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.
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.