This set of Electronic Devices & Circuits Multiple Choice Questions & Answers (MCQs) focuses on “DC Imperfections in Operational Amplifiers”.

(Q1 & Q.2) Consider an inverting amplifier with a nominal gain of 1000 constructed from an op amp with an input offset voltage of 3 mV and with output saturation levels of ±10 V. If the effect of V_{Os}(input offset voltage) is nulled at room temperature (25_{0}C), how large an input can one now apply if:

1. The circuit is to operate at a constant temperature?

a) 8.5 mV

b) 9 mV

c) 9.5 mV

d) 10 mV

2. The circuit is to operate at a temperature in the range 0°C to 75°C and the temperature coefficient of V_{OS} is 10 μV/°C?

a) 8.5 mV

b) 9 mV

c) 9.5 mV

d) 10 mV

3. Consider an inverting amplifier with a nominal gain of 1000 constructed from an op amp with an input offset voltage of 3 mV and with output saturation levels of ±10 V. What is (approximately) the peak sine-wave input signal that can be applied without output clipping?

a) 7 mV

b) 10 mV

c) 13 mV

d) 9mV

4. One of the DC imperfections of the amplifiers are dc offset voltage which is

a) Existence of output signal even when the common mode signal is zero

b) Existence of common mode signal causing zero output signal

c) Existence of output signal even when the differential signal is zero

d) Existence of differential signal causing zero output signal

5. Consider the circuit shown below which reduces the impact of the input bias current. If I_{B1} = I_{B2} = Input bias current, then determine the value of R_{3} so that the output voltage (v_{0}) is not impacted by the input bias current.

a) (R1 R2)/(R1+R2)

b) (R1 R2)/(R1-R2)

c) R1-(R1 R2)/(R1+R2)

d) R2- (R1 R2)/(R1+R2)

6. For the amplifier shown determine the value of the bias current (I_{b}) and input offset current (I_{o}) respectively.

a) I_{b} = I_{B1} + I_{B2} I_{o} = I_{B1} – I_{B2}

b) I_{b} = I_{B1} + I_{B2} I_{o} = | I_{B1} – I_{B2} |

c) I_{b} = 0.5(I_{B1} + I_{B2}) I_{o} = | I_{B1} – I_{B2 }|

d) I_{b} = 0.5(I_{B1} + I_{B2}) I_{o} = I_{B1} – I_{B2}

7. Consider an inverting amplifier circuit designed using an op amp and two resistors, R_{1} = 10 kΩ and R_{2} = 1 MΩ. If the op amp is specified to have an input bias current of 100 nA and an input offset current of 10 nA, find the output dc offset voltage resulting.

a) 0.1 mV

b) 1 mV

c) 10 mV

d) 100 mV

(Q.8-Q.10) Consider a Miller integrator with a time constant of 1ms and an input resistance of 10 kΩ. Let the op amp have V_{OS} (offset voltage) = 2 mV and output saturation voltages of ±12 V.

8. Select the largest possible value for a feedback resistor RF so that at least ±10 V of output signal swing remains available.

a) 10 kΩ

b) 100 kΩ

c) 1 MΩ

d) 10 MΩ

9. Assuming that when the power supply is turned on the capacitor voltage is zero, how long does it take for the amplifier to saturate?

a) 3s

b) 6s

c) 9s

d) 12s

10. What is the corner frequency of the resulting STC network?

a) 1 Hz

b) 0.16 Hz

c) 0.33 Hz

d) 0.5 Hz