Linear Integrated Circuit Multiple Choice Questions on “Summing, Scaling & Averaging Amplifier – 1”.
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
Answer: B
Clarification: In 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
Answer: A
Clarification: If the internal resistors of the circuit is same i.e Ra=Rb=Rc=Rd=R (since there are four internal resistor)
Then, the output voltage for inverting amplifier is given as Vo= -(Rf/R)×(Va +Vb+Vc+Vd).
3. 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
Answer: D
Clarification: 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
Answer: C
Clarification: The weighted amplifier is also called as 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
Answer: A
Clarification: 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, output voltage Vo = -{[(RF/Ra) Va] +[(RF/Rb) Vb]+[(RF/Rc) Vc]}.
6. An amplifier in which the output voltage is equal to average of input voltage?
A. Summing amplifier
B. Weighting amplifier
C. Scaling amplifier
D. Averaging amplifier
Answer: D
Clarification: 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
Answer: B
Clarification: In an averaging amplifier, the gain by which each input is amplified must be equal to lower number of input.
=> 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 voltage applied to the inverting input terminal of averaging amplifier. Determine the output voltage?
A. -5v
B. -10v
C. -15v
D. -20v
Answer: A
Clarification: 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
Answer: D
Clarification: 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.
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