Modulation and frequency synthesis for wireless digital radio

A new wideband modulator architecture, that is suitable for continuous-phase constant-envelope modulation schemes, is presented in this thesis. The technique is based on direct modulation of a high resolution DeltaSigma frequency discriminator based synthesizer to produce the modulated RF signal without up-conversion. The advantage of this architecture is that it does not require mixers or D/A converters to generate the In-phase and Quadrature signals as in conventional GMSK modulators. This eliminates many of the analog problems associated with mixing and filtering and results in an architecture suitable for monolithic integration.;A high modulation data rate is possible, without sacrificing phase noise performance, through digital equalization of the synthesizer closed-loop response. A digital GMSK transmit filter pre-shapes the data symbols and additionally compensates for the synthesizer closed-loop response. This permits the use of a narrower synthesizer bandwidth to attenuate the DeltaSigma quantization noise, while equalization effectively widens the modulation bandwidth to handle high data rates. The digital equalization filter adds little complexity to the transmitter architecture, since it is combined with the Gaussian data filter. Matching between the transmit filter and the synthesizer closed-loop response is not an issue since the loop parameters are digitally defined and are therefore predictable.;An experimental GSM modulator operating at 2GHz was developed to validate the suitability of the architecture for use in wireless communication systems. It makes use of a custom BiCMOS DeltaSigma frequency discriminator chip that is a key component in the modulator architecture.