A 4-GHz 32-bit direct digital frequency synthesizer in 0.25 µm SiGe HBT with SFDR > 46 dBc up to Nyquist bandwidth

Abstract

A 32-bit direct digital frequency synthesizer with a maximum operating frequency of 4.5 GHz fabricated in 0.25 μm SiGe HBT is presented. The phase-to-amplitude mapping circuit is implemented with nonlinear DAC coarse quantization and ROM-based piecewise linear interpolation. The measured SFDR is between 46 dBc and 60 dBc under a 4.0 GHz clock and the hopping time is less than 10 ns. This chip occupies 5.25 mm2 including bond pads and dissipates 3.46 W with a 4.0 V digital supply and 4.0V analog supply. The proposed DDFS demonstrates excellent performance achieving a FOM of 234.9 GHz · 2(SFDR/6)/W.