Analog Front End of Ecg

Topics: Digital signal processing, Signal processing, Low-pass filter Pages: 19 (4794 words) Published: April 4, 2013
Application Report
SBAA160A – March 2009 – Revised April 2010

Analog Front-End Design for ECG Systems Using Delta-Sigma ADCs Karthik Soundarapandian, Mark Berarducci ......................................................... Data Acquisition Products ABSTRACT This document discusses the characteristics of electrocardiogram (ECG) signals and different front-end approaches for ECG signal acquisition. The tradeoffs between different approaches and the effects on overall system design are discussed. The report also includes descriptions of potential implementations of the front-end architecture using the ADS1258 and ADS1278 and respective noise measurement results.

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Contents Introduction .................................................................................................................. 1 Nature of the ECG Signal and System Design Implications .......................................................... 2 System Approaches ........................................................................................................ 3 ECG AFE with Low-Resolution (≤ 16-bit) ADCs ........................................................................ 4 Simplified Low-Cost ECG AFE with 24-bit Delta-Sigma ADCs ....................................................... 5 Sequential Sampling Measurements with the ADS1258 .............................................................. 7 Simultaneous Sampling Measurements with the ADS1278 ........................................................... 9 References ................................................................................................................. 10 List of Figures

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ECG Signal Characteristics ................................................................................................ 2 System Approaches Based on ADC Resolution ........................................................................ 3 Typical SAR-Based ECG Signal Chain (Sequential Sampling) ....................................................... 4 ΔΣ-Based, Low-Cost ECG Signal Chain (Sequential Sampling) ..................................................... 5 ΔΣ-Based, Low-Cost ECG Signal Chain (Simultaneous Sampling) .................................................. 6 Test Setup Using the ADS1258 ........................................................................................... 7 Measured Time Domain Data ............................................................................................. 8 Test Setup Using the ADS1278 ........................................................................................... 9 ADS1278 with Simulated 2-mV Cardiac Test Input ................................................................... 10

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Introduction
Electrocardiogram (ECG) system analog front-end (AFE) devices are typically designed with discrete off-the-shelf components from various semiconductor vendors or custom-designed as application-specific integrated circuits (ASICs). The costs of an ASIC design could run into millions of dollars by the time the device reaches full production, and may not be practical for many small- and medium-sized companies. The primary components of a traditional discrete ECG AFE include instrumentation amplifiers, operational amplifiers that implement active filters, and analog-to-digital converters (ADCs).

All trademarks are the property of their respective owners. SBAA160A – March 2009 – Revised April 2010 Submit Documentation Feedback Analog Front-End Design for ECG Systems Using Delta-Sigma ADCs Copyright © 2009–2010, Texas Instruments Incorporated

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Nature of the ECG Signal and System Design Implications

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Recent technology advancements have resulted in ADCs with a combination of speeds, resolution, and power that were impossible before. At the same time, the necessity for low-cost and low-power ECG machines has increased, imposing constraints on engineers and...

References: 1. Webster, J.G. (1998). Medical instrumentation: Application and design (3rd edition). New York: Wiley and Sons. 2. Norsworthy, S.R., Schreier, R.S., and Temes, G.C. (1997). Delta-sigma data converters: Theory, design and simulation. New York: IEEE Press. 3. ADS1258: 16-Channel, 24-Bit Analog-to-Digital Converter. Product data sheet SBAS297C. Available for download at www.ti.com/ads1258. 4. ADS1278: Octal, 128-kHz, Simultaneous Sampling 24-Bit Delta-Sigma Analog-to-Digital Converter. Product data sheet SBAS367C. Available for download at www.ti.com/ads1278.
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Analog Front-End Design for ECG Systems Using Delta-Sigma ADCs
Copyright © 2009–2010, Texas Instruments Incorporated
SBAA160A – March 2009 – Revised April 2010 Submit Documentation Feedback
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