Second Order Active Low Pass And High Pass Filters
Experiment 9
Aim:
To construct and study the frequency response of Second Order Low Pass Filter and High Pass Filter.
Apparatus required:
Theory:
An improved filter response can be obtained by a second order active filter. A second order filter consists of two RC pairs and has a roll-off rate of -40 db/decade. A general second order filter (Sallen-key filter) is shown. The results derived here can be used for analyzing low pass and high pass filters. LOW PASS FILTER:Low pass filter which passes signals below the cut off frequency. At low frequency both capacitors are opened and circuit becomes voltage follower. Second order responses 3 db down at cut off frequency.HIGH PASS FILTER:High pass filter is a filter which passes signals above the cut off frequency. At low frequency capacitors are opened and voltage gain is zero. At high frequencies capacitors appears shorted and the circuit becomes voltage follower. Second order responses 3 db down at cut off frequency.
Circuit Diagram:
Procedure:
Connections are made as per the circuit diagram.
Design values are set as per the design
Voltages are noted for different frequencies
Gain is calculated with Gain = 20 log V0/Vin
Graph is drawn between frequency and Gain.
Tabulation:
Result:
The frequency response of Second order Low Pass Filter and High Pass Filter was studied and the graph is plotted.
Link to experiment
Go here and select Experiment 9
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