The building blocks of wireless communication radio transmitters are encountering new design challenges due to the digital-driven evolution of CMOS technology. The continuously decreasing voltage headroom challenges the traditional circuit topologies, while the speed increase of the transistors enables new circuit innovations to benefit from the technology trend. In addition, the tendency of digitizing the analog functions in the transmitter signal chain pushes the digital/analog interface towards the antenna. The research work presented in this thesis concentrates on this challenge by introducing a new transmitter architecture, direct-digital RF modulator, which brings the D/A conversion in front of the power amplifier (PA). The thesis has three focus areas: D/A converter, IQ modulator, and direct-digital RF modulator. The research work summarizes the practical design considerations in order to provide the background knowledge and means required for the new transmitter architecture, which is based on combining the D/A conversion and IQ modulation into a single circuit block. The work is demonstrated with five circuit implementations that all focus on different aspects of the proposed architecture. The first two outline the key performance constrains of D/A converters. In order to overcome the limited matching performance of the transistors, a new DC linearity calibration technique was developed. The third circuit implementation demonstrates a direct conversion transmitter architecture targeted for a wide bandwidth radio system. The last two circuit implementations demonstrate the proposed transmitter architecture, which is constructed with two digital-to-RF converters performing quadrature modulation. In the introduced converter topology the D/A conversion and the up-conversion are applied for each of the unit digital signals individually, converting the input signal directly to the final frequency. Finally, the applicability of the architecture to a multi-standard radio transmitter was investigated by measuring the performance with signal vectors of different cellular and connectivity radio standards.
|Translated title of the contribution||Suora digitaalinen RF-modulaattori usean standardin radiolähettimiin|
|Publication status||Published - 2014|
|MoE publication type||G4 Doctoral dissertation (monograph)|
- D/A converter
- IQ modulator
- direct-digital RF modulator