Delta-Sigma Modulators

Transcription

1 Delta-Sigma Modulators Modeling, Design and Applications George I Bourdopoulos University ofpatras, Greece Aristodemos Pnevmatikakis Athens Information Technology, Greece Vassilis Anastassopoulos University of Patras, Greece Theodore L Deliyannis University of Patras, Greece Imperial College Press

2 Contents Preface v 1. Introduction Modulation - Demodulation AI Modulation Design and Implementation of AS Modulators Applications Book Organization Analog to Digital Conversion Introduction The Basic Concept of A/D Conversion Uniform Sampling Quantization Error and the Linear Model Sampling ofband-pass Signals Oversampling Principles The Delta Modulator Performance of the Delta Modulator The Exponential DM The Concept ofnoise Shaping 36 ix

3 X AS Modulators 2.11Summary 37 Problems 3g 4Q 3. AS Modulators Architectures Introduction 4i 3.2 First-Order AS Modulators Input and output waveforms SNR and PSD diagrams, ' ' Comparison of Delta and AS Modulators Linear DM Exponential DM 4g AS Modulator Second-Order AS Modulators High-Order AS Modulators 5! 3.6 Stability of Single-Stage AS Modulators Multi-Stage AS Modulators Multi-Bit AS Modulators Hybrid AS Modulators Adaptive AS Modulators Band-Pass AS Modulators Summary 73 Problems Single-Bit Single-Stage AS Modulators, Modeling and Design Introduction Modeling of AS Modulators Linear model Quasi-Linear model NTF Characteristics Stability of AS Modulators Stability Criteria g7 4.6 Noise Transfer Function Determination Optimizing the position ofzeros Optimizing the position of poles 93

4 Contents xi 4.7 AS Modulator Assessment Summary 96 Problems Implementation of AS Modulators Introduction Basic Blocks of a AS Modulator for Analog-to-Digital Conversion The loop filter Local ADC and DAC Continuous-Time Loop Filter Implementation Circuit Design ofa First-Order AS Modulator Circuit Design ofa Second-Order AS Modulator Circuit Design of a Third-Order AS Modulator Circuit Design of a Fourth-Order Band-pass AS Modulator Testing the Operation of AS Modulators Experimentally Low-Power, Low-Voltage AS Modulators Summary 134 Problems Appendix Practical Limitations of AS Modulators Introduction Practical Circuit Limitations Noise sources in the AS loop Effect of Thermal Noise SCcircuits CT active RC circuits Effects of the Opamp Non-ldealities Thermal and flicker noise and DC offset of the opamp Finite opamp gain Finite bandwidth and slew-rate of the opamp

5 xii AS Modulators 6.5 Effect ofjitter, SCcircuits, CT active RC circuits i Effect of Rise and Fall Times of DAC Pulses in CT Circuits, <- fi 6.7 A Comparison of SC and CT active RC Circuits DACErrors Single-bit DAC Multibit DAC.. i AI 6.9 Summary,,., Problems Stabilization and Suppression of Tones for Higher-Order Single-Stage AS Modulators Introduction 7.2 Bounds on Quantizer Input Using the Variable Gain Method g 7.3 Stabilization Methods 1 y Resetting the integrators Clipping the integrators Activation of local feedback loops around the integrators y] Reducing the order of the loop filter Comparison of the Stabilization Methods Tones in AS Modulators Fixed Techniques ^ Dithering Chaotic AS modulators Bit-flipping 18g Comparison of fixed techniques Adaptive Techniques Adaptive dithering Adaptive bit-flipping Comparison of the adaptive techniques 193

6 Contents xiii 7.8 Summary Decimation, Interpolation and Converters 8.1 Introduction 8.2 Rate Conversion Decimation QS Interpolation 8 3 Decimation and Interpolation filters 201?rv3 ZUJ> Multi-stage rate conversion LVJ Comb filters Fractional rate conversion AS Modulators for ADC AI Modulators for DAC Summary Problems Applications 9.1 Introduction AI Modulation in Digital Radio Conversion bandwidth and resolution Sampling rate Frequency Synthesis Principles of the PLL Operation AI modulation in frequency synthesis Analysisof the frequency divider Clock Generators Using AI Modulation AI Modulation in Analog-Input Digital Phase-Locked Loops for Frequency and Phase Demodulation AI Modulation in Analog Oscillators Summary Index