The Design of a Delta Sigma Modulator

Presented by: Sameh Assem Ibrahim

24-July-2003

Introduction

Oversampling: fs > 2fm , OSR = fs/2fm > 1

Advantage 1: Relax anti-aliasing filter

Advantage 2: Reduce in-band quantization noise and thus increase SNR

Note that: A quantized signal ampled at (fs) will have all its noise power folded into the frequency band extending from 0 to (fs/2)

The need for delta sigma modulation Nyquist converters:

SNR = 1.76 + 6.02n Overampled:

SNR = 1.76+6.02n+10log(OSR) Solution is Noise shaping

through delta sigma modulators

Proposed Architecture and Specifications

ΣΔ ModulatorAnalog

inputDecimator

Digital

FS

Analog

Output FN

1 bit Multiple bits

Integrator Integrator

1-Bit D/A

+ +

--x(n)

y(n)

fs

Supply Voltage3.3V

Power consumption<130 mW

Input signal BW20 kHz

OSR128

SNR60dB

Reference Voltage2V

Simulink Model

Integrator1 Integrator2

Comparator(1 bit Quantizer)

DACTo achieve stability

Circuit Used

Simulation Results