IEEE Circuits and Systems Magazine - Q4 2020 - 1

Circuits
and Systems
IEEE

MAGAZINE

Volume 20, Number 4ââ Fourth Quarter 2020

Features

100 Years of Colpitts Oscillators: Ontology Review
of Common Oscillator Circuit Topologies
Mehdi Azadmehr, Igor Paprotny, and Luca Marchetti

The year 2018 marked 100 years since the introduction of a class of oscillatory circuits called Colpitts
oscillators. Few other electronic circuits have survived for such a long time and affected the electronic
technology as the Colpitts oscillator. Today, Colpitts oscillators are found in both communication systems and digital circuits as clock and frequency generators. In this paper, we provide a comprehensive
overview over the development of the Colpitts oscillator, from the simple vacuum tube oscillator patented by Colpitts in 1918, to state of the art MEMS oscillators operating at high GHz region in today's
modern electronics. We review different types of Colpitts oscillators, including single-ended, differential,
complementary, gm-boosted and introduce a timeline for the development of these circuits.

Printed in U.S.A.

Gabriel Gagnon-Turcotte, Guillaume Bilodeau, Olivier Tsiakaka, and Benoit Gosselin

The future of brain research lies in the application of new technologies drawing from the latest
developments in biology, physics and engineering to advance our understanding of how this
complex organ processes, integrates and transfers information. Among these, optogenetics is a
groundbreaking technology that allows using light to selectively activate neurons in the cortex of
transgenic animals, usually mice, to observe its effect in large biological networks. A new research
paradigm drawing from these advances consists of synchronizing optogenetic stimulation with
electrophysiology recordings, to close the loop and to regulate the neural microcircuits, or to
repair them. Such an approach holds promise to accelerate the development of new therapeutics
against brain diseases by enabling entirely new experimental research scenarios with freely
behaving animal -models. As a result, the development of advanced wireless microelectronic
implantable systems to elicit, ex--tract and process brain data in real time has become a source of
significant interest. This paper reviews the design challenges and the state-of-the-art technology
in this field. We present the design of a complete electro-optic device for preforming optogenetics and multichannel electrophysiology in a closed-loop (CL) system with live neurons. We cover
the design of the different CMOS integrated building blocks involved in this system to perform
photostimulation and multichannel neural recording in parallel. We describe advanced hardware
strategies to perform action potential (AP) detection, neural data compression and AP sorting in
real-time, over several parallel recording channels for enabling real-time CL neural control. Finally,
we present CL experimental results obtained in vivo with an electro-optic prototype.

Â©SHUTTERSTOCK/SDECORET

IEEE Circuits and Systems Magazine (ISSN 1531-636X)
(ICDMEN) is published quarterly by the Institute of Electrical and Electronics Engineers, Inc. Headquarters: 3
Park Avenue, 17th Floor, New York, NY, 10016-5997 USA.
Responsibility for the contents rests upon the authors and
not upon the IEEE, the Society, or its members. IEEE Service
Center (for orders, subscriptions, address changes): 445
Hoes Lane, Piscataway, NJ 08854 USA. Telephone: +1 732
981 0060, +1 800 678 4333. Individual copies: IEEE members
US$20.00 (first copy only), nonmembers US$183 per copy;
US$7.00 per member per year (included in Society fee)
for each member of the IEEE Circuits and Systems Society. Subscription rates available upon request. Copyright
and Reprint Permission: Abstracting is permitted with
credit to the source. Libraries are permitted to photocopy
beyond the limits of the U.S. Copyright law for private use
of patrons: 1) those post-1977 articles that carry a code
at the bottom of the first page, provided the per-copy fee
indicated in the code is paid through the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923; and
2) pre-1978 articles without fee. For other copying, reprint,
or republication permission, write to: Copyrights and
Permissions Department, IEEE Service Center, 445 Hoes
Lane, Piscataway, NJ 08854 USA. Copyright Â© 2020 by the
Institute of Electrical and Electronics Engineers, Inc. All
rights reserved. Periodicals postage paid at New York, NY,
and at additional mailing offices. Postmaster: Send address
changes to IEEE Circuits and Systems Magazine, IEEE Operations Center, 445 Hoes Lane, Piscataway, NJ, 08854 USA.

Smart Autonomous Electro-Optic Platforms
Enabling Innovative Brain Therapies

Broadband Highly Efficient Doherty Power Amplifiers
Xin Yu Zhou, Wing Shing Chan, Shichang Chen, and Wen Jie Feng

Modern wireless communication systems with large bandwidth and high peak-to-average power
ratios (PAPRs) have been and will continue to be in wide demand. This puts a strain on the
transmitter, which has to operate with its average power in the output back-off (OBO) region.
The Doherty power amplifier (Doherty PA) was invented in 1936 as an alternative to the highly
inefficient linear amplifiers used in radio transmitters. The Doherty PA has recently undergone a
renaissance, becoming the PA architecture of choice for mobile radio base stations. The additional
efficiency peak at the OBO point makes it ideal for high PAPR signals. However, the main drawback of conventional Doherty PAs is its narrow bandwidth, which significantly limits its applicability.
Recently, broadband Doherty PAs have been realized using a technique called " post-matching "
and have attracted much attention. In this paper, the operating principles of conventional and
broadband Doherty PAs are reviewed, followed by an analysis of recently reported prototypes,
current technical challenges, and application in 5G wireless communication systems. As a comparison, process technologies for the implementation of Doherty PAs are also surveyed.

Digital Object Identifier 10.1109/MCAS.2020.3026791

FOURTH QUARTER 2020

IEEE CIRCUITS AND SYSTEMS MAGAZINE

IEEE Circuits and Systems Magazine - Q4 2020

Table of Contents for the Digital Edition of IEEE Circuits and Systems Magazine - Q4 2020