An automatic gain control circuit to improve ECG acquisition

Marco Rovetta,João Fernando Refosco Baggio,Raimes Moraes

doi:10.1590/2446-4740.04217

Marco Rovetta, João Fernando Refosco Baggio + Show 1 more

Open Access

https://doi.org/10.1590/2446-4740.04217

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Abstract

Abstract Introduction Long-term electrocardiogram (ECG) recordings are widely employed to assist the diagnosis of cardiac and sleep disorders. However, variability of ECG amplitude during the recordings hampers the detection of QRS complexes by algorithms. This work presents a simple electronic circuit to automatically normalize the ECG amplitude, improving its sampling by analog to digital converters (ADCs). Methods The proposed circuit consists of an analog divider that normalizes the ECG amplitude using its absolute peak value as reference. The reference value is obtained by means of a full-wave rectifier and a peak voltage detector. The circuit and tasks of its different stages are described. Results Example of the circuit performance for a bradycardia ECG signal (40bpm) is presented; the signal has its amplitude suddenly halved, and later, restored. The signal is automatically normalized after 5 heart beats for the amplitude drop. For the amplitude increase, the signal is promptly normalized. Conclusion The proposed circuit adjusts the ECG amplitude to the input voltage range of ADC, avoiding signal to noise ratio degradation of the sampled waveform in order to allow a better performance of processing algorithms.

Highlights

Long-term electrocardiogram (ECG) recordings are widely employed to assist the diagnosis of cardiac and sleep disorders
An example of the circuit behavior is shown for a simulated ECG which has a sudden 50% drop of its R wave amplitude (Figure 3)
The ECG signal was generated by means of a digital to analog converter belonging to a commercial microcontroller development board (STM32F429I-DISCO – STMicroelectronics)

Summary

Introduction

Long-term electrocardiogram (ECG) recordings are widely employed to assist the diagnosis of cardiac and sleep disorders. This work presents a simple electronic circuit to automatically normalize the ECG amplitude, improving its sampling by analog to digital converters (ADCs). Conclusion: The proposed circuit adjusts the ECG amplitude to the input voltage range of ADC, avoiding signal to noise ratio degradation of the sampled waveform in order to allow a better performance of processing algorithms. Discrete-time signal processing techniques are commonly applied to electrocardiogram (ECG) signals in order to obtain indices to assist diagnosis of cardiopathies and sleep disorders The performance of such techniques is highly affected by the signal to noise ratio (SNR) of the sampled signals (Elgendi et al, 2014). This work describes a simple electronic circuit to automatically adjust the highest magnitude wave of the ECG to the ADC input range in order to improve resolution and avoid saturation. The proposed circuit contributes to obtain better quality ECG recordings

Methods

Results

Conclusion