Lee Wei Yan
Avago Technologies

Absolute encoders using optical technology often face limitations in resolution and size. For example, to achieve a higher resolution of up to 16-bits, the absolute encoder has to be combined with an incremental pattern that is strongly interpolated with an external hardware and signal conditioning circuits. Alternatively, design engineers may use high-speed digital signal processors (DSPs) to implement signal processing algorithms and calibration coefficients that can be stored in non-volatile memory. The latter method enables the development of a fully integrated solution that is small in size, coupled with an increase in accuracy and resolution, which is not possible with conventional encoders. However, the software overhead means limited read-out rate is available. These types of encoders are only suitable for low-speed feedback control applications that require high accuracy.

In this paper, we present the DSP design approach, and the hardware and software implementation of a quasi-absolute encoder solution.