A digital-to-RF converter (DRFC) architecture for IQ modulator is proposed in this paper. The digital-RF converter utilizes the mixer DAC concept but a discrete-time oscillatory signal is applied to the digital-RF converter instead of a conventional continuous-time LO. The architecture utilizes a low pass Σ∆ modulator and a semi-digital FIR filter. The digital Σ∆ modulator provides a single-bit data stream to a current-mode SDFIR filter in each branch of the IQ modulator. The filter taps are realized as weighted one-bit DACs and the filter response attenuates the out-of-band shaped quantization noise generated by the Σ∆ modulator. To find the semi-digital FIR filter response, an optimization problem is formulated. The magnitude metrics in out-of-band is set as optimization constraint and the total number of unit elements required for the DAC/mixer is set as the objective function. The proposed architecture and the design technique is described in system level and simulation results are presented to support the feasibility of the solution.
Papers A and C are reprinted with permission from IEEE.Cover figure is an illustration of the digital cascaded error-feedback modulator.Printed by LiU-Tryck, Linköping, Sweden 2014 To my parents and teachers
AbstractA number of state-of-the-art low power consuming digital delta-sigma modulator (∆Σ) architectures for digital-to-analog converters (DAC) are presented in this thesis. In an oversampling ∆Σ DAC, the primary job of the modulator is to reduce the word length of the digital control signal to the DAC and spectrally shape the resulting quantization noise. Among the ∆Σ topologies, error-feedback modulators (EFM) are well suited for so called digital to digital modulation In order to meet the demands, various modifications to the conventional EFM architectures have been proposed. It is observed that if the internal and external digital signals of the EFM are not properly scaled then not only the design itself but also the signal processing blocks placed after it, may be over designed. In order to avoid the possible wastage of resources, a number of scaling criteria are derived. In this regard, the total number of signal levels of the EFM output is expressed in terms of the input scale, the order of modulation and the type of the loop filter.Further on, it is described that the architectural properties of a unit elementbased DAC allow us to move some of the digital processing of the EFM to the analog domain with no additional hardware cost. In order to exploit the architectural properties, digital circuitry of an arbitrary-ordered EFM is split into two parts: one producing the modulated output and another producing the filtered quantization noise. The part producing the modulated output is removed after representing the EFM output with a set of encoded signals. For both the conventional and the proposed EFM architectures, the DAC structure remains unchanged. Thus, savings are obtained since the bits to be converted are not accumulated in the digital domain but instead fed directly to the DAC.A strategy to reduce the hardware of conventional EFMs has been devised recently that uses multiple cascaded EFM units. We applied the similar approach but used several cascaded modified EFM units. The compatibility issues among the units (since the output of each proposed EFM is represented by the set of encoded signals) are resolved by a number of architectural modifications. The digital processing is distributed among each unit by splitting the primary input bus. It is shown that instead of cascading the EFM units, it is enough to cascade their loop filters only. This leads not only to area reduction but also to the reduction of power consumption and critical path.All of the designs are subjected to rigorous analysis and are described mathev vi Abstract matically. The estimates of area and power consumption are obtained after synthesizing the designs in a 65 nm standard cell library provided by the foundry.
Populärvetenskaplig sammanfattning vii viiiPopulärvetenskaplig sammanfattning I denna avhandling presenteras e...
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