How does a designer create the best Low Q Band Pass Filter?

Problem:
How does a designer create the best Low Q Band Pass Filter?

Solution:
The best low Q bandpass filter may not be a bandpass filter at all. It may be a high pass filter cascaded with a low pass filter:



The reader is urged to click on the graphic to enlarge it and see the details better. Some points are worth noting:

• The figure shows the effect of cascading double pole Butterworth filters.
  
  
• Both the high pass and low pass filters must have the same gain.
  
  
• The high pass stage must come first, followed by the low pass. In this way, high frequency noise from the high pass filter will be attenuated by the low pass filter.
  
  
• Cascaded high pass and low pass filters probably take the same number of opamps as cascading bandpass filters. Yet the response is clearly sharper, giving a double pole characteristic at the low and high frequency 3 dB points, instead of 6 dB of roll off caused by cascading two bandpass filters with single pole response.