A low noise and low power device composed of electrode and CD ASIC for neural and other vital signals recording

Abstract

In this paper, to effectively record the electroencephalogram (EEG) and other body-vital signals of the healthy volunteer, a low-noise and low-power device was developed. The proposed device consisted of a novel convenient, reliable and sensitive electrode realized by an Ag/AgCl dry-contact electrode coated with nano-composites and a novel post-electrode chopper digitizer (CD). The CD consisted of a low noise and low power chopping pre-amplifier with gain and band-width (BW) adjustable abilities and an intermediate speed and low power successive approximation register-analog digital converter (SAR-ADC). First, using the front-end electrode, the neural signal was received from the brain scalp; second, using the CD, the amplified analog voltage outputting from the chopping pre-amplifier was converted into digital sequences using the SAR-ADC. Testing results showed that the contact resistance between the electrode and the brain scalp was optimized to about 300.00 kΩ, as the electrode was coated with polypyrrole-graphene nano-particles. And, the linear relevancy between the electrode and the traditional wet-contact electrode was more than 93%. Finally, the CD was manufactured with CMOS technology (SmicRF180NM 1Poly6M) under a supply voltage of 1.0 V. Testing results of the CD showed that: (1) the CD achieved an inputting-referred noise of 0.40 μV root-mean-square (RMS) in 0.18–200 Hz, the energy consumption was 3.40 μW for one chopping pre-amplifier, 200 μW for SAR-ADC, etc.; (2) the SAR-ADC achieved an effective number of bits (ENOB) of 9.96-bits under conversion rate reaching 1.00 MSps, the signal noise ratio (SNR) was 60.97 dB, etc. The designed device could satisfy recording for EEG signals in μV level, also, the device could be used for detecting electrocardiography (EKG) signals in mV level. So, the low noise and low power device worked well for recording micro neural signals, and suitable for constructing reliable portable or wearable pervasive bio-devices used for multiple body-vital signals too.