There are lots of different types of chopper circuit, but in general they produce a square-wave or near-square wave output. You can convert this to a sine wave by using a low pass filter.
If you are using a high frequency chopper (e.g. stepper driver, class d; audio amp/etc) the same thing applies, except that the load will have a significant effect on the behavior of the filter (and may act as a filter itself).
If you post more details I can give you a more specific answer.
