The AD639 is a general trigonometric function generator where the output is a scaled ratio of two sines, pill where each sine has tunable parameters. The package on this one was another ceramic case with a gold cover that was held on by solder. Heating the case and pushing over the solder revealed a very clean chip with a seemingly small number of transistors. No markings were found on the chip other than the model number and Analog’s logo.
( ad639.pdf )