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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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