The easiest way is probably using a digital circuit with output rise time in the range you want (i.e. 200ps or less). The choice of digital circuits would be pretty wide, e.g. logic gates, comparators, clock buffers, limiting amplifiers and more. CML outputs would be preferable for easy 50 ohm output matching
I personally had great success with limiting amplifiers like ONET8501P - they have differential inputs with high sensitivity and 50 ohm CML outputs with fast rise times and little or no ringing