IEEE Solid-States Circuits Magazine - Spring 2020 - 44

103

RZ
ASK/OOK
FSK
Backscatter
UWB
PM
LSK

DR (Mb/s)

102

101

100

10-1

2004

2006

2008

2010 2012
Year

2014

2016

2018 2020

FIGURE 12: The trends in reported data rates over the last 15 years. RZ: return-to-zero;
ASK: amplitude-shift keying; OOK: on-off keying; FSK: frequency-shift keying; UWB: ultrawideband; PM: pulse modulation; LSK: load-shift keying.

and high data rates by transmitting
data using wideband pulses over
inductive links. Schormans et al.
recently presented a pulse-harmonic
modulation (PHM) approach, coined
short-range quality-factor modulation (SQuirM), that can support data
rates of 50 Mb/s while consuming
400 nW, resulting in an energy efficien-
cy of 8 pJ/b (picojoule/bit) [44]. The
-
need to achieve data rates beyond
10 Mb/s to accommodate a high channel count in modern neural interfaces
has motivated the use of far-field
radio-frequency (RF) links for data
transfer (often in combination with
inductive links for powering [45]-
[47]). In far-field systems, FCC-regulated ISM bands are often used,
including 433 MHz, 915 MHz, and
2.4 GHz. Impulse-radio ultrawideband
(UWB) communication has become
increasingly popular in the domain
of implantable devices, thanks to its
ability to support ultrahigh data rates
in excess of 50 Mb/s. Mirbozorgi
et. al. recently presented a UWB system working in the frequency band
between 3.1 and 7 GHz that is capable
of achieving data rates on the order
of 500 Mb/s while consuming only
3.5 mW, resulting in a high energy
efficiency of 7 pJ/b, comparable to
PHM in inductive links. Figure 12

44	

S P R I N G 2 0 2 0	

shows the trends in reported data
rates achieved by different modulation schemes.
RF links will likely be the dominant choice for future high-density
wireless neural implants. UWB, in
particular, is poised to become the
prevailing strategy to achieve energyefficient high-data rate to support
future high-density wireless neural
interfaces. Coupled with the design
of ultralow-power circuits and signal
processing, the design of robust and
energy-efficient links will support
further scaling and miniaturization
of future neural implants.

Conclusions
This tutorial presented a general
framework for bioelectronic platforms from a circuit perspective, in--
cluding all of the critical components
for the technology stack. In the future,
the use of bioelectronic systems with
complex control could usher in an era
of therapies that complement pharmaceutical methods.

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