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Author

Prabu Sankar

Other affiliations: Indian Institutes of Technology
Bio: Prabu Sankar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Delta-sigma modulation & Operational amplifier. The author has an hindex of 7, co-authored 9 publications receiving 355 citations. Previous affiliations of Prabu Sankar include Indian Institutes of Technology.

Papers
More filters
Journal ArticleDOI
TL;DR: The converter, designed in a 0.18 mum CMOS technology, achieves a dynamic range of 93.5 dB in a 24 kHz bandwidth and dissipates 90 muW from a 1.8 V supply.
Abstract: We present design considerations for low-power continuous-time modulators. Circuit design details and measurement results for a 15 bit audio modulator are given. The converter, designed in a 0.18 mum CMOS technology, achieves a dynamic range of 93.5 dB in a 24 kHz bandwidth and dissipates 90 muW from a 1.8 V supply. It features a third-order active-RC loop filter, a very low-power 4-bit flash quantizer, and an efficient excess-delay compensation scheme to reduce power dissipation.

128 citations

Journal ArticleDOI
TL;DR: The “assisted opamp” integrator is introduced, which is a way of achieving low distortion operation with low power consumption and circuit implementations of the technique for single-bit modulators using NRZ and switched-capacitor-resistor feedback DACs are presented.
Abstract: The opamp in the first integrator of a high resolution single-bit continuous-time modulator has stringent slew rate requirements, which increases power dissipation. We introduce the “assisted opamp” integrator, which is a way of achieving low distortion operation with low power consumption. We present circuit implementations of our technique for single-bit modulators using NRZ and switched-capacitor-resistor (SCR) feedback DACs. Audio modulators designed in a 0.18 μm CMOS technology are used as vehicles to demonstrate the effectiveness of our techniques. The modulator with an NRZ DAC achieves a dynamic range of 92.5 dB in a 24 kHz bandwidth and dissipates 110 μW from a 1.8 V supply. A second design, which employs an SCR-DAC, achieves a dynamic range of 91.5 dB and dissipates 122 μW. The figures of merit (FOM) of these modulators, 175.9 dB and 174.4 dB respectively, are comparable with those of state-of-the-art multibit designs.

84 citations

Journal ArticleDOI
TL;DR: The Gm-assisted OTA-RC technique is explored, which is a way of combining GM-C and active-RC integrators in a manner that enhances the linearity and speed of the latter, while adding negligible extra noise or power dissipation.
Abstract: The linearity of conventional active-RC filters is limited by the operational transconductance amplifiers (OTAs) used in the integrators. Transconductance-capacitance (Gm-C) filters are fast and can be linear- however, they are sensitive to parasitic capacitances. We explore the Gm-assisted OTA-RC technique, which is a way of combining Gm-C and active-RC integrators in a manner that enhances the linearity and speed of the latter, while adding negligible extra noise or power dissipation. Measurements from a fifth-order Chebyshev filter with 20 MHz bandwidth, designed in a 0.18 μ m CMOS process, demonstrate the efficacy of Gm-assistance in an active-RC integrator.

66 citations

Journal ArticleDOI
TL;DR: It is shown that integrator nonlinearity results in an increased in-band noise (IBN) floor when a multibit quantizer is used in the loop, and analytical relations for the IBN spectral density for several opamp topologies are developed.
Abstract: We analyze the effect of nonlinearity in the first integrator of a single-loop multibit continuous-time delta-sigma modulator, when the loop filter is of the cascade of integrators with feedforward kind. When a multibit quantizer is used in the loop, we show that integrator nonlinearity results in an increased in-band noise (IBN) floor. We develop analytical relations for the IBN spectral density for several opamp topologies, assuming that the shaped quantization noise is approximately Gaussian. Our results agree well with macromodel and transistor level simulations.

45 citations

Proceedings ArticleDOI
10 Nov 2009
TL;DR: The assisted opamp integrator is introduced that addresses the problem of significant power consumption in a low pass continuous-time ΔΣ modulator and achieves 92.5 dB dynamic range in a 24 kHz bandwidth and dissipates 110 µW from a 1.8V supply.
Abstract: The first integrator in a low pass continuous-time ΔΣ modulator normally consumes significant power due to stringent noise and linearity requirements, especially in single-bit designs. We introduce the “assisted opamp integrator” that addresses this problem. The efficacy of our technique is borne out by measurements from a 15 bit audio converter designed in a 0.18 µm CMOS technology. It achieves 92.5 dB dynamic range in a 24 kHz bandwidth and dissipates 110 µW from a 1.8V supply. The Figure of Merit (FOM) of this modulator is 66.5 fJ/level.

22 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: A review of the state of the art on nanometer CMOS implementations is described, giving a survey of cutting-edge ΣΔ architectures, with emphasis on their application to the next generation of wireless telecom systems.
Abstract: This paper presents a tutorial overview of ΣΔ modulators, their operating principles and architectures, circuit errors and models, design methods, and practical issues. A review of the state of the art on nanometer CMOS implementations is described, giving a survey of cutting-edge ΣΔ architectures, with emphasis on their application to the next generation of wireless telecom systems.

