level shifting - How do you shift a square wave down?

I have a square wave the oscilates at 25khz from 0 to 30v. I would like it to oscillate from -15v to +15v. Is there a SUPER DUPER SIMPLE circuit to do this? Keep in mind it's going up and down at 25khz.

Here's the circuit. The square wave I want to shift is going into the PiezoSpeaker at the lower right of the circuit.

Answer

How do you shift a square wave down?

Just an RC will do it: -

If fed with a sine wave (for the convenience of the attached picture), it will reproduce the sine wave at the output but with the DC level removed thus maintaining the correct peak-to-peak amplitude. Here is what happens in the first few cycles as the DC level is removed: -

It will work in the same way as a square wave (DC or average value = 15 V will be removed) but, please ensure that 2\$\pi\$RC << than 40 us to ensure the following doesn't happen: -

If C = 10 uF and R = 1 kohm, the cut-off frequency will be 15.9 hertz and miles away from causing the droop problem seen above.

However, if you in fact have a non 50:50 duty cycle square wave you may need a more complex circuit because the DC level won't be at the midpoint of the waveform.

On the other hand, if you are driving a simple piezo transducer, why bother shifting it to equal positive and negative levels - it's purely capacitive and it won't care so, a really simple circuit becomes "a wire".