# Operational Amplifier Internal Circuit – 3

This set of Signals & Systems Multiple Choice Questions & Answers (MCQs) focuses on “Operational Amplifier Internal Circuit – 3″.

1. In practical application of current mirror, early voltage is assumed to be
a) Infinite
b) Zero
c) Unity
d) None of the mentioned

2. A widlar current source is used
a) to get low value of current
b) to get high value of CMRR
c) to get low voltage of gain
d) to get high value of Output

3. Determine the early voltage, if the output resistance is 2.5×2kΩ and input current is 2mA
a) 9.8v
b) 5.6v
c) 7.8v
d) 10v

4. What will be the value of emitter resistance in widlar current source for output current 10mA, having Iref=2.7A
a) 67/(1+1/β)Ω
b) 13/(1+1/β)Ω
c) 14/(1+1/β)Ω
d) 1.36/(1+1/β)Ω

5. If the reference and collector current are 0.539mA and 0.49mA respectively, how many transistors are used in current repeater circuit? (Assume β =150)
a) 11
b) 14
c) 10
d) 8

6. The requirements for a good current source is the one in which, (Take Output current – IO and Output resistance – rO )
a) IO independent upon current gain and should be low
b) rO should be very high
c) IO in the circuit should be low
d) IO independent upon current gain and rO should be very high

7. A current repeater having identical transistor has collector current, IC1 =0.39mA. Find IC2,IC4& IC6
a) 0.39mA, 0.39mA, 0.78mA
b) 0.78mA, 0.39mA, 0.39mA
c) 0.39mA, 0.78mA, 0.39mA
d) None of the mentioned

8. For the current repeater shown in the circuit, determine IC4 value, Where β = 75.

a) 0.035mA
b) 0.028mA
c) 0.04mA
d) 0.052mA

9. Which current source exhibits a very high output resistance?
a) Simple current mirror
b) Wilson current mirror
c) Widlar current mirror
d) All of the mentioned

10. To increase the input resistance in differential amplifier, replace the transistor by
a) Current mirror
b) Current repeater
c) Darlington pair
d) All of the mentioned

11. Determine the amount of shift happens in level shifter?
a) Vcc + 0.7v
b) Vcc – 0.7v
c) -0.7v
d) +0.7v

12. What will be the overall gain in Darlington circuit, if the individual transistor gain is 200?
a) 10000
b) 40000
c) 8000
d) 1000

13. What is the drawback in using Darlington pair in differential amplifier?
a) Large current gain
b) Output current in milli ampere
c) Gain is proportional to load resistor
d) High offset voltage

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