Abstract
This article reports on a compact and low-power CMOS readout circuit for bioelectrical signals based on a second-order delta-sigma modulator. The converter uses a voltage-controlled, oscillator-based quantizer, achieving second-order noise shaping with a single opamp-less integrator and minimal analog circuitry. A prototype has been implemented using 0.18 μm CMOS technology and includes two different variants of the same modulator topology. The main modulator has been optimized for low-noise, neural-action-potential detection in the 300 Hz–6 kHz band, with an input-referred noise of 5.0 μVrms, and occupies an area of 0.0045 mm2. An alternative configuration features a larger input stage to reduce low-frequency noise, achieving 8.7 μVrms in the 1 Hz–10 kHz band, and occupies an area of 0.006 mm2. The modulator is powered at 1.8 V with an estimated power consumption of 3.5 μW.
Highlights
Delta-Sigma Modulator for Electrogenic cells, such as neurons, cardiac cells, or retinal cells, generate ionic currents across their membrane owing to the different ion channels that populate the cellular membranes
These voltage signals occur in different frequency bands and feature different amplitudes depending on their nature: neural action potentials (APs) manifest as spikes with amplitudes ranging from a few tens of μV to 1 mV and most signal power between 300 Hz and 6 kHz, whereas cardiac field potentials may reach tens of mV with most signal power in the
In vitro studies can be performed with CMOS microelectrode arrays (MEAs), the electrode array of which is co-integrated with the readout electronics [3]
Summary
Delta-Sigma Modulator for Electrogenic cells, such as neurons, cardiac cells, or retinal cells, generate ionic currents across their membrane owing to the different ion channels that populate the cellular membranes. Transmembrane ionic currents produce voltage variations in the extracellular medium that can be detected by miniaturized sensors in close proximity to the cells These voltage signals occur in different frequency bands and feature different amplitudes depending on their nature: neural action potentials (APs) manifest as spikes with amplitudes ranging from a few tens of μV to 1 mV and most signal power between 300 Hz and 6 kHz, whereas cardiac field potentials may reach tens of mV with most signal power in the. In order to detect APs with acceptable signal-to-noise ratios, recording front-ends require input-referred noise values below 10 μVrms This is especially relevant for neural interfaces, where small action potentials generated by different neurons need to be separated and assigned to the respective signal sources.
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