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Oversampled analog-to-digital converters based on second-order sigma-delta (XA) modulation are attractive for VLSI implementation because they are especially tolerant of circuit nonidealities and component mismatch. These converters exploit the low parasitic capacitances and small feature sizes characteristic of scaled VLSI technologies by trading speed for resolution. This paper compares the second-order XA modulator to several alternative modulator architectures in the context of digital-audio signal acquisition. Design details and experimental results are presented for a 1-pm CMOS implementation that does not require error correction or component trimming to achieve virtually ideal 16-b performance at a conversion rate of 50 kHz. Tbe experimental modulator is a fully differential circuit that operates from a single 5-V power supply and does not require the use of precision sample-and-hold circuitry. With an oversampling ratio of 256 and a clock rate of 12.8 MHz, tbe modulator achieves a 98-dB dynamic range and a peak signal-to-(noise+ distortion) ratio (SNDR) of 94 dB. Measurements and simulations of discrete noise peaks in the output spectrum that result from limit-cycle oscillations are also presented and discussed.

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