Linear Integrated Circuit Multiple Choice Questions on “Band-Reject and All-Pass Filters”.
1. How many types of band elimination filters are present
A. Three
B. Two
C. Four
D. None of the mentioned
Answer: B
Clarification: 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.
2. Find the wide band-reject filter
Answer: B
Clarification: A wide band-reject filter is made using a low pass filter, a high pass filter and a summing amplifier.
3. A narrow band-reject filter is commonly called as
A. Notch filter
B. Band step filter
C. Delay filter
D. All of the mentioned
Answer: A
Clarification: A narrow band-reject filter is also called as notch filter because of its higher quality factor, Q (>10).
4. Find the expression for notch-out frequency?
A. fN = 2πRC
B. fN = 2π/RC
C. fN = 1/2π×√(R/C.
D. fN = 1/2πRC
Answer: D
Clarification: The notch-out frequency is the frequency at which maximum attenuation occurs: it is given by fN =1/2πRC.
5. The quality factor of passive twin T-network is increased by using
A. Inverting amplifier
B. Non-inverting amplifier
C. Voltage follower
D. Differential amplifier
Answer: C
Clarification: The passive twin T-network has a selectively low figure of merit. The Q of the network can be increased significantly, if it is used with the voltage follower.
6. Find out the application in which narrow band-reject filter can be used?
A. Embedded system
B. Biomedical instrument
C. Digital computer
D. None of the mentioned
Answer: B
Clarification: Notch filters or narrow band-reject filters are used in biomedical instruments for eliminating undesired frequencies.
7. Design 120Hzactive notch filter?
Answer: A
Clarification: Since C value n = 1/2πRC.
R= 1/(2πfnC.= 1/(2π×120Hz×0.68×10-6) = 1.95kΩ ≅2kΩ.
For R/2, parallel of two 2kΩ resistor
=>R/2 = 2kΩ||2kΩ =(2×2)/(2+2)=1kΩ.
For C/2 , parallel of two 0.68µF capacitor
C/2=> 0.68µF + 0.68µF= 1.36µF.
8. Find the application of area where all-pass filters are used?
A. Cathode ray oscilloscope
B. Television
C. Telephone wire
D. None of the mentioned
Answer: C
Clarification: When signals are transmitted in transmission lines like telephone wire, they undergo change in phase, all-pass filters are used to compensate these phase changes.
9. Determine the output voltage for all the all-pass filter and express it in complex form?
A. VO =Vin/ [(1-j2πfRC. /(1+ j2πfRC.].
B. VO =Vin× [(1+j2πfRC. /(1- j2πfRC.].
C. VO =Vin ×[(1- j2πfRC. /(1+ j2πfRC.].
D. None of the mentioned
Answer: C
Clarification: The output voltage of all-pass filter is given as VO =Vin× [(1-j2πfRC. /(1+j2πfRC.] .
10. Determine the input frequency for all-pass filter with phase angle as 62o. Consider the value of resistor and capacitor are 3.3kΩ and 4.7µF.
A. Input frequency= -7.65Hz
B. Input frequency= -6.77Hz
C. Input frequency= -3.89Hz
D. Input frequency= -9.65Hz
Answer: D
Clarification: The phase angle is given as Φ = -2tan-1×(2πfRC.
=> f=-tanΦ/4πRC =-tan(62o)/(4π×3.3kΩ×4.7µF)= -1.88/0.1948 =-9.65Hz.
11. Determine the angle for given circuit diagram, if the frequency of input signal is 1khz
A. -45o
B. -180o
C. -270o
D. -90o
Answer: D
Clarification: Phase angle Φ=-2tan-1×(2πfRC/1) = -2tan-1×(2π×1kHz×16kΩ×0.01µF)
= -2tan-1×(1.0048)=-90o.
12. The voltage gain magnitude of all-pass filter is
A. Zero
B. One
C. Infinity
D. None of the mentioned
Answer: B
Clarification: The magnitude of voltage gain of all-pass filter |VO /Vin| = √(1+(2π/RC.2) / √(1+(2 π/RC.2) =1.
13. What happens if the position of R and C are interchanged in the below circuit diagram?
A. Vin leads VO
B. Vin lags VO
C. VO leads Vin
D. VO leads Vin
Answer: C
Clarification: For the circuit given, the phase angle changes from 0 to 180o as frequency is varied from 0 to ∞. If the positions of R and C are interchanged, the phase shift and band width input and output becomes positive. That is the output (VO) leads input (Vin).
14. Choose the incorrect statement “In wide band-reject filter” .
A. Low cut-off frequency of low pass filter must be larger than the high cut-off frequency of the high pass filter.
B. Low cut-off frequency of high pass filter must be equal than the high cut-off frequency of the high pass filter.
C. Low cut-off frequency of high pass filter must be smaller than the high cut-off frequency of the low pass filter.
D. None of the mentioned
Answer: D
Clarification: In wide band-reject filter, low cut-off frequency of high pass filter must be larger than the high cut-off frequency of the low pass filter.