IEEE Circuits and Systems Magazine - Q3 2022 - 28

module (i.e., blue tooth module LM07, Liangming). The
two boards are inter-connected via rigid vertical wires.
The weight of the WER is 17 g. Taking the ceramic case
into account, the diameter and thickness of the WER are
26 mm and 10 mm, respectively.
The IVNS can also be implemented with two discrete
component boards: a pulse generator board and a wireless
power receiver and data telemetry board. The pulse
generator board includes an ultra-low power MCU (i.e.,
similar to the one in the WER), a pulse generator combined
with a DC impedance extractor, and a temperature
sensor (i.e., SMT172, Smartec). The wireless power
receiver and data telemetry board includes a wireless
power receiver and a data telemetry module (i.e., similar
to the one in the WER). The detailed design of the wireless
power receiver is presented in Section VIII. Fig. 5
shows the two boards of the IVNS. The weight of the
IVNS is 24 g. Taking the biocompatible ceramic case into
account, the diameter and thickness of the IVNS are
30 mm and 12 mm, respectively.
V. The 4-Channel Preamplifier
The 4-channel preamplifier records and amplifies EEG signals
induced on the scalp, which are continuous lower-frequency
signals with amplitudes around a few hundred µV
[21], [22]. The ETI as seen by the front-end of the 4-channel
preamplifier can be modeled as a capacitance (150 pF to
1.5 nF, depending on the electrode area and surface roughness)
for small voltages [23]. In addition, the electrode DC
offset (EDO) at the ETI depends on the electrodes used
and the properties of the electrolyte (the skin) but is typically
between 1 and 10 mV and can be up to 50-300 mV
[24]. Moreover, the 4-channel preamplifier might record
large amounts of power-line interference (PLI) at 50/60 Hz.
Therefore, both the EDO and the PLI should be properly
filtered out at the preamplifier. Thanks to the rechargeable
battery and the wireless data telemetry, the PLI in
the WER is kept small since there is neither galvanic nor
capacitive coupling from the mains to the WER.
Fig. 6 shows a single channel of the 4-channel preamFigure
3. App of the HybridVNS.
Scalp EEG Recording Board
plifier. Its input stage is a capacitively coupled instrumentation
amplifier (CCIA), in which the EDO can be
blocked by input coupling capacitors (C1 and C2). To constrain
1/f noise and drift, the core of the CCIA exploits
such an operational amplifier (OPAMP; i.e., TLVx333, TI)
that offers near-flat 1/f noise and low offset voltage due
Ceramic Case
Pulse Generator Board
Ceramic Case
Cabled Charge Management
and Data Telemetry Board
Wireless Power Receiver
and Data Telemetry Board
Figure 4. The WER and its circuit boards.
28
IEEE CIRCUITS AND SYSTEMS MAGAZINE
Figure 5. The IVNS and its circuit boards.
THIRD QUARTER 2022

IEEE Circuits and Systems Magazine - Q3 2022

Table of Contents for the Digital Edition of IEEE Circuits and Systems Magazine - Q3 2022

Contents
IEEE Circuits and Systems Magazine - Q3 2022 - Cover1
IEEE Circuits and Systems Magazine - Q3 2022 - Cover2
IEEE Circuits and Systems Magazine - Q3 2022 - Contents
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