There are Synchro converters or transducers used on aircraft to measure angle of attack using 3 sinusoidal inputs. I could not understand where these 3 inputs come from and what angle information is generated by the synchro converter on the basis of the input signals?
The angle of attack sensor turns the shaft on a synchro (or a resolver: they're essentially the same thing) which is a transformer whose outputs are uniquely related to that shaft angle. That's where your 3 inputs come from. There are lots of possibilities for what happens next. The shaft angle is not the same as the angle of attack. The synchro is not measuring. It's just conveying measurement information from the sensor to the flight crew and other aircraft systems.