Browsing by Author "Elsayed, Fahmi"

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    Multi-level Delta Sigma Modulator Based Transmitters for GHz Wireless Radio Systems
    (2014-05-02) Elsayed, Fahmi; Ghannouchi, Fadhel; Helaoui, Mohamed
    The delta sigma modulator (DSM) based transmitter is a promising architecture that is suitable for multi-standard wireless applications. The conventional DSM-based transmitter suffers from low overall power efficiency due to the low coding efficiency (CE) of the used two-level DSM circuits. Different approaches are reported in literature to improve the efficiency of DSM-based transmitters with the aim of being competitive with other amplification architectures. Most of the reported architectures suffer from two limitations. First, a fully digital pre-distorter is required to improve the linearity of the transmitter. This increases the complexity of the digital signal processing block and limits the applicability of these architectures for wireless mobile terminals. Second, they have a limited frequency bandwidth. In order to improve the performance of the DSM circuit, a new multi-level complex delta sigma modulator circuit is proposed. A study of different DSM circuits is performed. The study includes Cartesian, envelope and the proposed complex DSM circuits with different circuit orders and different quantization levels. Based on the proposed multi-level complex DSM, three new multi-level DSM-based transmitter architectures are proposed. The first architecture is a linearized single branch multi-level DSM-based transmitter. The linearity is achieved through a new simple linearization algorithm, which is proposed to replace a fully digital pre-distorter. Then, a novel dual-branch DSM-based transmitter is proposed as the second architecture. The proposed transmitter architecture is implemented using a new technique, namely three-level de-multiplexed DSM based transmitter. The transmitter has both a high power efficiency and a high linearity without linearization schemes. The third transmitter implementation is a wideband dual-branch three-level DSM-based transmitter. The transmitter is based on two broadband power amplifiers that are connected in back-to-back configuration. Eventually, a new noise reduction technique is reported to improve the adjacent channel power ratio (ACPR) of the transmitted signal.