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发表于 2012-5-11 14:53:45
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回复 4# fhchen2002
Abstract — Oversampling techniques based on sigma-delta (SD) modulation offer
numerous advantages for the realization of high-resolution analog-to-digital (A/D)
converters in a low-voltage environment. This paper examines the design and
implementation of a CMOS SD modulator for digital-audio A/D conversion that operates
from a single 1.8-V power supply. A cascaded modulator that maintains a large full-scale
input range while avoiding signal clipping at internal nodes is introduced. The experimental
modulator has been designed with fully-differential switched-capacitor integrators
employing different input and output common-mode levels and boosted clock drivers in
order to facilitate low voltage operation. Precise control of common-mode levels, high power
supply noise rejection, and low power dissipation are obtained through the use of two-stage,
class A/AB operational amplifiers. At a sampling rate of 4 MHz and an oversampling ratio
of 80, an implementation of the modulator in a 0.8-mm CMOS technology with metal-topolycide
capacitors and NMOS and PMOS threshold voltages of +0.65-V and –0.75-V,
respectively, achieves a dynamic range of 99 dB at a Nyquist conversion rate of 50 kHz. The
modulator can operate from supply voltages ranging from 1.5 V to 2.5 V, occupies an active
area of 1.5 mm2, and dissipates 2.5 mW from a 1.8-V supply. |
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