Non Volatile and Battery-Less Analog Recording of Physiological Signals Using a Low-Cost Device for Voice Signal Storage: A Feasibility Test

Abstract

The ChipCorder ® technology employs a non volatile analog recording technique based on EEPROM technology (i. e. although the signal is time-sampled, its analog voltage is stored in memory cells based on capacitors). This technology provides low-cost voice signal storage devices, which use a sampling frequency (f s) of ¿6.4 kHz to achieve a storage time (t s) of several seconds. Theoretically, reducing f s should allow a proportional increase in t s, which could be used to record physiological signals, which have a lower frequency range. However, the manufacturer points out that at certain low sampling frequencies, the analog voltage stored in the capacitors could drop to an unacceptable level. For this reason, we designed a feasibility test in order to assess the potential of the ChipCorder ® technology for processing and storing physiological signals. An electrocardiogram signal (ECG) (0.7-100 Hz bandwidth) was recorded and played back using the ISD1210P (Information Storage Devices, CA, USA), reducing f s from 6.4 kHz to 25 Hz and hence augmenting t s from 10 to 2526 s. The results showed that the ECG signal was considerably distorted when f s was lower than 200 Hz (t s higher than 320 s). This distortion was due to the aliasing effect, and not to an unacceptable drop in the analog voltage stored in the capacitors. These results suggest that the ChipCorder ® technology could be used to design non volatile recording systems for physiological signals of up to several minutes duration, reducing the complexity and cost as compared with systems based on digital techniques. © 2011 Biomedical Engineering Society.