[Cruisin Marine]

Why is a sinewave required, and for what purpose- what will it be driving?

That may help in deciding the cct. design.

A simple NPN emitter follower with a simple pi LPF on the o/p side should suffice for most purposes.

You can (and often is preferable) have different in and out impedance's on the LPF, you can easily have a say 300- 1000 ohm on the emitter and transform that down to be 50 on the output socket or whatever.

Almost any old TTL or CMOS will be fine to drive the emitter follower with appropriate interfacing/matching to turn the the base of the NPN device on and off (>0.6v), if required, the simple potential divider for the base bias should be enough, or even just a base to earth resistor may suffice (I would use about 560 ohm) perhaps with a series resistor from the square wave drive (if needed) all capacitively coupled in with a say 1-10nF or so.