# Electronic Devices and Circuits Questions and Answers – The Ideal Operational Amplifiers

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “The Ideal Operational Amplifiers”.

1. What is the minimum number of terminals required in an IC package containing four operational amplifiers (quad op amps)?
a) 12
b) 13
c) 14
d) 15

Explanation: The minimum no of pins required by dual-op-amp is 8. Each op-amp has 2 input terminals(4 pins) and one output terminal(2 pins). Another 2 pins are required for power.
Similarly, The minimum no of pins required by dual-op-amp is 14: 4*2 + 4*1 + 2 = 14.

2. Which of the following is not a property of an ideal operational amplifier?
a) Zero input impedance
b) Infinite bandwidth
c) Infinite open loop gain
d) Zero common-mode gain or conversely infinite common mode-rejection.

Explanation: An ideal operational amplifier does not has a zero input impedance.

3. In an ideal op amp the open-loop gain is 103. The op amp is used in a feedback circuit, and the voltages appearing at two of its three signal terminals are measured as v2 = 0V and v3 = 2V where it is assumed that v1 and v2 are input terminals and v3 is the output terminal. The value of the differential (vd) and common-mode (vcm)signal is
a) Vd = 2 mV and vcm = 1 mv
b) Vd = 2 mV and vcm = -1 mV
c) Vd = 2 mV and vcm = 2mV
d) Vd = 2 mV and vcm = -2mV

Explanation: Vc = 0.5(V1 + V2) and
Vd = V2 – V1.

4. Consider the figure given below. Known that vo = 4V and vi = 2V, determine the gain for the op amp assuming that it is ideal except for the fact that it has finite gain a) 1001
b) 2002
c) 3003
d) 4004

Explanation: The Voltage at the positive input has to be -3.000v, vi = -3.020v
A = vo / vi – vr = -2 / -3.020 -(-3) = 100.

5. Which of the following is not a terminal for the operational amplifier?
a) Inverting terminal
b) Non-inverting terminal
c) Output terminal
d) None of the mentioned

Explanation: There are three terminals for the operational amplifier.

6. Operational amplifiers are
a) Differential input and single-ended output type amplifier
b) Single-ended input and single-ended output type amplifier
c) Single-ended input and differential output type amplifier
d) Differential input and differential output type amplifier

Explanation: It is another way to refer to op amps based on its terminal characteristics.

7. Express the input voltages v1 and v2 in terms of differential input (vd) and common-mode input(vc). Given v2 > v2.
a) Vd = V1 – V2, Vc = 0.5(V1 + V2)
b) Vd = V2 – V1, Vc = V1 + V2
c) Vd = V1 – V2, Vc = V1 + V2
d) Vd = V2 – V1, Vc = 0.5(V1 + V2)

Explanation: This is the correct mathematical representation.

8. What is the minimum number of pins for a dual operational amplifier IC package?
a) 4
b) 6
c) 8
d) 10

Explanation: The minimum no of pins required by dual-op-amp is 8. Each op-amp has 2 input terminals(4 pins) and one output terminal(2 pins). Another 2 pins are required for power.

9. For an ideal operational amplifier (except for the fact that it has finite gain) one set of the value for the input voltages (v2 is the positive terminal v1 is the negative terminal) and output voltage (v0) as determined experimentally is v1= 2.01V, v2=2.00V and v0= -0.99V. Experiment was carried with different values of input and output voltages. Which of the following is not possible considering experimental error?
a) v1= 1.99V, v2= 2.00V, v0 = 1.00V
b) v1= 1.00V, v2= 1.00V, v0 = 0V
c) v1= 1.00V, v2= 1.10V, v0 = 10.1V
d) v1= 0.99V, v2= 2.00V, v0 = 1.00V

Explanation: Only option d does not satisfies the mathematical relation between the given quantities.

10. What are the units of slew rate?
a) Second/Volt
b) Volt/second
c) It is a ratio, no units
d) Ohm/second

Explanation: These units are obtained from the definition of the term slew rate.

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