Your question is a little ambiguous.
If you reffer to the fact that a square signal is an infinite sum of sine signals, then decomp your square signal in Fourier Series and pick the fundamental and maybe 1st harmonic.
Based on comparator,I can get a full square-wave with a full sine wave.It is easy with a chip named MAX998. I want to get more square waves.for example,30,50 etc.Do you have an idea? thanks!
From the 2 square waves generated from the sin & cos sine waves you can generate 4 different square waves by appropriate logic combinations. If you need more, first frequency-multiply the 2 square waves by 2, 4, 8, ..., then generate the required phase shifted square waves again by appropriate logic combinations. Or start from a corresponding higher frequency, then divide by 2, 4, 8, ..., and use appropriate logic combinations.