30-06-2012, 02:23 PM
To plot the frequency response of m-derived low pass filter.
To plot the frequency response of m-derived low pass filter..docx (Size: 26.72 KB / Downloads: 49)
THEORY:
There are two disadvantages of constant k filters:
1. The attenuation does not increase rapidly beyond cut-ff frequencies.
2. Characteristic impedance varies widely in the pass band from the desired value.
In order to overcome these disadvantages of constant k filters a special type of filter called m-derived filter has been implemented. In m-derived filter, it is possible to design a filter to have the same impedance throughout the pass band and stop band like constant k filter but with a different degree of attenuation outside the pass band. In the m-derived filter, it becomes possible to get very rapid attenuation rise in the stop band and just beyond the cut-ff frequency. However, it fails to provide constant characteristic impedance over the entire pass band.
A m-derived T and Π sections of the passive filter are shown below, where, 0<m<1:
A low pass filter is one, which passes low frequencies up to cut-off frequency and attenuates the rest of frequencies.
For the m-derived sections, at a particular frequency the shunt arm of T-section or series arm of Π-section will be in resonance giving a short circuit to the input for T section and open circuit for Π-section causing infinite attenuation. This particular frequency is denoted by f∞.
PROCEDURE:
1. Connect sine wave generator at the input of the filter. Adjust sine wave amplitude to 5Volt p-p. Keep the input voltage constant throughout the experiment.
2. Connect CRO at the output of the filter.
3. Vary the input frequency from minimum to 10KHz in proper steps in sine wave generator and every time note the input frequency and corresponding output voltage from the CRO in the observation table.
4. Plot the graph between input frequency & Output Voltage taking input frequency (in Hz) on x-axis and output voltage (in Volts) on y- axis on semi log graph paper.
5. Calculate the cut-off frequencies from the formula as well as from the graph.