A 0.1 mm$^{2}$, Wide Bandwidth Continuous-Time $SigmaDelta$ ADC Based on a Time Encoding Quantizer in 0.13 $mu$m CMOS
Prefasi, E.
Hernandez, L.
Paton, S.
Wiesbauer, A.
Gaggl, R.
Pun, E.
Electron. Technol. Dept., Carlos III Univ., Leganes, Spain;
This paper appears in: Solid-State Circuits, IEEE Journal of
Publication Date: Oct. 2009
Volume: 44,
Issue: 10
On page(s): 2745-2754
ISSN: 0018-9200
INSPEC Accession Number: 10880529
Digital Object Identifier: 10.1109/JSSC.2009.2027550
Current Version Published: 2009-09-22
Abstract
The ADC shown in this paper uses an innovative sigma-delta (SigmaDelta) architecture that replaces the flash quantizer and mismatch corrected DAC of a multibit continuous time (CT) modulator by a time domain encoder similar to a PWM modulator to reduce the effective ADC area. The modulator achieves the resolution of a multibit design using single bit circuitry by concentrating most of the quantization error energy around a single frequency, which is afterwards removed, seizing the zeros of a sinc decimation filter. The non flat error spectrum is accomplished by use of two filter loops, one of which is made to operate in a self-oscillating mode. An experimental CT-SigmaDelta ADC prototype has been fabricated in 0.13 mum CMOS which implements a third order modulator with two operating modes. Measurements show an effective number of bits (ENOB) of 10 bits and 12 bits in a signal bandwidth of 17 MHz and 6.4 MHz, respectively, and a power-efficient figure of merit (FoM = Pwr/2 middot BW middot 2ENOB) of 0.48 pJ/conversion at 1.5 V supply. The active area of the ADC is 0.105 mm2.
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