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The dual-band recording of the local-field potential (LFP, 0.1-200 Hz) and the spike potential (SP, 200 Hz-10 kHz) is important for physiological studies at the cellular level. Recent study shows that the LFP signal plays important roles in modulating many profound cellular mechanisms. Although various bio-signal acquisition circuits have been reported over the years, few designs are applicable to capture both LFP and SP signals. To record both signals accurately, acquisition circuits need low noise and good linearity in both bands. In this paper, we report the design of a dual-band acquisition IC for microelectrode array (MEA) recording. The novel design uses a continuous-time (CT) front-end with chopping to suppress the noise in the LFP band, and a discrete-time (DT) back-end to achieve good linearity. The acquisition channel is fully differential, which leads to a high common-mode rejection ratio (CMRR) and power supply rejection ratio (PSRR) without the 50 Hz injection. The design interfaces the microelectrode with a transistor gate, which has high input impedance. A prototype monolithic acquisition IC is fabricated in a 0.35 μm CMOS process. It includes 16 channels and an 11 bit successive-approximation (SAR) analog-to-digital converter (ADC). Every channel acquires cellular signals up to 20 mVpp with 32.9 nV/Hz0.5 and <; 0.1% nonlinearity. The good linearity effectively prevents the aliasing and mixing between the two bands. For LFP signal, the recording noise is 0.9 μVrms. For SP signal, the recording noise is 3.3 μVrms. The new design has high input impedance (320 M Ω@1 kHz), high CMRR ( >; 110 dB) and PSRR ( >; 110 dB). The noise-efficiency factor (NEF) of the acquisition channel is 7.6. The IC is experimented to record the field potential from cultured rat cardiomyocytes in-vitro. Overall, the new MEA acquisition channel achieves the state-of-art performance.
Date of Publication: May 2012