Operational Amplifier Applications Unit 5 – Band Pass Filter
Exercise 1 – Band Pass Filter Frequency Response
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to determine the frequency response
characteristics of an active bandpass filter by analyzing input and output signals. You will verify
your results with an oscilloscope.
DISCUSSION
- The center frequency is at the midpoint of the passband.
- The lower cutoff frequency is the point below the center frequency at which the output is 3
dB below the maximum gain. - The upper cutoff frequency is the point above the center frequency at which the output is 3
dB below the maximum gain. - The passband is the frequency range between the lower cutoff frequency and the upper cutoff
frequency. - The bandwidth of the passband is determined using this equation: BW = f 2 − f 1
- Bandpass filters are classified as narrow-band or wide-band. If the bandwidth is less than or
equal to 10% of the center frequency, the filter is a narrow-band type. If the bandwidth is
greater than 10% of the center frequency, the filter is a wide-band type. - Bandpass filters select a narrow range of frequencies from a relatively wide frequency
spectrum. This selectivity is expressed by the bandpass filter’s quality factor, or Q-factor. - The Q-factor is defined by the equation: Q = f 0 /BW
- A high-Q filter has a minimum Q of 10. Low-Q filters have a Q of below 10.