Direct RF Sampling Continuous-Time Bandpass Delta-Sigma A/D Converter Design for 3G Wireless Applications

This paper presents a direct RF sampling fourth-order bandpass Delta-Sigma A/D converter for multi-carrier 3G wireless base stations. The ADC directly samples an input signal from a carrier frequency ($f_c$) of 2.1 GHz and converts to a lower IF of 0.7 GHz. We propose a mirrored-image sampling technique, an undersampling technique creating the mirrored image signal at a lower frequency, which can reduce the design complexity, jitter requirement, and power dissipation, in comparison to conventional sampling at $4*f_c$. 

The detailed analysis and simulation of stability and SNR presented in this paper show the feasibility of such an undersampling design by carefully selecting the optimum DAC topology and design parameters. We show that, with an RZ33%-DAC, the ADC is capable of digitizing a 2.1 GHz RF signal of bandwidth 20 MHz at 2.8 GSamples/sec with 87dB SNR.