300+ Active Filter MCQ – Objective Question Answer for Active Filter Quiz

51. Which filter attenuates any frequency outside the passband?

A. Band-pass filter
B. Band-reject filter
C. Band-stop filter
D. All of the mentioned

Answer: A

A band-pass filter has a passband between two cut-off frequencies fH and fL. So, any frequency outside this passband is attenuated.

 

52. Narrow band-pass filters are defined as

A. Q < 10
B. Q = 10
C. Q > 10
D. None of the mentioned

Answer: C

Quality factor (Q) is the measure of selectivity, meaning the higher the value of Q, the narrower its bandwidth.

 

53. A band-pass filter has a bandwidth of 250Hz and a center frequency of 866Hz. Find the quality factor of the filter?

A. 3.46
B. 6.42
C. 4.84
D. None of the mentioned

Answer: A

Quality factor of band-pass filter

Q =fc/bandwidth

= 566/250=3.46.

 

54. Find the center frequency of wide band-pass filter

A. fc= √(fh  × fL)
B. fc= √(fh +fL)
C. fc= √(fh -fL)
D. fc= √(fh /fL)

Answer: A

In a wide band-pass filter, the product of high and low cut-off frequency is equal to the square of the center frequency

i.e. ( fc)2 =fH × fL

=> fc= √(fh × fL).

 

55. Find out the voltage gain magnitude equation for the wide band-pass filter.

A. AFt × ( f/fL)/√[(1+(f/fh)2] × [1+(f/fL)2].

B. AFt/ √{[1+(f/fh)2] × [1+(f/fL)2]}

C. AFt/ √{[1+(f/fh)2]/[1+(f/fL)2]}

D. [AFt/(f/fL)]/ √{[1+(f/fh)2]/[1+(f/fL)2]}

Answer: A

The voltage gain magnitude of the band-pass filters is equal to the product of the voltage gain magnitudes of high pass and low pass filters.

 

56. When a second-order high pass filter and second-order low pass sections are cascaded, the resultant filter is a

A. ±80dB/decade band-pass filter
B. ±40dB/decade band-pass filter
C. ±20dB/ decade band-pass filter
D. None of the mentioned

Answer: B

When a second-order high pass filter and second-order low pass sections are cascaded, the resultant filter is a ±40dB/decade band-pass filter.

The order of the band-pass filter depends on the order of the high pass and low pass filter sections.

 

57. Find the voltage gain magnitude of the wide band-pass filter?
Where total passband gain is=6, input frequency = 750Hz, Low cut-off frequency =200Hz and high cut-off frequency=1khz.

A. 13.36 dB
B. 12.25 dB
C. 11.71 dB
C. 14.837dB

Answer: D

Voltage gain of the filter,

|VO/Vin|=[AFt × (f/fL)]/{√[1+(f/fL)2] × [1+f/fL)2]}

=[6 × (750/20)]/√{[1+(750/200)2] × [1+(750/200)2]}

=22.5/√(15.6 × 1.56) =5.519.

|VO/Vin|= 20log(5.519) =14.837dB.

 

58. Compute the quality factor of the wide band-pass filter with high and low cut-off frequencies equal to 950Hz and 250Hz.

A. 0.278
B. 0.348
C. 0.696
D. 0.994

Answer: C

Quality factor

Q=√(fh × fL)/(fh-fL)

= √(950Hz × 250Hz)/(9950Hz-250Hz) =0.696.

 

59. The details of low pass filter sections are given as fh =10kHz, AF= 2, and f=1.2kHz. Find the voltage gain magnitude of the first-order wide band-pass filter, if the voltage gain magnitude of the high pass filter section is 8.32dB.

A. 48.13dB
B. 10.02dB
C. 14.28dB
D. 65.99dB

Answer: C

|VO/Vin|(high pass filter)

= 8.32dB=10(8.32/20) =2.606.

Therefore, the voltage gain of wide band-pass filter |VO/Vin|

= AFt × (f/fL)/√[1+(f/fh)2)] × [1+(f/fL)2)]

={Af/√[(1+(f/fh)2]} × {(Af × f/fL)/√[1+(f/fL)2]}

=Aft /√[1+(f/fh)2] × (2.606)

= [2/√(1+(1.2kHz/10kHz)2] × ( 2.606)

= 1.986 × 2.606 =5.17

=20log × (5.17) =14.28dB.

 

60. The quality factor of a wide band-pass filter can be

A. 12.6
B. 9.1
C. 14.2
D. 10.9

Answer: B

A wide band-pass filter has a quality factor of less than 10.

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