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Experiment 08
- To design RC low pass & high pass filter circuit with cutoff frequency of 5KHZ, also draw a frequency response: (a) magnitude response (b) phase response.
- To design RL low pass & high pass filter circuit with cutoff frequency of 5KHZ, also draw a frequency response: (a) magnitude response (b) phase response.
Introduction:
This laboratory studies the use of passive components to create filters to separate portions of time-dependent waveform. Filters are an essential tool in our complex world of mixed signals — both electronic and otherwise. Passive components (resistors, capacitors, and inductors) have long served as filter components for everything from selecting radio stations to filtering out electrical noise.
OBJECTIVES : (1) Calculate and measure cutoff frequency for series RC and RL filters. (2) Design simple RC low-pass & high pass filter. (3) Design simple RL low-pass & high pass filter. (4) Bode plots for series filters.
LAB DISCUSSIONS:
Frequency Response The frequency response of a circuit is the variation in its behavior with change in signal frequency. Transfer Function The transfer function of a circuit is the frequency dependent ratio of a phasor output y () (an element voltage or current) to a phasor input X () (source voltage or current). Bode Plots Bode plots are semi-log plots of the magnitude (in decibels) and phase (in degrees) of a transfer function versus frequency.
Cutoff Frequency The frequency at which gain becomes 0.707 times of the maximum gain is called cutoff frequency. It is also called the half power frequency because at this frequency the average power delivered by the circuit is one half the maximum average power.
Filter A filter is a circuit that is designed to pass signals with desired frequencies and reject or attenuate others.
Passive Filters Elements used in passive filters are resistors, capacitors and inductors. The gain of passive filters is unity. Low Pass Filter A low pass filter passes low frequencies and rejects high frequencies.
Magnitude Bode Plot for First-Order Low Pass Filter
Phase Bode Plot for First-Order Low Pass Filter
Phase Bode Plot for First-Order High Pass Filter
TASK 1: RC Low Pass Filter:
Set up the circuit. Use the function generator FGEN for the supply voltage vin 10 VP-P.
Connect channels 1 and 2 of the oscilloscope to measure V s and V out simultaneously.
Vary the frequency from 500 Hz to 10 kHz in steps , and record the indicated value. With each frequency change, make sure that V in is still 10V pp.
For RC Circuit C=2.2nF R=15kohm Frequency=60-60KHz
For RL Circuit L=1mH R=38Ohms Frequency=60-60KHz
RC Low Pass Filter Circuit
Calculated Results:
Frequency (KHz)
0.01fc=50 1.
*10^
0.1fC =500 1.
*10^
0.5fc =2.
K
9*10^5 1.475 -1.9 -
fc = 5K 1.8*10^6 1.96 -2.1 -27.
2fc = 10 K 3.6*10^6 2.34 -2.34 -36.
4fc = 20 K 7.2*10^6 2.55 -2.53 -45.
6fc =30 K 1.08*10^
7
8fc = 40 K 1.4*10^7 2.9 -3.12 -63.
10fc =50 K 1.8*^7 3.2 -3.6 -72.
100fc =
500K
1.8*10^8 3.5 -4.12 -86.
Task 1: Passive RC Low Pass Filter
Frequency (KHz) (^) Vp-p(input) Vout
0.01fc=10Hz 10v 840mv 0.1fC =100Hz 10v 890mv
0.5fc =500Hz 10v 990mv
fc =1K 10v 1.002v 2fc =2K 10v 2.02v
4fc =4K 10v 2.03v 6fc =6K 10v 3.50v
8fc =8K 10v 4v
4fc = 20 K 7.2*10^ 6
6fc =30 K 1.08* ^
8fc = 40 K 1.4*10^ 7
10fc =50 K 1.8*^7 3.2 -3.6 72.
100fc = 500K
1.8*10^
Frequency (KHz) (^) Vp-p(input) Vout
0.01fc=10Hz 10v 136mv 0.1fC =100Hz 10v 150mv
0.5fc =500Hz 10v 1.021v fc =1K 10v 2.001v
2fc =2K 10v 3.05v
4fc =4K 10v 4.03v 6fc =6K 10v 5.002v
8fc =8K 10v 5.40v
10fc =10K 10v 6.20v 100fc =100K 10v 6.89v
Table 2 (RC High Pass Filter)
LTSPICE SIMULATION
Task 3: RL Low Pass Filter:
Calculated Results:
Frequency (KHz)
0.01fc=50 1. *10^
0.1fC =500 1. *10^
0.5fc =2. K
9*10^5 1.475 -1.9 -
fc = 5K 1.8*10^ 6
2fc = 10 K 3.6*10^ 6
4fc = 20 K 7.2*10^ 6
6fc =30 K 1.08* ^
8fc = 40 K 1.4*10^ 7
10fc =50 K 1.8*^7 3.2 -3.6 -74.
100fc = 500K
1.8*10^
Frequency (KHz) Vp-p Vout 0.01fc=10Hz 10v 5v 0.1fC =100Hz 10v 5.87v 0.5fc =500hz 10v 6.50v
0.5fc =2.5 K 9*10^5 1.475 -1.9 18
fc = 5K 1.8*10^ 6
2fc = 10 K 3.6*10^ 6
4fc = 20 K 7.2*10^ 6
6fc =30 K 1.08* ^
8fc = 40 K 1.4*10^ 7
10fc =50 K 1.8*^7 3.2 -3.6 72.
100fc = 500K
1.8*10^
Frequency (KHz) (^) Vp-p(input) Vout 0.01fc=10Hz 10v 554mv 0.1fC =100Hz 10v 561mv 0.5fc =500Hz 10v 582mv fc =1K 10v 603mv 2fc =2K 10v 1.388v 4fc =4K 10v 2.01v 6fc =6K 10v 3.01v 8fc =8K 10v 3.02v 10fc =10K 10v 3.08v 100fc =100K 10v 5.002v
Table 4 (RL High Pass Filter) LTSPICE SIMULATION:
LOW PASS FILTER
HIGH PASS FILTER
PASSIVE LOW PASS FILTER
PASSIVE HIGH PASS FILTER
Conclusion:
We have learnt about High Pass and Low Pass Filters and
implemented it practically.
15KOhm
2.2nF
1mH
38Ohm
