A Switched Capacitor-Based SAR ADC Employing a Passive Reference Charge Sharing and Charge Accumulation Technique
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A Switched Capacitor-Based SAR ADC Employing a Passive Reference Charge Sharing and Charge Accumulation Technique Sreenivasulu Polineni1
· M. S. Bhat1 · S. Rekha1
Received: 25 February 2020 / Revised: 20 April 2020 / Accepted: 22 April 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this work, a switched capacitor-based successive approximation register (SAR) analog-to-digital converter (ADC) using a passive reference charge sharing and charge accumulation is proposed. For N -bit resolution, the fully differential version of this architecture needs only 6 capacitors, which is a significant improvement over conventional binary-weighted SAR ADC. The proposed SAR ADC is first modeled in MATLAB, and the effect of practical operational transconductance amplifier limitations such as finite values of gain, unity-gain bandwidth and slew rate on ADC characteristics is verified through behavioral simulations. To validate the proposed ADC performance, an 11-bit 2 kS/s SAR ADC is designed and laid out in UMC 180 nm 1P6M CMOS technology with a supply voltage of 1.8 V. The total design occupies an area of 568 µm × 298 µm and consumes a power as less as 0.28 µW. It is found that the integral nonlinearity and differential nonlinearity of this ADC are in the range + 0.35/− 0.84 least significant bit (LSB) and + 0.1/− 0.6 LSB, respectively. In addition, dynamic performance test shows that the proposed SAR ADC offers an effective number of bits of 10.14 and a Walden figure of merit (FoMW) of 0.12 pJ/conv-step. Keywords Analog-to-digital converter (ADC) · Biomedical · Passive charge sharing · Folded cascode operational transconductance amplifier (FC OTA) · Successive approximation register (SAR) · Switched capacitor
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Sreenivasulu Polineni [email protected] M. S. Bhat [email protected] S. Rekha [email protected]
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Department of ECE, National Institute of Technology Karnataka, Surathkal 575025, India
Circuits, Systems, and Signal Processing
1 Introduction The analysis of biomedical signals plays a crucial role in determining various disorders in medical science. Also, with the increased prevalence of chronic diseases over the past decade, the need to track biomedical signals continuously in health and wellness management is steadily increasing [25,30]. Together with advancements in electronic manufacturing techniques, the enormous market demand has accelerated the development of power-efficient and miniaturized wearable sensors for biomedical applications. The advanced digital technologies implement most of the signal processing functions, while restricting analog circuits to basic blocks such as amplification, filtering and supply references. This digital revolution has driven the need for analog-to-digital converters (ADCs) in every electronic gadget. In the literature, a wide variety of ADC architectures [16,19] have been reported considering contrasting metrics of speed, resolution and power efficiency. Any ADC must be power efficient in the context of remote patient monitoring
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