IEEE Solid-States Circuits Magazine - Summer 2023 - 49

biological cells and tissues, and it
plays a crucial role in understanding
the functioning of the human body.
It involves not only the measurements
of voltage changes, electric
currents, and bioimpedances but
also the manipulation of biological
tissues at different scales. The roots
of electrophysiology can be traced
back to the groundbreaking research
of Luigi Galvani, who discovered, in
1791, that the muscles of dead frogs
could be activated by the application
of electrical currents. This inspired
research into the concept of " bioelectricity "
and eventually led to the
development of instrumentation for
recording the small electrical currents
and potentials of tissue and
even individual cells.
After the invention of transistors
and ICs, the emerging analog circuit
design techniques were adopted for
the development of more advanced,
miniaturized, and implantable biomedical
interfaces. A highly impactful
early result was the invention of
the first implantable cardiac pacemaker,
in 1958 (by Ake Senning). In
the 1970s, this was greatly improved
by the introduction of IC sensing amplifiers,
digital logic, and noninvasive
electronic control [48]. In the same decade,
groundbreaking work on the use
of implantable microelectrodes for the
recording of brain biopotentials was
reported by Kensall Wise [49]. These
developments laid the foundations for
modern silicon neural probes.
Today, modern electrophysiology
techniques allow the accurate measurement
of biopotentials originating
from the heart, brain, nerves, and muscles.
In particular, wearable cardiac
monitoring has become increasingly
popular, especially for the long-term
monitoring of patients with cardiovascular
conditions. ICs and technology
scaling enable a broad range of biomedical
devices, including implants
for sensory prostheses (e.g., cochlear
and retinal implants), motor prostheses
(e.g., to control robotic arms), brain
pacemakers (i.e., deep brain stimulators),
glucose sensing, and insulin delivery,
among many others.
The invention of the transistor and the IC
and the ensuing technology scaling have
changed our world more than most inventions
in human history.
Many of these biomedical applications
require specialized readout
electronics to acquire biopotentials
with high signal quality. As illustrated
in Figure 8, low noise, high input
impedance, a high common-mode
rejection ratio, and a large differential
input range to avoid saturation
caused by motion artifacts [38]
are critical for reliable and accurate
wearable readout systems [50]. In addition,
very low power consumption
is required to achieve reasonable
battery life. Typically, a fully differential
high-input-impedance instrumentation
amplifier (IA) is used to
amplify biopotential signals. Since
the IA characteristics dominate the
(a)
5 µm
50 µm
100 µm
(b)
(c)
(d)
FIGURE 9: (a) A fully fabricated Neuropixels 2.0 CMOS probe, with details of the probe
(b) neck, (c) tip, and (d) electrodes [53].
Doubling Time: 6.3 ± 0.2 Years (n = 92)
1,000
100
500
10
50
1
5
Publication Date
FIGURE 10: The 2020 version of the Moore's law of neuroscience plot reported in [56].
IEEE SOLID-STATE CIRCUITS MAGAZINE
SUMMER 2023
49
Simultaneously Recorded Neurons
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IEEE Solid-States Circuits Magazine - Summer 2023

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