Tuyển tập các báo cáo nghiên cứu về hóa học được đăng trên tạp chí hóa hoc quốc tế đề tài : Multistage Quadrature Sigma-Delta Modulators for Reconfigurable Multi-Band Analog-Digital Interface in Cognitive Radio Devices | Marttila et al. EURASIP Journal on Wireless Communications and Networking 2011 2011 130 EURASIP Journal on . http content 2011 1 130 Wireless Communications and Networking a SpringerOpen Journal RESEARCH Open Access Multistage Quadrature Sigma-Delta Modulators for Reconfigurable Multi-Band Analog-Digital Interface in Cognitive Radio Devices Jaakko Marttila Markus Allén and Mikko Valkama Abstract This article addresses the design analysis and parameterization of reconfigurable multi-band noise and signal transfer functions NTF and STF realized with multistage quadrature ZA modulator QZAM concept and complexvalued in-phase quadrature I Q signal processing. Such multi-band scheme was already proposed earlier by the authors at a preliminary level and is here developed further toward flexible and reconfigurable A D interface for cognitive radio CR receivers enabling efficient parallel reception of multiple noncontiguous frequency slices. Owing to straightforward parameterization the NTF and the STF of the multistage QZAM can be adapted to input signal conditions based on spectrum-sensing information. It is also shown in the article through closed-form response analysis that the so-called mirror-frequency-rejecting STF design can offer additional operating robustness in challenging scenarios such as the presence of strong mirror-frequency blocking signals under I Q imbalance which is an unavoidable practical problem with quadrature circuits. The mirror-frequency interference stemming from these blockers is analyzed with a novel analytic closed-form I Q imbalance model for multistage QZAMs with arbitrary number of stages. Concrete examples are given with three-stage QZAM which gives valuable degrees of freedom for the transfer function design. High-order frequency asymmetric multi-band noise shaping is in general a valuable asset in CR context offering flexible and frequency agile adaptation capability to differing waveforms to be received and .
