Help me understand Bridged-T RC Filters

[Rob Strand]

The capacitor ratio determines the depth of the notch.
In this circuit the Q (which defines the bandwidth of the notch) and the notch depth are related.  You can't change one without changing the other.

[garybdmd]

Hi there,
I've spent several days trying to figure out this bridged T circuit and the basic
formulas someone would need.  I made/derived a formula for Q and bandwidth
which are estimates only, but quick and easy.  Here is a summary of everything
I found.  The Q formula and bandwidth formulas I came up with and if you'd like
to see how I did it you can check out what I did.

https://sites.google.com/site/garydavenportelectronics/home/bridgedtnotchfilter


     -------C1-----
     |            |
in --|            |--- out
     |            |
     --R1------R2--
          |
          C2
          |
         ///

                        1
center frequency = ------------------
                   2pisqrt(R1R2C1C2)

                   1 + R2/R1
notch depth= --------------------
               1 + R2/R1 + C2/C1

                        1          1   
bandwidth estimate = -------  -  -------
                    2piR2C1      2piR1C2

                 sqrt(c2/c1)
Q estimate =   -------------
                (c2/c1)-1

db loss at center freq = 10 log (notch depth)

I would appreciate any critiques/suggestions about this because its quite complicated.