Spezifikation und Charakterisierung eines volldigitalen Sendepfades für breitbandige und energieeffiziente Multistandard-RF-Transmitter (Teilvorhaben in BMBF UTTERMOST; Abschlussbericht; Final report of our activities in BMBF/CATRENE Project UTTERMOST)
Modulation schemes used by >3G mobile communication systems are using rf-signals with high peak to average ratio, thus imposing high challenges to the design of energy-efficient rf-power amplifiers. Additionally the increasing number of various customer requirements and localizations demands for flexible hardware solutions at the same time. Rf-switch mode power amplifiers promise to be a good answer to these challenges. Their successful realization and performance however depends not at last on the modulation format and concept which has been chosen for sampling the rf-signal. Our activities are concentrating on the identification and exploration of modulator concepts which are optimally suitable for energy-efficient rf-signal amplification at low signal distortion being conformal to the requirements of the mobile communication standards. In order to develop and explore new system level modulator concepts we performed extensive simulations and lab-measurements using a dedicated simulation platform which has been built and tailored to that specific purpose. At this a combination of delta-sigma pre-sampling of the baseband signal followed by a quantized rf- pulse width modulation with inherent up-conversion of the wanted signal to the rf-carrier frequency represented the most promising approach. The critical component in this concept was a 28nm CMOS based pulse generator IC which was designed by our project partner INT and processed at Global Foundries. We integrated this chip into a dedicated FPGA-based testbed for successful demonstration and characterization of the system concept. At the end of the project we demonstrated an easy implementable, flexible, and fully digital modulation concept for controlling energy-efficient rf-switch mode amplifiers (fC=983 MHz) which is characterized by high signal quality (2.8%EVM) at 34.7% coding efficiency and low out-of-band emissions (ACLR1 54dB, ACLR2 49.8db). The results will be used when defining concepts for future base stations. The next envisaged step towards industrial exploitation is the feasibility investigation of integrating the above mentioned IC with additional functions into a system on chip. (SoC).