I made a rough sinewave with 10 digital steps added together. The steps caused pretty bad high frequency multiple harmonics which I filtered out with two 4th-order LMF40 switched-capacitor Butterworth lowpass filters in series. The filters had a small amount of clock frequency which I filtered out with a 2nd-order Sallen-Key lowpass filter made from an opamp.
Here is a digital stepped sinewave with 20 steps (mine has 10 steps):
Here is a digital stepped sinewave with 20 steps (mine has 10 steps):