Betul, You are on the right track. Couple of things - you really need a 3rd-order filter to get close to a sine-wave. The db/decade roll off of a 1st order filter is very slow and allows the higher-order harmonics to come through. This page has good online calculator: http://sim.okawa-denshi.jp/en/Fkeisan.htm Also be careful about the values you choose when it comes to impedance matching. I don't know what the sine wave is feeding, but your filter is high-impedance (47K). See this attached simulation of 3rd-order RC filter with 15K resistors (impedance is ~45K). I roughly modeled the MSP430 output with 20 ohms and 10pF and normalized it to 1V.
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