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

1. Which is not the internal circuit of an operational amplifier?

A. Differential amplifier
B. Level translator
C. Output driver
D. Clamper

Answer: D

Clamper is an external circuit connected to the output of the Operational amplifier, which clamps the output to the desired DC level.

 

2. The purpose of the level shifter in the Op-amp internal circuit is to

A. Adjust DC voltage
B. Increase impedance
C. Provide high gain
D. Decrease input resistance

Answer: A

The gain stages in Op-amp are directly coupled. So, a level shifter is used for the adjustment of the DC level.

 

3. How a symmetrical swing is obtained at the output of Op-amp?

A. Providing amplifier with negative supply voltage
B. Providing amplifier with positive voltage
C. Providing amplifier with positive& negative voltage
D. None of the mentioned

Answer: C
For example, consider a single voltage supply +15v. During a positive half cycle, the output will be +5v and -10v during the negative half cycle.

Therefore, the maximum peak to peak output swing, -5v (-10v) = -15v (Asymmetrical swing).

So, to get a symmetrical swing both positive and negative supply voltage with bias point fixed suitably is required.

 

4. What is the purpose of the differential amplifier stage in the internal circuit of Op-amp?

A. Low gain to the differential mode signal
B. Cancel difference mode signal
C. Low gain to the common-mode signal
D. Cancel common-mode signal

Answer: D

Any undesired noise, common to both of the input terminals is suppressed by a differential amplifier.

 

5. Which of the following is not preferred for the input stage of Op-amp?

A. Dual Input Balanced Output
B. Differential Input Single-ended Output
C. Cascaded DC amplifier
D. Single Input Differential Output

Answer: C

Cascaded DC amplifier suffers from a major problem of drift of the operating point, due to temperature dependency of the transistor.

 

6. What will be the emitter current in a differential amplifier, where both the transistor are biased and matched? (Assume current to be IQ)

A. IE = IQ/2
B. IE = IQ
C. IE = (IQ)2/2
D. IE = (IQ)2

Answer: A
Due to the symmetry of the differential amplifier circuit, current IQ divides equally through both transistors.

 

7. From the circuit, determine the output voltage (Assume αF=1)

From the circuit, determine the output voltage (Assume αF=1)

A. VO1=3.9v , VO2=12v
B. VO1=12v , VO2=3.9v
C. VO1=12v , VO2=0v
D. VO1=3.9v , VO2=-3.9v

Answer: B

The voltage at the common emitter ‘E’ will be -0.7v, which makes Q1 off and the entire current will flow through Q2.

⇒ VO1 = VCC VO2 = VCC-αF×IQ×RC,

⇒ VO1 = 12v , VO2 = 12v-1×3mA × 2.7k = 3.9v.

 

8. At what condition does differential amplifier function as a switch

A. 4VT < Vd < -4VT
B. -2VT ≤ Vd ≤ 2VT
C. 0 ≤ Vd < -4VT
D. 0 ≤ Vd ≤ 2VT

Answer: A
For Vd > 4VT, the output voltage is VO1 = VCC, VO2= VCC-αF IQRC. Therefore, a transistor Q1 will be ON and Q2 will be OFF. Similarly for Vd> -4VT, both transistors Q2 & Q1 will be ON.

 

9. For Vd > ±4VT, the function of the differential amplifier will be

A. Switch
B. Limiter
C. Automatic gain control
D. Linear Amplifier

Answer: B

At this condition, the input voltage of the amplifier is greater than ±100mv and thus acts as a limiter.

 

10. Change in value of common-mode input signal in differential pair amplifier make

A. Change in voltage across the collector
B. Slight change in collector voltage
C. Collector voltage decreases to zero
D. None of the mentioned

Answer: A

In a differential amplifier due to symmetry, both transistors are biased and matched. Therefore, the Voltage at each collector will be the same.

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