A 10GHz nonlinear cosine-weighted digital-to-analog converter for high-speed direct digital synthesis

A SiGe cosine-weighted digital-to-analog converter (DAC) with 10 GHz sampling rate is presented. The nonlinear DAC is used in a direct digital synthesis (DDS) to replace the conventional look up table and the linear DAC. It takes the advantage of high switching speed of SiGe current switches and uses the current mode logic (CML) circuits to realize the digital control logic. The DAC is designed using a 47 GHz SiGe technology and achieves a maximum 5 GHz output frequency with 10 GHz clock.