A 2.5-GHz direct digital frequency synthesizer with spurious noise cancellation

A 2.5GHz Direct Digital Frequency Synthesizer (DDS) with spurious noise cancellation is presented. Seven auxiliary DDSs have been used as spur cancellers which can generate opposition signal to counteract the spurs in DDS's output spectrum. Principle of spur cancellation and its implementation scheme is discussed. Key steps of spur cancellation procedure are also described. This DDS is implemented in a 0.18μm CMOS technology, occupies 4.6mm × 4.2mm including bond pads. Measured performance is SFDR > 58 dB for output signal frequencies up to 1 GHz, more than 20 dB's improvement is achieved comparing to its intrinsic SFDR performance.