17. Multimode Transmitters with ΔΣ-Based All-Digital RF Signal Generation

This paper presents an all-digital approach to the generation of the modulated radio-frequency carrier and its application to a multimode transmitter in today’s communication systems and draws a possible picture of tomorrow’s systems. We will first analyze how digital transmitters will progressively replace their analog counterparts and what are the main issues associated with this trend. The combination of Δ​Σ modulation and digital mixing is proposed as an innovative approach enabling multimode operation of transmitters with low power consumption and chip area, easy configurability, and good performance. A 90 nm CMOS chip has been designed to demonstrate the feasibility of the concept and its potential in multimode transmitter architectures. Techniques such as redundant arithmetic and non-exact quantization are used in the high-speed Δ​Σ modulator implementation. Furthermore, approaches to antenna filtering using BAW filters and reconfigurable semi-digital RF FIR filters will be introduced. Finally, a review of recent outstanding transmitter designs will allow a comparison between the presented approach and architectures based on digital-to-RF conversion.