| Summary: | 博士 === 國立成功大學 === 電機工程學系碩博士班 === 94 === Bandpass Sigma-Delta Modulators (BPSDMs) with a high dynamic range (DR) are a good solution for an intermediate frequency (IF) analog-to-digital converter (ADC). A high-order structure and a multi-bit internal quantizer resolution allows the BPSDM to have a high DR at a lower oversampling ratio (OSR).
Single-stage high-order structures are used for the BPSDM design in the research. Popular single-stage structures for BPSDMs include cascade-of-resonator with distributed feedback (CRFB), and cascade-of-resonator with distributed feedforward (CRFF). The two structures have a larger coefficient spread, especially when quality factor (Q) is high. A low-spread cascade-of-resonator with a distributed feedforward (LSCRFF) structure for high-order BPSDMs is presented in this thesis to significantly reduce coefficient spread problems. The coefficient spread can therefore be reduced, resulting in the reduced capacitance area in switched-capacitor BPSDM circuits. With component mismatch, peak signal-to-noise ratio (PSNR) degradation of the proposed structure is less than that of the conventional CRFB and CRFF structures, demonstrating a reduced sensitivity to component mismatch. In addition, the proposed structure also allows the noise transfer function (NTF) and signal transfer function (STF) to be designed independently. The STF can be designed to have sharp bandpass filtering.
Next, the design of optimal coefficients for high-order BPSDMs with single-stage structures is more difficult, involving exhaustive analysis, complicated design tradeoffs, instability problems, and a long design cycle. To improve productivity and time-to-market, design automation tools for BPSDMs are highly desirable. In this thesis, an automatic coefficient design methodology for discrete-time high-order BPSDMs with single-stage structures is presented. The methodology covers many design concerns including BPSDM coefficient tolerances for circuit component mismatch, design tradeoffs in in-band noise suppression, OSR, modulator orders and quantizer bit number. The proposed method succeeds in reducing the exhaustive analysis and the number of iterative simulations when designing high-order BPSDMs. Even for inexperienced designers, reliable and high-tolerance BPSDM coefficients for various applications can be automatically and efficiently generated.
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