A. Varying
B. Fixed
C. Random
D. None of the mentioned
Answer: B
The overall gain of a higher-order filter is fixed because all the frequency-determining resistors and capacitors are equal.
12. Find the roll-off rate for 8th order filter
A. -160dB/decade
B. -320dB/decade
C. -480dB/decade
D. -200dB/decade
Answer: A
For the nth order filter the roll-off rate will be –
n×20dB/decade.
=>∴ for 8th order filter= 8×20=160dB/decade.
13. 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.
14. 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.
15. 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.
16. 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).
17. 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.
18. 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
The order of the band-pass filter depends on the order of the high pass and low pass filter sections.
19. 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.
20. 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.
21. 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.
22. 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.
23. If the gain at center frequency is 10, find the quality factor of the narrow band-pass filter
A. 1
B. 2
C. 3
D. None of the mentioned
Answer: C
The gain of the narrow band-pass filter must satisfy the condition,
AF= 2×Q2
When Q=3,
=> 2×Q2 =2×(32) =18.
=> 10<18.
Hence the condition is satisfied when Q=3.
24. The advantage of a narrow band-pass filter is
A. fc can be changed without changing gain
B. fc can be changed without changing bandwidth
C. fc can be changed without changing resistors
D. All of the mentioned
Answer: D
The narrow band-pass filter has multiple filters. The center frequency can be changed to a new frequency without changing the gain or bandwidth and is accomplished by changing the resistor to a new value which is given as
R’=R×(fL/fc)2.
25. How many types of band elimination filters are present
A. Three
B. Two
C. Four
D. None of the mentioned
Answer: B
Band-reject filters are also called as band elimination filters. They are classified into two types.
i) Wide band-reject filter and
ii) Narrow band-reject filter.
