IEEE Solid-States Circuits Magazine - Fall 2023 - 38

with the IMD, a general principle is to
reduce the complexity and power consumption
of the IMD, often at the expense
of increased complexity in the
external data receiver, which is not subject
to the same constraints [72].
Far-field data communication offers
the advantages of greater data
transmission distance and higher data
bandwidth. However, conventional farfield
data communication methods
typically consume a relatively significant
portion of the IMD's power budget
compared to other circuit blocks in
the IMD [73]. Considering that the Tx
and Rx coils are already incorporated
for wireless powering, near-field data
communication can be considered
a more power-efficient approach for
IMDs [74], [75], [76], [77], [78]. Nonetheless,
the data rate of near-field
communication is limited by the carrier
frequency of the inductive link.
Therefore, designers need to carefully
select suitable data telemetry methods,
taking into account the practical
constraints of IMD design, including
power budget, device size, data bandwidth,
reliability, and more.
Conclusion and Future Work
IMDs play a crucial role in clinical applications
and neuroscience research.
The integration of emerging neural
interface modalities, such as optical
stimulation and simultaneous neural
recording, within IMDs holds immense
potential in unveiling novel insights
into the fundamental neural mechanisms.
This progress paves the way for
the development of promising therapies
for a wide range of neurological
disorders. Furthermore, advancements
in WPT and data telemetry significantly
enhance the practicality and relevance
of IMDs in both clinical applications
and behavioral neuroscience research.
This review provides an overview of the
background and recent advancements
in optical stimulation circuit designs,
neural recording AFE designs, and
wireless power and data transmission.
These advancements contribute to the
development of cutting-edge IMDs for
wireless optical neuromodulation and
neural recording.
38
FALL 2023
This review only highlights a fraction
of the vast potential that circuit
designers can bring to the field of IMDs.
One promising direction for further
advancement is the development of
closed-loop IMDs. Recent works have
introduced IMDs that enable closedloop
optical neuromodulation by incorporating
signal processing units
[79], [80]. Looking forward, designers
can explore implementing machine
learning-assisted intelligent processing
to further refine the energy efficiency,
accuracy, and safety of the closed-loop
optical neuromodulation. Another exciting
avenue is the integration of other
types of neural interface modalities,
such as electrochemical sensing. This
neural interface modality would require
exploration of AFE designs beyond voltage-based
recording. Furthermore, an
IMD capable of recording electrophysiology
and electrochemical signals while
performing neuromodulation would
provide new insights into neural communication
mechanisms. Finally, significant
efforts also can be dedicated
to enhancing the efficiency and safety
of existing WPT in IMDs. For example,
researchers have implemented ultrasonic-inductive
hybrid links that can
utilize the strengths of these two WPT
approaches [81], [82]. Therefore, continued
exploration and innovation in
circuit design and related areas will
undoubtedly shape the future of IMDs,
paving the way for groundbreaking discoveries
in neuroscience and improved
patient outcomes. The journey to fully
unlock the potential of IMDs and their
impact on clinical practice and neuroscience
research has just begun.
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