The AD639 is a trigonometric function converter chip that was made by Analog Devices, and is now obsolete. They, however, do not make a replacement. http://www.analog.com/UploadedFiles/Obsolete_Data_Sheets/55889558331308887AD639.pdf 1. Does anyone else make a similar chip ? 2. Do you know any reliable distributors for obsolete electronics that I can call for the AD639 ? 3. If nothing comes out of 1 and 2, what's the next best way to generate a low-distortion sinewave, from a triangle-wave input ? Any help is appreciated.