Radio transmitter architecture with all-digital modulator for opportunistic radio and modern wireless terminals

This paper presents a new concept of transmitter architecture based on a fully digital circuit featuring a radiofrequency modulator. The RF transmitter under study shall offer enough flexibility and reconfigurability to take up the challenges of "opportunistic radio" and the so-called opportunistic terminals must be able to transmit context dependent waveforms in licensed and unlicensed bands. This appears more achievable with an all-digital transmitter, possibly implemented in CMOS technology. This digital circuit will provide means for generating various modulations, over-sampling signals, shaping the noise, modulating low resolution signals onto the transmit channel, and converting it to analogue. It is also associated with very selective analogue BAW-CRFfilters that highly reject the noise outside the transmit band. The proposed arrangement successfully combines the advantages of programmability, avoidance of all analogue variables (temperature, component, frequency and process variations), high selectivity and flexibility.