A 1 GHz CMOS current-folded direct digital RF quadrature modulator

This paper describes a CMOS current-folded direct digital RF quadrature modulator, which uses two 10-bit linear interpolation current steering digital-to-analog converters (DACs) and two current-folded double-balanced mixers. The attenuation of the DAC image components is significantly increased with linear interpolation, and the reconstruction filter is therefore eliminated. The DAC baseband differential current signals are fed to the mixer by current-folded structures, which realize the low voltage design and improve the linearity of the modulated RF signal. The chip has been implemented with a 0.35 /spl mu/m, double-poly and triple-metal CMOS process.