Modeling, Quantitative Analysis, and Design of Switched-Current Pipeline A/D Converters

Abstract

Switched-current (SI) analog-to-digital converters (ADCs) are desirable for biomedical applications. Until now, SI ADCs are lacking effective and systematic computer-aided analysis and design (CAD) tools, particularly for noise. In this paper, models for different SI multiplying-digital-to-analog-converter (MDAC) designs are analytically derived, with the inclusion of distortion and noise. The models can be further programmed into an equation-based SI analog CAD tool. In this paper, the equation-based models (EBMs) are used to quantitatively analyze SI MDACs. Simulation results show that noise significantly limit the performance of SI MDACs. Optimal performance boundaries are derived for single-ended and fully differential SI MDACs. The boundaries from EBMs are consistent with the published SI circuit measurements. A methodology is formulated to design efficient SI MDACs. The EBM and the design methodology are further verified by designs of two sample SI MDACs in an AMS 0.35-m CMOS process with SPICE simulation. Results from the EBM match those from real circuit models well, except for the noise of SI MDACs with feedback, in which case, the design margin should be added to the target performance. For low-/medium-resolution ( 12 bit) applications, a pipeline ADC with a simple SI MDAC is the most efficient. Nonetheless, single-ended SI ADCs are susceptible to source noise. For high-resolution applications, only fully differential SI pipeline ADCs can be selected.Index Terms-Analog computer-aided analysis and design (CAD), distortion, equation based, multiplying digital-to-analog converter (MDAC), noise, pipeline analog-to-digital converters (ADCs), simulation based, switched capacitor, switched current.

A Novel Cyclic Time to Digital Converter Based on Triple-Slope Interpolation and Time Amplification

“…3, respectively [13]. The structure of the time domain 2.5b/stage is similar to a conventional 2.5b multiple digital-to-analog converter (MDAC) which is a main block in voltage domain pipeline and cyclic converters [17], [18]. The time domain 2.5b/stage consists of a TDC, a digital-to-time converter (DTC) and a time amplifier (TA) [19].…”