF/Rb ≠ RF/Rc

Therefore, the output voltage

Vo = -{[(RF/Ra) Va] +[(RF/Rb) Vb]+[(RF/Rc) Vc]}.

6. An amplifier in which the output voltage is equal to an average input voltage?

A. Summing amplifier
B. Weighting amplifier
C. Scaling amplifier
D. Averaging amplifier

An averaging amplifier can be used as an averaging circuit, in which the output voltage is equal to the average of all the input voltages.

7. Find out the gain value by which each input of the averaging amplifier is amplified? ( Assume there are four inputs)

A. 0.5
B. 0.25
C. 1
D. 2

In an averaging amplifier, the gain by which each input is amplified must be equal to the lower number of inputs.

=> RF /R =1/n , where n=number of inputs

∴ RF /R=1/4 = 0.25 (Four inputs)

So, each input in the averaging amplifier must be amplified by 0.25.

8. 3v, 5v, and 7v are the three input voltages applied to the inverting input terminal of the averaging amplifier. Determine the output voltage?

A. -5v
B. -10v
C. -15v
D. -20v

The output voltage,

Vo = -[(Va+Vb+Vc)/3]

= -[(3+5+7)/3] =-5v.

9. The following circuit represents an inverting scaling amplifier. Compute the value of RoM and VO?

A. VO = -0.985v ; RoM = 111.11Ω
B. VO = -2.567v ; RoM = 447.89Ω
C. VO = -1.569v ; RoM = 212.33Ω
D. VO = -1.036v ; RoM = 320.56Ω

VO = – {[(RF/Ra)×Va]+[(RF/Rb)×Vb] + [(RF/Rc)×Vc]}

= – {[(10kΩ/1kΩ)×3.3mv] + [(10kΩ/1.25kΩ)×5mv] +

[(10kΩ/820Ω)×7.9mv]} = -1.036v.

RoM = [Ra||Rb||Rc||RF]

= [(Ra×Rb)/(Ra+ Rb)] || [(Rc×RF)/( Rc+ RF)] =

[(1kΩ×1.25kΩ)/(1kΩ+1.25kΩ)] || [(820Ω×10kΩ)/(820Ω+10kΩ)] =

555.55||757.85

=[(555.55 ×757.85)/(555.55+757.85)] = 320.56Ω.

10. Which type of amplifier has output voltage equal to the average of all input voltages?

A. Inverting averaging amplifier
B. Non-inverting averaging amplifier
C. Non-inverting summing amplifier
D. Inverting scaling amplifier