Operational Amplifier Fundamental MCQ [Free PDF] - Objective Question Answer for Operational Amplifier Fundamental Quiz

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

The maximum possible output offset voltage is

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.

26. Input bias current is defined as

A. Average of two input bias current
B. Summing of two input bias current
C. Difference of two input bias current
D. Product of two input bias current

Answer: A

Input bias current is the average of two input bias currents flowing into the non-inverting and inverting input of an op-amp.

27. Although the value of input bias current is very small, it causes

A. Output voltage
B. Input offset voltage
C. Output offset voltage
D. All of the mentioned

Answer: C

Even a very small value of input bias current can cause a significant output offset voltage in circuits using relatively large feedback resistors.

28. The formula for output offset voltage of an op-amp due to input bias current

A. V_OIB= R_F*I_B
B. V_OIB= (R_F+R₁)/I_B
C. V_OIB= (1+R_F)*I_B
D. V_OIB= [1+(R_F/R₁)]*I_B

Answer: A

The formula for output offset voltage of an op-amp due to input bias current is V_OIB = R_F*I_B.

29. Find the input bias current for the circuit given below

A. 10mA
B. 2mA
C. 5mA
D. None of the mentioned

Answer: C

Input bias current

I_B=(I_B1+ I_B2)/2

=> I_B =(4mA+6mA/2 = 5mA.

30. Mention a step to reduce the output offset voltage caused due to input bias current?

A. Use small feedback resistor and resistance at the input terminal
B. Use small feedback resistors
C. Reduce the value of load resistors
D. None of the mentioned

Answer: B

Since the output offset voltage is proportional to the feedback resistor and input bias current. The amount of V_OIB can be reduced by reducing the value of the feedback resistor.

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