third order butterworth

[klund at MIT.EDU]

Circuit of the day:  third order butterworth filter using only two
capacitor values, 1% resistors, and an opamp connected as a unity gain
follower.  Cutoff frequency = 1/(2piRC).

                           C  
                       +----||-------------+ 
                       |            |\     |
      1.292R    2.094R |  3.698R    |  \   |
V_I --/\/\/--+--/\/\/--+--/\/\/--+--| 1 >--+-- V_O
             |                   |  |  /    
          C ===            0.1C === |/
             |                   |
             V                   V

--> Kent.