Simple Single Op Amp Band Pass Filter

This is a circuit design for a band pass filter. A band pass filter passes a range of frequencies while rejecting frequencies outside the upper and lower limits of the pass band. The range of frequencies to be passed is called the pass band and extends from a point below the center frequency to a point above the center frequency where the output voltage falls about 70% of the output voltage at the center frequency. This is the figure of the circuit.


The filter bandwidth (BW) is the difference between the upper and lower pass band frequencies. The quality factors, or Q of the filter is a measure of the distance between the upper and lower frequency points and is defined as (Center Frequency / BW) so that as the pass band gets narrower around the same center frequency, the Q factor becomes higher. For a single op-amp band pass filter with both capacitors the same value, the Q factor must be greater than the square root of half the gain, so that a gain of 98 would require a Q factor of 7 or more.