Input Offset Voltage MCQ [Free PDF] - Objective Question Answer for Input Offset Voltage Quiz

1. What makes the output voltage equal to zero in practical op-amp?

A. Input offset voltage
B. output offset voltage
C. Offset minimizing voltage
D. Error voltage

Answer: A

The input offset voltage is the differential input voltage that exists between two input terminals of an op-amp without any external input and forces the output voltage to zero.

2. What happens due to a mismatch between two input terminals in an op-amp?

A. Input offset voltage
B. Output offset voltage
C. Bothe the input and output offset voltage
D. None of the mentioned

Answer: B

The input offset voltage in op-amp force the output voltage to zero due to the mismatch between two input terminal, there will be voltage produced at the output, and this voltage is called output offset voltage.

3. Define the polarity of the output offset voltage in a practical op-amp?

A. Positive polarity
B. Negative polarity
C. Positive or negative polarity
D. None of the mentioned

Answer: C

The output offset voltage is a DC voltage, it may be positive or negative in polarity depending on whether the potential difference between two input terminals is positive or negative.

4. The input offset voltage of 741 op-amps has an absolute maximum value of 6mv, which means

A. Minimum difference between input terminals in 741 op-amps can be large as 6mv DC
B. Minimum difference between input terminals in 741 op-amps can be large as 6mv AC
C. Maximum difference between input terminals in 741 op-amps can be large as 6mv DC
D. Maximum difference between input terminals in 741 op-amps can be large as 6mv AC

Answer: C

Given that, the absolute maximum value for a 741 is V_io= 6mv. Therefore, the voltage at the non-inverting input terminal may differ from that at the inverting input terminal by as much as 6mv dc. Also, the output offset voltage is a DC voltage and it cannot be an AC voltage.

5. If three different 741 op-amps are taken and the corresponding output offset voltage for each of them is measured. The output voltage in these three op-amps have

A. Same amplitude and polarity
B. Different amplitude and polarity
C. Same amplitude and different polarity
D. Different amplitude and same polarity

Answer: B

Even though the op-amps are of the same type, the output voltage in these three op-amps is not of the same amplitude and polarity, because of mass production.

6. To reduce the output offset voltage V_ooT to zero

A. Input offset voltage compensating network is added at the inverting input terminal
B. Input offset voltage compensating network is added at the non-inverting input terminal
C. Input offset voltage compensating network is added at the output terminal
D. None of the mentioned

Answer: D

To reduce the V_ooT to zero, the external circuit is added at the input terminal of the op-amp which will give the flexibility of obtaining input offset voltage of proper amplitude and polarity. The input terminal can be inverting or non-inverting.

7. Which of the following op-amp does not need a compensating network?

A. 777
B. 741
C. 748
D. All of the mentioned

Answer: D

The compensating network is not needed for these op-amps because they have offset null pins.

8. What will the condition of the op-amp before applying any external input

A. Compensated
B. Biased
C. Balanced
D. Zero

Answer: C

Before applying external input to the op-amp, the output offset voltage should be reduced to zero with the help of an offset voltage compensating network. At this condition, the op-amp is said to be balanced or nulled.

9. Find Thevenin’s equivalent for resistance and voltage?

A. 1-iii, 2-ii, 3-1
B. 1-ii, 2-I, 3-iii
C. 1-I, 2-ii, 3-iii
D. 1-ii, 2-iii, 3-i

Answer: B

The maximum Thevenin equivalent resistance R_max occurs when the wiper is at the center of the potentiometer and the maximum Thevenin equivalent voltage V_max is equal to +Vcc or –Vee when the wiper is uppermost or lowest in the potentiometer.

10. What is done to compensate for the voltage, when V₁ > V₂?

A. Move the wiper towards +Vcc
B. Move the wiper towards –Vee
C. Keep the wiper at the center of the potentiometer
D. None of the mentioned

Answer: A

V₁ > V₂ implies that output offset voltage is positive. This means that V₂ should be increased until it is equal to V₁. The wiper can be moved towards +Vcc until the output offset voltage is reduced to zero.

11. Calculate the maximum Thevenin equivalent resistance, if a 10kΩ potentiometer is used?

A. 0.4kΩ
B. 5 kΩ
C. 2.5kΩ
D. 4kΩ

Answer: C

R_max= R_a/2 || R_a/2 = R_a/4.

Given potentiometer, R_a = 10kΩ

=> Therefore, R_max = 10kΩ/4 =2.5kΩ.

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12. Find the input offset voltage for the circuit shown

A. V_io = (R_b*V_max)/( R_max+ R_b+ R_c)
B. V_io = R_max/( R_max+ R_b+ R_c)
C. V_io = (R_c*V_max)/( R_max+ R_b+ R_c)
D. V_io = V_max/( R_max+ R_b+ R_c)

Answer: C

Compensating network using maximum Thevenin’s equivalent for resistance and voltage circuit is shown. Since |V₁-V₂|- V_io, the maximum value of V₂ can be equal to V_io.

