Have try autocad, seem no problem when exported to any of CAM software
When you open the SC exported dxf file in AUTOCAD, the circles come as circles and no issue is faced. Whereas when imported into CAM software, it is getting imported as a spline. Did I understand correctly? If this is correct, I think this is an issue with the CAM software translation, and I would suggest getting in touch with their support. I will still confirm this with the experts and will let you know.
i have try changing the rendering quality to high ---then the circle will definitely look smooth
After you have increased the rendering quality, did the CAM software import, imported as a circle? Can you change the Display>graphics>wireframe and try again and see if that helps?