# Linear Integrated Circuit Questions and Answers – Active Filters – 1

This set of Linear Integrated Circuit Multiple Choice Questions & Answers (MCQs) focuses on “Active Filters – 1”.

1. An electrical filter is a
a) Phase-selective circuit
b) Frequency-selective circuit
c) Filter-selective circuit
d) None of the mentioned

Explanation: An electric filter is often a frequency selective circuit that passes a specified band of frequencies and blocks or alternates signal of frequencies outside this band.

2. Filters are classified as
a) Analog or digital
b) Passive or active
d) All of the mentioned

Explanation: Filters are classified based on the design technique (analog or digital), elements used for construction (active or passive) and operating range (audio or radio frequency).

3. Why inductors are not preferred for audio frequency?
a) Large and heavy
b) High power dissipation
c) High input impedance
d) None of the mentioned

Explanation: At audio frequencies, inductor becomes problematic, as the inductors become large, heavy and expensive.

4. The problem of passive filters is overcome by using
a) Analog filter
b) Active filter
c) LC filter
d) A combination of analog and digital filters

Explanation: The active filters enclose as a capacitor in the feedback loop and avoid using inductors, this way inductorless active filter are obtained.

5. What happens if inductors are used in low frequency applications?
a) Enhance inductor usage
b) No losses occurs
d) Low power dissipation

Explanation: For low frequency applications more number of turns of wire must be used, which in turn adds to the series resistance degrading inductor’s performance.
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6. Find out the incorrect statement about active and passive filters.
a) Gain is not attenuated in active filter
b) Passive filters are less expensive
d) Passive filters are difficult to tune or adjust

Explanation: Typically active filters are more economical than passive filters. This is because of the variety of cheaper op-amp and the absence of inductor’s.

7. What are the most commonly used active filters?
a) All of the mentioned
b) Low pass and High pass filters
c) Band pass and Band reject filters
d) All-pass filters

Explanation: All the mentioned filters use op-amp as active element and capacitors & resistors as passive elements.

8. Choose the op-amp that improves the filter performance.
a) µA741
b) LM318
c) LM101A
d) MC34001

Explanation: LM318 is a high speed op-amp that improves the filter’s performance through increased slew rate and higher unity gain-bandwidth.

9. Ideal response of filter takes place in
a) Pass band and stop band frequency
b) Stop band frequency
c) Pass band frequency
d) None of the mentioned

Explanation: The ideal response indicates the practical filter response and it lies within the pass band frequencies.

10. Find out the low pass filter from the given frequency response characteristics.
a)

b)

c)

d)

Explanation: A low pass filter has a constant gain from 0Hz to high cut-off frequency fH.

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