Study of frequency response of active filters HP, LP & BP.
Power Supply, Filter circuit. Kit, Resistances, Audio Frequency Generator, two voltmeters.
High Pass FilterA HP filter attenuates all frequencies below a designated cut-off frequency fc , & passes all freq. above fc. Thus the pass band of this filter is the freq. range above f_{c}& the stop band is the freq. range below f_{c}. An attenuation characteristic of a HP filter is shown in fig.
S. No | Frequency (KHz) | I/P Voltage V_{1}(Volts) | O/P Voltage V_{2}(Volts) | α = 20 log V _{2} /V _{1} |
1 | ||||
2 | ||||
3 | ||||
4 | ||||
5 |
α = 20 log V _{2} /V _{1}
Graph:
Low Pass Filter A Low pass filter is one which passes without attenuation all frequencies up to the cut-off frequency fc & simultaneously attenuates all other frequencies greater than fc. The attenuation characteristic of an ideal L P filter is shown in fig.
This filter transmits all frequencies from zero to cut-off frequency. The band is called pass band. The frequency range over which transmission does not take place is called the stop band.
fc = 1/ π(LC)½
Circuit Diagram
S. No | Frequency (KHz) | I/P Voltage V_{1}(Volts) | O/P Voltage V_{2}(Volts) | α = 20 log V _{2} /V _{1} |
1 | ||||
2 | ||||
3 | ||||
4 | ||||
5 |
α = 20 log V _{2} /V _{1}
Graph:
Band Pass Filter A band pass filter passes freq. Between two designated cut-0ff freq.& attenuates all other freq. . BPF has two cut-off freq. As shown in fig. f1 is called lower cut-off freq.& f2 is upper cut-off freq.
Circuit Diagram:
S. No | Frequency (KHz) | I/P Voltage V_{1}(Volts) | O/P Voltage V_{2}(Volts) | α = 20 log V _{2} /V _{1} |
1 | ||||
2 | ||||
3 | ||||
4 | ||||
5 |
α = 20 log V _{2} /V _{1}
Graph:
Result/ConclusionThe frequency response of High pass, Low pass and Band Pass Filter has been plotted on the graph.
Discussion:High Pass Filter passes the frequencies above cut-off frequencies. Low Pass Filter passes the frequencies below cut-off frequencies
The Band Pass Filter is obtained by connecting Low Pass and High Pass Filter in cascade provided that the Low Pass Filter has cut-off frequency higher than High Pass Filter.
Q1:Define Filter ?
A1:A filter is an electrical network that can transmit signals within a specified frequency range
Q2:Define Pass Band?
A2:The frequency range which is passed by the filter is called pass band
Q3:Define Stop Band?
A3:The frequency range which is suppressed by the filter is called stop band.
Q4:Define Cut-Off frequency?
A4:The frequency that separates the pass band & attenuation band is known as the cut-off frequency.
Q5: Define High Pass Filter?
A5:A high pass filter attenuates all frequency below the cut-off frequency & allows to pass all other frequencies above the cut-off frequency
Q6:A high pass filter is one which (a) passes all high freq. (b)attenuates all low freq. (c)attenuates all freq. below designated cut-off freq. & passes all freq. above cut-off
A6:(c)
Q7:Where filter circuits are used ?
A7:Filter circuits are used in TV receivers, audio amplifiers etc.
Q8:What are the units of attenuation?
A8:Decibles (dB) & Nepers.
Q9:An ideal filter should have (a) Zero attenuation in the pass band (b) Infinite attenuation in the pass band (c) Zero attenuation in the attenuation band
A9:(a)
Q10:In the m-derived high pass filter, the resonant frequency is to be chosen so that it is (a)Above the cut-off frequency (b)Below the cut-off frequency (c)None of the above
A10:(c)
Q11:. Define Low Pass Filter?
A11:The low pass filter allows all frequencies up to the specified cut-off frequency to pass through it & attenuates all the other frequencies above the cut-off frequencies.
Q12:Define cut-off frequency?
A12: It demarcates the pass band & the stop band
Q13:What is the freq. Range of Pass Band?
A13:The frequency range of pass band is from 0 to fc.
Q14:What is the freq. Range of Stop Band?
A14:The frequency range of stop band is from fc to ∞.
Q15:Relation between Decibel & Nepers?
A15:Attenuation in dB = 8.686 * attenuation in nepers
Q16:Neper-------*dB.
A16:0.115.
Q17:.In the m-derived low pass filter, the resonant frequency is to be chosen so that it is (a)Above the cut-off frequency (b)Below the cut- off frequency (c)None of the above
A17:(a)
Q18:Give the classification of filters depending upon the relation between Z1 & Z2
A18:Constant K- filters & m-derived filters.
Q19:Give the classification of filters on the basis of frequency
A19:Low pass , High pass , band pass & band elimination filters
Q20:Define decibel.
A20:It is defined as ten times the common logarithms of the ratio of input power to the output power.
Q21:Define Band Pass Filter?
A21:It is a combination of two parallel tuned circuits
Q22:Can a combination of Low Pass& High Pass Filters use as a Band Pass filter, how?
A22:Yes, By cascading LPF & HPF provided that the low pass filter has cut-off frequency higher
Q23:A Band Pass Filter is one which Passes all high freq. (b) Attenuates all low freq. (c) attenuates all freq. below a designated cut-off frequency & passes all above cut-off frequency
A23:(c)
Q24:The propagation constant of a symmetrical T-section & π-section are the same (a) true (b) false
A24:True.
Q25:What is Prototype Filter?
A25:Any filter where the relationship Z1Z2 = R02 is maintained is known as constant K or prototype filter.
Q26:Define Attenuators?
A26:An attenuator is a two-port resistive network & its propagation function is real
Q27:Write the expression of resonance frequency in terms of two cut-off frequencies?
A27:fo = (f1 f2)1/2.
Q28:Explain the making of High Pass Filter
A28:Capacitors in series arm & inductor in series arm
Q29:Define Neper
A29:It is defined as the natural logarithm of the ratio of input voltage (or current) to the output voltage (or current) provided that the network is terminated in its characteristic impedance Z0.
Q30:Is filter a resistive or reactive network
A30:Reactive network
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