Single-chip velocity measurement system for incremental optical encoders

A single-chip system is designed, implemented, tested, and analyzed for the measurement of velocity from incremental optical encoders with quadrature outputs. The system uses a field programmable gate array (FPGA) chip to take advantage of high flexibility and a low-cost design cycle. The device uses two counting methods: period counting for low velocities and frequency counting for high velocities to obtain high resolution measurements for a wide range of velocities with a fixed 16-b word length. Verification testing of the device was consistent with predicted error and showed that quantization errors can be made arbitrarily small by adjusting the tradeoff between velocity range and minimum resolution. This tradeoff can be adjusted by the designer by simple modifications to the basic design.