A 2.5-V sigma-delta modulator for broadband communications applications

Abstract

Oversampled sigma-delta (61) modulators offer numerous advantages for the realization of high-resolution analogto-digital (A/D) converters. This paper explores how oversampling and feedback can be employed in high-resolution 61 modulators to extend the signal bandwidth into the range of several megahertz when the oversampling ratio is constrained by technology limitations. A 2-2-1 cascaded multibit architecture suitable for operation from a 2.5-V power supply is presented, and a linearization technique referred to as partitioned data weighted averaging is introduced to suppress in-band digital-to-analog converter (DAC) errors. An experimental prototype based on the proposed topology has been integrated in a 0.5-m 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.Index Terms-Analog-to-digital conversion, CMOS analog integrated circuits, double sampling, dynamic element matching, integrated circuit design, mixed analog-digital integrated circuits, sampled-data circuits, sigma-delta modulation, switched-capacitor circuits.

A Digital Calibration Technique for the Correction of Glitches in High-Speed DAC's

“…This could e.g. correspond to a DAC clock of 250MHz and a reference high-accuracy ADC sampling at a rate of 2.5MHz which can certainly be achieved with today's Σ∆ modulation technology [5]. However, the calibration principle also works if the calibration ADC is more than a factor 100 slower than the DAC.…”

“…The mean of this digital signal is being subtracted by applying a digital filter. The amplitude of this square wave is the error signal resulting from the difference between the correction pulse and the glitch, and is used to update the correction parameters, according to (5).…”

A continuous-time delta-sigma modulator for 802.11a/b/g WLAN implemented with a hierarchical bottom-up optimization methodology

“…Therefore, they are used for high-accuracy conversions within lower bandwidths like e.g. in UMTS [3]. Besides higher sampling rates, continuous-time (CT) converters on the other hand have additional advantages over DT modulators: no sample-and-hold in front, an inherent anti-aliasing filter and lower thermal noise generation by the filter circuits.…”

On incremental sigma-delta modulation with optimal filtering

“…Σ∆ quantization systems, also known as scalar predictive quantizers or oversampling Analog-to-Digital converters, are widely used in audio systems [1,2] and communication systems [3,4,5]. These systems can achieve very large dynamic range without the need for precise matching of circuit components.…”