3Brain BioCAM X, Руководство пользователя

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sufficiently high sampling frequency for each electrode.
In BioChips the local in-pixel buffers underneath each electrode allow to locally adapt signals from high
impedance (electrode-side) to low impedance (wiring-side) to avoid the induction of coupling noise
from electrical wiring before amplification. Additionally, the on-chip multiplexing and addressing circuits
allow to minimize the number of wiring outputs even though the large number of electrodes that have
to be simultaneously measured. Indeed, each electrode signal is not individually wired off-chip. Rather,
signals of multiple electrodes are multiplexed at high frequency over a few number of wires. In this way,
several thousands of electrodes can be recorded on only a few tens of output wires.
The in-pixel circuit implemented in BioChips allows recordings from a large signal bandwidth that
includes field potentials and spikes. Instead of implementing an AC-coupling solution that would require
large areas for the integration of adequate capacitors, the BioChips in-pixel circuit integrates an au
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to-zeroing circuit that is regularly calibrated to the electrode DC voltage and that subtracts this cali-
brated DC voltage from the electrode signal before the first amplification stage. This process is called
calibration and it also allows to adapt the circuit performance to different experimental conditions. In
particular, all CMOS devices are photosensitive and photo-generated charges give rise to different DC
drifting times that can bring in-pixel amplifiers to saturate. BioChips mitigate these effects and hence
allow experiments under light stimulation conditions (as required for instance for retina stimulation) by
using higher calibration frequencies to keep the DC input signal to the working point of the amplifier and
to avoid the saturation of the amplifier.