Looking at what I just wrote, the cutoff frequency of the filter may only be at 3dB, with 6dB/octave dropoff after that, so I may not be exactly right in the details, but this should get you pretty close to what you want. Off the top of my head, if you wanted 6dB at the cutoff frequency (instead of 3dB) you could put two first-order filters in series with the same cutoff frequency of 200Hz.
