07-03-2011, 02:55 PM
Submitted by
SURENDRA JALU
[attachment=9701]
WIDE RANGE BAND PASS FILTER
DESCRIPTION:
Third-Order Wideband Bandpass Filter
This circuit demonstrates the operation and characteristics of a wideband bandpass filter, constructed by cascading a second-order low-pass and a high-pass filter. As a result, a 300 Hz to 3 kHz bandpass voice filter is formed.
Experiments:
Set the function generator to 1 kHz and the oscilloscope's time base to 0.2 ms/DIV. Increase the input frequency, about 1 kHz at a time up to 4 kHz, constantly observing the peak output voltage. How do these frequency changes affect the output voltage? Is it attenuated? What is the filter's gain at fin = 3 kHz? Is it close to 0.7? It if is, what is the frequency called? It is the higher cutoff frequency.
Perform the same observation with the input frequency being decreased, about 100 Hz at a time down to about 250 Hz, adjusting the oscilloscope's time base accordingly. Adjust the input frequency until the filter's gain reaches about 0.7. What is the frequency called? It is the lower cutoff frequency.
Now, you are ready to calculate the filter's bandwidth. What would you call the frequency of 1 kHz?It is a resonant frequency. What occurs at that frequency? The filter's gain has its maximum at resonant frequency. What is the equality factor (Q) for wideband filters? Q equal 0.5.
