IEEE Solid-State Circuits Magazine - Fall 2017 - 97

ZI

ISOURCE/SINK

ZV

Z1

+
I (0°)

Gain
-

Vout

Z2 I (180°)
Vout = I × (Z1 + Z2) × Gain
ETI

diac signals," IEEE Trans. Biomed. Circuits
Syst., vol. 7, no. 6, pp. 785-795, Dec. 2013.

ISOURCE

About the Authors

+

ZBIO

Gain

Vout

-
ZV
ZI

ISINK

Vout = I × ZBIO × Gain
Bio-Z

FIGURE 9: ETI versus Bio-Z measurements.

obtained by measuring the voltage
between two electrodes using current
source ISOURCE and ISINK. One of the purposes of measuring the ETI is to suppress the motion artifact as ETI highly
correlates to the electrode impedance
mismatch depicted in Figure 3(d).
In practice, the ETI and biopotential
signal are monitored simultaneously
and their correlation is extracted to
get an artifact-free signal through an
adaptive filtering [7]. The Bio-Z, on the
other hand, utilizes tetrapolar electrodes configuration (two for current
injection and two for voltage readout)
to mitigate the effects of the ETI by
picking up voltage signal across the
tissue only. It is worth noting that
the output impedance of the current
source and input impedance of the
amplifier must be sufficiently high
for Bio-Z measurement. Determining
the waveform of the injection current
is also important. For the purpose of
high-resolution Bio-Z measurements,
a sine wave [8] is preferred to a square
wave [7] at the cost of much more
power consumption. A reasonable
design tradeoff can be considered to
implement quantized sine wave-attenuating low-frequency harmonics with
low power dissipation [9].

Conclusions
When designing readout circuits for
physiological signal measurement,
one needs to understand that applications define the required signal
quality and the circuit architecture.
In addition, a clear understanding of

electrode interface is as important
as the circuit design since it is first
and an integral part of the readout
circuits. It is also necessary to be
aware of signal aggressors so that
they can be removed properly. The
readout circuits are part of the overall system; therefore, various challenges and issues can be addressed
in other parts of the system.

References

[1] J. G. Webster, Medical Instrumentation:
Application and Design, 2nd ed. Boston,
MA: Houghton Mifflin, 1992.
[2] Y. M. Chi, T. P. Jung, and G. Cauwenberghsi, "Dry-contact and noncontact biopotential electrodes: Methodological review,"
IEEE Rev. Biomed. Eng., vol. 3, no. 1, pp.
106-119, 2010.
[3] A. M. Van Rijn, A. Peper, and C. A. Grimbergen, "High-quality recording of bioelectric events: Part 1, interference reduction, theory, and practice," Med. Biol. Eng.
Comput., vol. 28, no. 5, pp. 389-397, 1990.
[4] M. J. Burke, and D. T. Gleeson, "A micropower dry-electrode ECG preamplifier,"
IEEE Trans. Biomed. Eng., vol. 47, no. 2, pp.
155-162, Feb. 2000.
[5] L. Yan, P. Harpe, M. Osawa, Y. Harada, K.
Tamiya, C. Van Hoof, and R. F. Yazicioglu, "A
680nA fully integrated implantable ECG-acquisition IC with analog feature extraction,"
in Proc. ISSCC Tech. Dig., 2014, pp. 418-419.
[6] R. F. Yazicioglu, P. Merken, R. Puers, and
C. Van Hoof, "A 60μW 60nV/√Hz readout
front-end for portable biopotential acquisition systems," IEEE J. Solid State Circuits,
vol. 41, no. 5, pp. 1100-1110, , May 2007.
[7] R. F. Yazicoglu, S. Kim, T. Torfs, H. Kim, and
C. Van Hoof, "A 30μW analog signal processor ASIC for portable biopotential signal
monitoring," IEEE J. Solid State Circuits, vol.
46, no. 1, pp. 209- 223, Jan. 2011.
[8] ] L. Yan, J. Bae, S. Lee, T. Roh, K. Song, and
H. J. Yoo, "A 3.9mW 25-electrode reconfigured sensor for wearable cardiac monitoring system," IEEE J. Solid State Circuits,
vol. 46, no. 1, pp. 353- 364, Jan. 2011.
[9] L. Yan, J. Pettine, S. Mitra, S. Kim, D. W.
Jee, H. Kim, M. Osawa, Y. Harada, K. Tamiya, C. Van Hoof, and R. F. Yazicioglu, "A
13μA analog signal processing IC for accurate recognition of multiple intra-car-

Long Yan (yanlong.ee@gmail.com)
received the B.S., M.S., and Ph.D.
degrees from the Korea Advanced
Institute of Science and Technology, in
2007, 2009, and 2011, respectively. In
2010, he was with the Massachusetts
Institute of Technology Microsystems
Technology Laboratory as a visiting
student, where he developed a lowpower EEG readout front-end. From
2011 to 2014, he was with IMEC, Belgium, as a senior scientist. His research
at IMEC focused on the development
of low-power mixed-signal circuits
for wearable and implantable applications. In December 2014, he joined
Samsung Electronics, Korea, where he
is now leading analog interface circuit
developments for nex-generation biosensors. He is a Senior Member of the
IEEE and serves on the Technical Program Committee of the International
Solid-State Circuits Conference.
Joonsung Bae (baej@kangwon
.ac.kr) received the B.S., M.S., and
Ph.D. degrees in electrical engineering
from the Korea Advanced Institute of
Science and Technology (KAIST), Daejeon, in 2007, 2009, and 2013, respectively. Since 2017, he has been with
the Department of Electrical and Electronics Engineering, Kangwon National
University, where he is an assistant
professor. From 2013 to 2014, he was
with the Memory Business of Samsung Electronics, Korea. In 2014, he
joined the Information and Electronics
Research Institute of KAIST as a postdoctoral researcher. Before joining
Kangwon National University, he was
an analog circuit designer with IMEC,
Belgium. His current research interests are energy-efficient mixed-signal
circuits and systems for the Internet
of Things, biomedical sensors, and
body area networks. He received the
Asian Solid-State Circuits Conference
Best Design Awards in 2011 and 2014
and the Global Internship Scholarship
of National Research Foundation of
Korea in 2012.

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