235 citations

Book
01 Feb 2010
TL;DR: In this paper, the authors lay a foundation in device physics, noise, and feedback systems including nano scales in a highly original fashion, emphasizing intuitive thinking, and identify ten fundamental principles that are common in both biology and electronics, analog and digital design.
Abstract: Part I. Foundations: Ten chapters lay a foundation in device physics, noise, and feedback systems including nano scales in a highly original fashion, emphasizing intuitive thinking. This foundation is important in designing and analyzing ultra-low-power systems in both electronics and biology Part II. Low-Power Analog and Biomedical Circuits: Five chapters present building-block circuits that are useful for ultra-low-power biomedical electronics and analog electronic systems in general Part III. Low-Power RF and Energy-Harvesting Circuits for Biomedical Systems: Three chapters provide an in-depth description of energy-efficient power and data radio-frequency (RF) links that are fundamental to biomedical systems Part IV. Biomedical Electronic Systems: Two chapters provide an in-depth look at ultra-low-power implantable electronics and ultra-low-power noninvasive electronics for biomedical applications, respectively. Case studies for cochlear implants for the deaf, brain implants for the blind and paralyzed, wearable cardiac devices, and biomolecular sensing are provided Part V. Principles for Ultra-Low-Power Analog and Digital Design: Two chapters discuss principles for ultra-low-power digital design and ultra-low-power analog and mixed-signal design, respectively. The chapters identify ten fundamental principles that are common in both biology and electronics, analog and digital design Part VI. Bio-Inspired Systems: A chapter on neuromorphic electronics discusses electronics inspired by neurobiology followed by a chapter that discusses a novel form of electronics termed Cytomorphic Electronics, electronics inspired by cell biology. These chapters discuss applications of bio-inspired systems to engineering and medicine, deep connections between chemistry and electronics, and provide a unifying viewpoint of ultra-low-power design in biology and in electronics Part VII. Energy Sources: A chapter on batteries and electrochemistry discusses how batteries work from a unique circuit viewpoint. The last chapter discusses energy harvesting in biomedical systems at portable scales (vibration and body heat) and at larger scales (low-power cars and solar cells). Principles of low-power design are shown to extend from small scales in electronics to larger scales and to non-electrical systems. This book reveals the deep connections between energy use and energy generation, vital for sustainable energy systems of the future.

218 citations

Journal ArticleDOI
TL;DR: A detailed analysis on the most recently published compensation techniques for single-stage modulators is performed, thus enabling their application to an arbitrary modulator, and results indicate that a compensation of ELD in every stage of the cascade is insufficient for optimal performance.
Abstract: Excess loop delay (ELD) is well known for its detrimental effect on the performance and stability of continuous-time sigma-delta modulators. A detailed analysis on the most recently published compensation techniques for single-stage modulators is performed in this paper, thus enabling their application to an arbitrary modulator. Based on different characteristics such as circuit complexity, achievable dynamic range, or requirements on the operational amplifiers, their advantages and disadvantages are investigated. Subsequently, the analysis is extended to cascaded modulators. Contrary to intuition, the results indicate that a compensation of ELD in every stage of the cascade is insufficient for optimal performance. Although not configured in a feedback configuration and as such not suffering from stability problems, each coupling network between two stages must additionally be compensated for ELD.

130 citations

Journal ArticleDOI
TL;DR: The converter, designed in a 0.18 mum CMOS technology, achieves a dynamic range of 93.5 dB in a 24 kHz bandwidth and dissipates 90 muW from a 1.8 V supply.
Abstract: We present design considerations for low-power continuous-time modulators. Circuit design details and measurement results for a 15 bit audio modulator are given. The converter, designed in a 0.18 mum CMOS technology, achieves a dynamic range of 93.5 dB in a 24 kHz bandwidth and dissipates 90 muW from a 1.8 V supply. It features a third-order active-RC loop filter, a very low-power 4-bit flash quantizer, and an efficient excess-delay compensation scheme to reduce power dissipation.

128 citations

Journal ArticleDOI
TL;DR: This work gives a method for stabilizing a single-bit continuous-time delta-sigma modulator that uses an FIR feedback DAC and shows that increasing the number of taps beyond a certain number does not improve performance.
Abstract: Single-bit continuous-time delta-sigma modulators (CTDSM) using FIR feedback DACs inherit the appealing aspects of both single-bit and multibit designs, without the disadvantage of either approaches. In this work, we give a method for stabilizing a CTDSM that uses an FIR feedback DAC. Further, we show that increasing the number of taps beyond a certain number (dependent on the architecture and oversampling ratio of the modulator) does not improve performance. The results of our analysis are incorporated in the design of a third-order audio CTDSM which achieves a peak A-weighted SNR of 102.3 dB (raw SNR of 98.9 dB) and a spurious-free dynamic range of 106 dB in a 24 kHz bandwidth, while consuming only 280 μW from a 1.8 V supply.

104 citations