Continuous-time Sigma-Delta Modulator For Low-voltage Low-power Audio Application

The market for portable electronic products is continually expanding, which requires large amount of researches into high-performance low-power electronic systems.For the widely used portable audio electronic systems, SOC (system on chip) solution has been proved to be high-performance and low-cost. With the aggressively scaling technology, low-power design with low supply voltage in SOC application has become a momentous issue.This dissertation focuses on design of high-performance low-voltage low-power audio sigma-delta analog-to-digital converter, which is one of the most important and performance-limiting components in audio electronic systems.In this dissertation, a 1-V third-order single-bit continuous-time (CT) sigma-delta modulator is presented.Compared with traditional discrete-time sigma-delta modulators that utilize switched-capacitor circuits, continuous-time sigma-delta modulators have the advantage of lower power consumption and inherent anti-alias filtering.The presented modulator utilizes active RC integrators to implement the loop filter, and CIFB (chain of integrators with feedback) architecture is adopted in system-level due to its low sensitivity to RC time constant variations.An efficient circuit design methodology based on VerilogA models is proposed and verified for designing continuous-time sigma-delta modulator. System-level and circuit-level design techniques are proposed to deal with problems encountered in low-voltage low-power designs. Moreover, effective load of the Opamp in active RC integrator is deduced and two-stage class A/AB amplifiers are adopted for its superior low power merits. Designed in SMIC mixed-signal 0.13-μm CMOS process, the presented modulator achieves 82.3-dB SNDR and 85-dB dynamic range (DR) within 20-KHz bandwidth.The total power consumption of the modulator is only 60μW from a 1-V power supply and the prototype occupies an active area of only 0.12mm2.