A 1.8GHz CMOS continuous-time band-pass delta-sigma modulator for RF receivers

This paper presents a new band-pass undersampling delta-sigma modulator dedicated to multigigahertz frequencies. The proposed architecture is based on up-sampling in the feedback path to increase bandwidth of the DAC in the feedback. Because the analog-side IF is different from the digital-side IF in undersampling modulators, conversion of these IFs is a main problem in such design. The DAC used in the feedback path behaves as a lowpass filter that attenuates high frequency replicas of the analog IF. The underlying proposed architecture can receive high frequency carriers modulated with signals of bandwidth as large as 10 MHz modulated at 1.8 GHz. The paper discuss practical considerations that strongly influence the overall performance of this architecture.