13. Find the value of R_a and R_b from the circuit shown?

A. R_a =4.6kΩ ; R_b= 9kΩ
B. R_a =7.3kΩ ; R_b= 3.4kΩ
C. R_a =2.5kΩ ; R_b= 5.1kΩ
D. R_a =4kΩ ; R_b= 10kΩ

Answer: D

We know that input offset voltage, V_io =(R_c*V_max)/ R_b

=> R_b = V_max*(R_c / R_b )

= (10v/10mv)*10Ω (∵ V_io specified on the datasheet is 10mv for LM307 op-amp).

=> R_b =10000 = 10kΩ.

Since R_b > R_max let us choose R_b = 10*R_max. (Where R_max = R_a/4).

∴ R_b = (10*R_b)/4 and R_a = R_b/2.5

= 10kΩ/2.5=4kΩ.

14. Why does an op-amp without feedback is not used in linear circuit application?

A. Due to high current gain
B. Due to high voltage gain
C. Due to high output signal
D. All of the mentioned

Answer: B

In an op-amp without feedback, the voltage gain is extremely high (ideally infinite). Because of the high risk of distortion and clipping of the output signal, an op-amp in open loop configuration is not used in linear circuit applications.

15. When the input voltage is reduced to zero in a closed-loop configuration the circuit acts as

A. Inverting amplifier
B. Non-inverting amplifier
C. Inverting and non-inverting amplifier
D. None of the mentioned

Answer: C

Since the input signal voltage is reduced to zero, the internal resistance is negligibly small. The output offset voltage is expressed in terms of external resistance and the specified input offset voltage for a given op-amp.

If the non-inverting input terminal is connected to the ground, it acts as inverting op-amp and vice versa.

16. How the value of output offset voltage is reduced in closed-loop op-amp?

A. By increasing gain
B. By reducing the gain
C. By decreasing bandwidth
D. By reducing bandwidth

Answer: B

The output offset voltage is a product of gain and specified input offset voltage for a given op-amp. V_oo= A_oo*V_io. So, the value of output offset voltage can be reduced by reducing the gain value.

17. What happens if R₁>>R_F in the circuit

A. Some amount of output offset voltage is present
B. Some amount of input offset voltage is present
C. Some amount of gain voltage is present
D. All of the mentioned

Answer: A

If R₁ >>R_F, the gain A_oo≅1, which makes V_oo ≅ V_io. Thus, all op-amp circuit has some output offset voltage.

18. Determine the voltage gain for the circuit.

A. 1.1
B. 1.6
C. 1.2
D. 2.2

Answer: D

The voltage gain,

A_F={1+[R_F/( R₁+ R_c)]}

= 1+[15kΩ/(2.5kΩ+10kΩ)] = 2.2.

19. Where does the compensating network connected in an inverting amplifier.

A. Non-inverting input terminal
B. Inverting input terminal
C. Between non-inverting and output terminal
D. Between inverting and output terminal

Answer: A

The offset voltage compensating network is connected to the non-inverting terminal for the inverting amplifier and vice versa.

20. Why closed-loop differential amplifiers are difficult to null?

A. Due to compensating network
B. Due to the feedback loop
C. Due to the input offset voltage
D. None of the mentioned

Answer: A

The closed-loop differential amplifiers are more difficult to null because the use of compensating network can change the common-mode rejection mode.

21. How to achieve maximum CMRR in the given circuit?

A. R₁ = R_F
B. R_F = R₃|| R_C+ R_B and R₁= R₂
C. R₁= R₂ and R_F= R₃+ R_C
D. None of the mentioned

Answer: C

To achieve maximum CMRR in the circuit the value of R₁= R₂ and R_F= R₃+ R_C.

22. What is the advantage of the compensated differential amplifier?

A. All of the mentioned
B. Slightly complex circuit
C. Does not affect CMRR
D. Balanced op-amp

Answer: D

Since the compensated differential amplifier uses the op-amp with offset voltage null pins. The offset null circuit does not affect the CMRR.

23. The offset voltage in the voltage follower is balanced using

A. Voltage drop across the load resistor
B. Voltage drop across the feedback resistor
C. Compensating network connected to inverting input terminal
D. Compensating network connected to the non-inverting input terminal

Answer: B

The voltage drop across the feedback resistor connected to inverting input terminal is used to cancel the offset voltage in the voltage follower.

24. Find the maximum possible output offset voltage, which is caused by the input offset voltage V_io=15mv?

A. 0.075v
B. 0.75v
C. 0.75v
D. 7.5v

Answer: A

A_oo=[1+(R_F/R₁)]

=1+(10kΩ/2.5kΩ) = 5.

V_oo=5*15mv = 75mv.

25. Compute the output voltage for voltage follower with offset voltage compensating network?

A. 3.6v
B. 10.8v
C. 26v
D. 33v

Answer: B

The output voltage is given as

V_o= {1+[ R_C/( R_b+ (R_max/4))]}*V_in.

R_max=R_a/4 = 20kΩ/4 = 5kΩ.

V_o=[1+(39kΩ/(10kΩ+5kΩ))]*3v = 10.8v.

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