How to amplify a 25khz square wave that goes from -3.3v to +3.3v so that the amplitude is doubled
You can run a 25KHz square wave through a 2:1 step-up transformer using a non-gapped core with little distortion if you are careful that the square wave has a duty cycle of exactly 50% and, if you use a push-pull winding on the primary, wind bifilar so that you have exactly the same number of turns.  Any lack of symmetry will result in the having a DC bias and the output will be distorted.  I often run a "D" flip flop divide-by-two on the driver circuit to make sure the waveform stays at 50%.