Toward Millimeter-Wave DACs: Challenges and Opportunities

As line widths in emerging III-V technologies approaching that of modern CMOS, the conception of high performance mixed signal designs such as digital to analog converters (DACs) in the mm-wave space becomes possible. While addressing the speed limitations, candidate III-Vs (InP, GaAs and GaN) are known to suffer from increased switching power consumption, limited device yield and absolute accuracy. CMOS, on the other hand, has the benefit of low-power digital switching, fine resolution and scalability. Recent attempts in marrying the two technologies have been carried out in the DARPA COSMOS program, by integrating III-V type devices with CMOS circuits, so as to exploit the advantages of low-power digital CMOS and high-speed high-power InP. This paper presents some of the challenges as well as prospects in designing record speed and performance DACs in the COSMOS program while contrasting it to that of deeply-scaled CMOS. A multi-phase parallel DAC architecture is leveraged for ultra-wideband synthesis, to improve noise performance and achieve higher information rates. The architectural bounds between CMOS and InP as well as detailed circuit-level analysis of critical block elements will be highlighted.