This set of Linear Integrated Circuit Problems focuses on “Summing, Scaling & Averaging Amplifier – 2”.
1. 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
Explanation: In non-inverting averaging amplifier, the non-inverting input voltage is the average of all inputs, with a positive sign.
2. Expression for output voltage of non-inverting summing amplifier with five input voltage?
a) Vo = 5×( Va + Vb+ Vc+ Vd+ Ve)
b) Vo = [1+( Rf/R1)]× ( Va + Vb+ Vc+ Vd+ Ve)
c) Vo = Va + Vb+ Vc+ Vd+ Ve
d) Vo = ( Va + Vb+ Vc+ Vd+ Ve) /5
Explanation: The output voltage of non-inverting summing amplifier is (1+ ( Rf / R1 )) times the average of all input voltages in the circuit.
Since there are five input voltages => (1+ ( Rf / R1 )) =5
Therefore, Vo = 5×( Va + Vb+ Vc+ Vd+ Ve) /5
=> Vo = (Va + Vb+ Vc+ Vd+ Ve).
Explanation: Using the superposition theorem the voltage V1 at non-inverting terminal is V1 = Va/4 + Vb/4+ Vc/4+ Vd/4 = [Va + Vb+ Vc+ Vd] /4 = [4+(-3v)+6v+(-1v) ] /4 = 1.5v.
4. If the gain of a non-inverting averaging amplifier is one, determine the input voltages if the output voltage, if the output voltage is 3v?
a) V1 =6v ,V2=3v and V3=2v
b) V1 =9v ,V2=5v and V3=-4v
c) V1 =8v ,V2=-6v and V3=1v
d) V1 =7v ,V2=4v and V3=-3v
Explanation: As the output voltage = Average of all input voltage = sum of input voltage /3
∴ sum of input voltage =3×3=9.
From the given option, the combination of input voltage 7v, 4v and -3v gives the value 9v.
5. In the circuit shown, supply voltage = ±15v, Va= +3v , Vb= -4v , Vc= +5v, R= R1= 1kΩ and RF= 2kΩ. 741 op-amp has A= 2×105 and R1= 10kΩ. Determine the output voltage internal resistance of the circuit?
a) Vo ≅3v , RiF=6.67MΩ
b) Vo ≅3v , RiF= 7MΩ
c) Vo ≅3v , RiF=9.2MΩ
d) Vo ≅3v , RiF= 3.5MΩ
Explanation: The output voltage Vo= [1 + (RF/R1)] × [ (Va+Vb+Vc/3)] = [1+(2kΩ/1kΩ)] ×[(3-4+5)/3]= 2.67 ≅ 3v.
Internal resistance of circuit, RiF =R i [A×R1/ (R1+ RF)] = 100Ω×[(200000×1kΩ)/(1kΩ+2kΩ)] => RiF= 6.67 MΩ.
6. Find the type of amplifier that cannot be constructed in differential configuration?
a) Summing amplifier
b) Scaling amplifier
c) Averaging amplifier
Explanation: In differential op-amp configuration, an amplifier produces sum or difference between two input terminals of op-amp. So, averaging is not possible in this type of configuration.
7. Calculate the output voltage, when a voltage of 12mv is applied to the non-inverting terminal and 7mv is applied to inverting terminal of a subtractor.
Explanation: Output voltage of a subtractor Vo = Vnon-inverting terminal – Vinverting terminal = 12mv-7mv =5mv.
8. Find the differential amplifier configured as a subtractor from the given circuit.
Explanation: A basic differential amplifier is used as a subtractor when all the external resistors are equal in value.
The output voltage, Vo= -(R/R)×(Va -Vb)
Vo= (Va -Vb). Hence the circuit is called as subtractor.
9. How many additional sources are connected to each input terminal to obtain an eight input summing amplifier?
Explanation: An eight input summing amplifier can be constructed using basic differential amplifier, if six additional input sources are used by connecting three input sources to inverting and non-inverting input terminal through resistors.
Explanation: The output voltage for summing amplifier is given Vo =-Va -Vb +Vc +Vd =3-4+6+5 =4v.
11. The output voltage of a summing amplifier is equal to (assume sum of input voltage as Vn )
a) Vn (non-inverting terminal)+ Vn (inverting terminal)
b) Vn (non-inverting terminal)+ (-Vn (inverting terminal)
c) -Vn (non-inverting terminal)+ (-Vn (inverting terminal)
d) -Vn (non-inverting terminal)+ Vn (inverting terminal)
Explanation: The output voltage of summing amplifier is equal to sum of the input voltage applied to the non-inverting terminal plus the negative sum of the input voltage applied to the inverting terminal.
Sanfoundry Global Education & Learning Series – Linear Integrated Circuits.
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