Broadband oversampling analog-to-digital conversion for digital communications

The trends towards higher signal bandwidths and increased digital signal processing, evident in both wired and wireless communications systems, have stimulated the development of data conversion interfaces that can be integrated in standard CMOS technologies while meeting stringent resolution and linearity requirements at increasing Nyquist conversion rates. The integration of high-performance analog-to-digital (A/D) converters is further complicated by the reduction in supply voltage dictated by the growing demand for portability and the scaling of VLSI technology.; Oversampled sigma-delta modulators offer numerous advantages for the realization of high-resolution A/D converters and are widely used in low-speed, high-resolution A/D converters for applications such as digital audio. This dissertation explores how oversampling and feedback can be employed effectively in megahertz-bandwidth CMOS A/D converters to extend the resolution and linearity that can be achieved beyond that of Nyquist-rate converters operating at an equivalent conversion rate. The limitations imposed by technology are examined, and techniques such as double sampling and multi-bit quantization are studied in detail to evaluate their suitability for use in megahertz-bandwidth oversampling modulators. This work also introduces a linearization technique referred to as Partitioned Data Weighted Averaging to suppress in-band DAC errors.; A fifth-order cascaded multi-bit modulator, suitable for operation from a 2.5-V supply and capable of digitizing a 2-MHz baseband signal with the quantization noise suppressed by over 100 dB, has been designed, and implementation nonidealities have been considered carefully in order to define the circuit requirements for a power-efficient CMOS implementation.; An experimental prototype based on the proposed topology has been integrated in a 0.5-μm, double-poly, triple-metal CMOS technology. Fully-differential, double-sampled switched capacitor integrators enable the modulator to achieve 95 dB dynamic range at a 4 MSample/s Nyquist conversion rate with an oversampling ratio of 16. The experimental modulator dissipates 150 mW from a 2.5-V supply.