Abstract: An encoder apparatus to measure a position of an object from an input analogue signal includes a driving plate which varies according to the position of the object, an optical device to receive a light response from the driving plate and to output a sinusoidal wave analogue signal according to an amount of the driving plate's movement, an analogue to digital (A/D) converter to output a normalized sinusoidal wave digital signal converted from the analogue signal outputted from the optical device, and a calibration unit to convert the sinusoidal wave digital signal outputted from the A/D converter into a triangular wave signal.