Linear Interpolation D/A Converter Applied to Direct Digital RF Modulators

Abstract: This thesis deals with techniques for the full integration of radio frequency (RF) transmitter with CMOS technology. The theory and implementation of high performance digital-to-analog converters (DACs) for radio frequency (RF) transmitters have been studied. A linear interpolation DAC architecture is proposed. By employing the linear interpolation, the attenuation of DAC's image components is significantly increased. The proposed linear interpolation DAC has been applied to direct digital quadrature modulators. The reconstruction filter, usually employed after the DAC in modulators to remove the image components, is eliminated due to this linear interpolation DAC's high attenuation to the image components. Therefore, the costly discrete components are reduced, and the system-onchip (SOC) design can be realized conveniently. A CMOS current injection direct digital RF quadrature modulator and A CMOS current-folded direct digital RF quadrature modulator have been implemented. In the architecture of current injection direct digital RF quadrature modulator, the DAC's differential current signals are directly fed to the mixer, which improves the linearity of the modulated RF signal. In the architecture of current-folded direct digital RF quadrature modulator, the DAC's differential current signals are fed to the mixer by current-folded structures, which realize the low voltage design and improves the linearity of the modulated RF signal also. The proposed modulators generate quadrature modulated RF signals directly and are able to operate with different types, constant and non-constant envelope, of modulations.