The encoder we had was on a little PCB that you get when you buy one of those Chinese Arduino 37 sensor kits. (By the way, if you are looking for documentation on those kinds of boards, look here ...

Two opamps on two coils produce a quadrature signal just like a normal encoder. When the shaft turns in one direction, one pulse will lead the other.

Makers, developers and Arduino enthusiasts searching for silent stepper drivers with high resolution encoders which are also Arduino compatible.