I have a DDS chip with complementary current outputs that I need to filter. I'm using a design like this:
I need a different cutoff frequency, however - 2MHz instead of 50KHz. Note that I'm not using the particular opamps specified in that schematic - I'm using the LT6207 instead.
I understand the basic operation - TIAs followed by a differential input amplifier - and after reading the active filter design techniques chapter for Opamps for Everyone, I think I understand the basics of active filters, but I'm stumped as to how to apply those principles to this design.
Unless I'm mistaken, it consists of a first order filter (the TIAs) followed by a third order filter, which violates Opamps for Everyone's prescription that only odd order filters contain order-1 stages. Thus, their calculations and coefficient tables don't seem to be terribly useful.
How can I calculate the component values to adjust my filter for a new cutoff frequency?