A Quarter-ROM DDS Using Phase Accumulator with Subtraction

摘要

The conventional ROM-based direct digital frequency synthesizers (DDS) cannot output the high speed frequency due to a longer access time of the ROM table, therefore, a quarter wave symmetry technique that stores only one quarter of a sine wave is used to reduce the ROM table size. However, the sine wave produced by the DDS will have a poor symmetry if directly using the output of the phase accumulator to access a quarter ROM. In this paper, a phase accumulator with subtraction operation is proposed to improve the symmetry of the conventional quarter-ROM DDS, and this design does not require much hardware complexity.