Digital polyphase baseband for direct digital generation of high sample rate radio frequency signals

In this paper the concept, application and implementation of digital polyphase baseband is presented. This concept simplifies direct control of highly efficient switching-mode power amplifiers with sample rates above the carrier frequency of multiple gigahertz. Flexible digital transmitter architectures for wireless applications like direct pulse width/position modulation or ΔΣ modulation transmitters become feasible with this concept. In the proposed approach the baseband is represented by multiple digital subsignals. The parallel nature of the subsignals allows individual, less time critical, calculation. These subsignals are serialized and, thus, up-converted to the carrier frequency and used to directly drive the PA. Because the signal is converted to the analogue domain only after the PA by passive filtering, this transmitter architecture is not sensitive to nonlineartrities of the building block. Using the digital polyphase baseband allows direct digital generation of radio frequency (RF) signals with carrier frequencies, f_c, above 1GHz.