High speed high resolution direct digital frequency synthesizer with non-linear DAC coarse quantization and ROM-based piecewise linear interpolation

Abstract

A high speed high resolution direct digital frequency synthesizer (DDFS) architecture is presented. The proposed architecture combines the advantage of ROM-based DDFS and nonlinear DAC (NLDAC) based DDFS. The phase-to-amplitude mapping is implemented with NLDAC coarse quantization and further increase its resolution by adding a ROM-based piecewise linear interpolation. ROM size is reduced by using coarse-fine decomposition. A ROM compression ratio of 32 is achieved by further combing the adjacent lines in the same segment into one straight line. A 4-GHz 32-bit DDFS is implemented based on the proposed architecture. The prototype DDFS is fabricated in 0.25 μm SiGe HBT process. The DDFS with 9-bit amplitude resolution are capable of producing a minimum spurious-free dynamic range (SFDR) of 46 dBc up to Nyquist frequency at the clock frequency of 4.0 GHz. Compared with state-of-the-art DDFSs the proposed DDFS demonstrates excellent performance.