Electronic Devices and Circuits Questions and Answers – Effect of Finite Open-Loop gain and Bandwidth on Circuit Performance

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers focuses on “Effect of Finite Open-Loop gain and Bandwidth on Circuit Performance”.

1. An internally compensated op amp is specified to have an open-loop dc gain of 106 dB and a unity gain bandwidth of 3 MHz. Find fb and the open-loop gain at fb.
a) 15Hz and 103 db
b) 30Hz and 103 db
c) 15 Hz and 51.5 db
d) 30 Hz and 51.5 db

Explanation: Use the equations below.

2. A single-pole model has __________ db/decade roll-off of the gain.

Explanation: It is a standard characteristic of a single-pole model.

3. Single-pole model is also known as
a) Frequent pole
b) Stable pole
c) Dominant pole
d) Responsive pole

Explanation: Single-pole model is also called dominant pole.

4. An op amp having a 106-dB gain at dc and a single-pole frequency response with ft = 2 MHz is used to design a non-inverting amplifier with nominal dc gain of 100. The 3-dB frequency of the closed-loop gain is
a) 10 kHz
b) 20 kHz
c) 30 kHz
d) 40 kHz

Explanation:
Use the equation below to obtain a frequency response curve and proceed further.

5. An internally compensated op amp has a dc open-loop gain of 106 V/V and an AC open-loop gain of 40 dB at 10 kHz. Estimate its gain–bandwidth product and its expected gain at 1 kHz.
a) 0.1 MHz and -60 db
b) 10 MHz and -60 db
c) 10 MHz and 60 db
d) 1 MHz and 60 db

Explanation: Use the following results.

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6. An inverting amplifier with nominal gain of −20 V/V employs an op amp having a dc gain of 104 and a unity-gain frequency of 106 Hz. What is the 3-dB frequency f3dB of the closed-loop amplifier?
a) 2π 23.8 kHz
b) 2π 47.6 kHz
c) 2π 71.4 kHz
d) 2π 95.2 kHz

Explanation:

7. cascading two identical amplifier stages, each having a low-pass STC frequency response with a 3dB frequency f1, results in an overall amplifier with a 3dB frequency given by
a) √(√2+1) f1
b) √(√3-1) f1
c) √(√2-1) f1
d) √(√3+1) f1

Explanation:

8. Find the ft required for internally compensated op amps to be used in the implementation of the closed loop amplifiers with dc gain of +100 V/V and 3db bandwidth of 100kHz?
a) 1 kHz
b) 10 kHz
c) 100 kHz
d) 1 MHz

Explanation: None

9. A particular op amp, characterized by a gain–bandwidth product of 20 MHz, is operated with a closed-loop gain of +100 V/V. What 3-dB bandwidth results? At what frequency does the closed-loop amplifier exhibit a −6° phase shift?
a) 21 kHz
b) 31.5 kHz
c) 42 kHz
d) 52.5 kHz

Explanation:

10. Find the ft required for internally compensated op amps to be used in the implementation of the closed loop amplifiers with dc gain of -2 V/V and 3db bandwidth of 10 MHz?
a) 7.5 MHz
b) 15 MHz
c) 22.5 MHz
d) 30 MHz

Explanation: -R2R1 = -2VV
f3db = 10 MHZ ft = 10 MHZ(2 + 1) = 30 MHZ.

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