Digital transmitter design for mobile devices

The advancement of the process technology, especially CMOS technology, has played a major role in the miniaturization of the mobile device as well as extending its battery life. As digital logic continues to shrink in size and increase in density, implementing RF/analog functions digitally becomes increasingly more attractive. RF/analog digitization not only allows the design blocks to benefit from process scaling, but also enables a more complete system-on-chip integration. In this article, several digitally enhanced CMOS transmitter implementations are discussed, and their trade-offs are analyzed. A digital quadrature transmitter that is process-scaling-friendly and multimode-capable is presented at the end. The chip is implemented in 40 nm CMOS process and can easily be integrated with digital baseband processors.