2021年7月IEEE固态电路期刊：创新设计与应用论文精选

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《JSSC_202107》是IEEE固态电路期刊的一期，专注于每月发布的关于固体电路的广泛研究，特别强调集成电路的晶体管级设计。该期刊的内容涵盖了许多尖端的电路技术，这期特别关注以下几个重要主题： 1. 无晶振的GFSK调制BLE（蓝牙低功耗）数据包中的时钟恢复技术：论文由X. Chen、A. Alghaihab等人提出，他们设计了一种创新的系统，能在接收GFSK调制的BLE数据包时实现高精度的时钟恢复，这对于无线通信系统的高效工作至关重要。 2. 基于28纳米CMOS的145 GHz FMCW雷达系统及电路分析：A. Visweswaran等人分享了他们在毫米波雷达领域的研究成果，包括系统架构、电路设计以及性能验证，这对于无线传感和雷达应用具有重要意义。 3. 基带匹配电阻噪声取消接收器：A. N. Bhat等人介绍了一种仅采用三阶段运算放大器的接收器设计，旨在提高在宽频带和高增益输入信号下的信噪比（In-Band IIP3），适合于物联网应用中的信号处理。 4. 2.4 GHz高度选择性的IoT接收前端：论文讨论了如何通过优化功率管理的本地噪声温度放大器（LNTA）、频率分频器以及基带模拟滤波器来增强物联网设备的接收性能。 5. 直接RF发射器的时间近似滤波器：S. Su和M. S.-W. Chen设计了一种用于简化直接RF发射器设计的技术，可能涉及射频信号的精确时间处理和优化。 6. 四象限Class-G复数域多级数字功率放大器：S.-C. Hung、S.-W. Yoo和S.-M. Yoo共同研发的这一新型数字功率放大器技术，对提升无线通信系统的效率和性能有着显著贡献。 7. 低温环境下的宽带低噪声放大器：Y. Peng、A. Rufino和E. Charbon合作的论文展示了针对量子应用的低温条件下，如何实现低于1分贝噪声系数的宽带低噪声放大器，这是量子计算和通信领域的关键组件。 8. 结构工程学的前沿研究：最后，本期还包括了有关电路结构和设计的创新工作，这些可能涉及到新材料、新技术在固态电路中的集成与优化。《JSSC_202107》提供了一个平台，让研究人员展示他们在高频、高速、低功耗和量子技术等领域的最新进展，这些成果将推动整个电子和通信行业的进步。

1974 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 56, NO. 7, JULY 2021

[11] F. Maksimovic et al., “A crystal-free single-chip micro mote with

integrated 802.15.4 compatible transceiver, sub-mW BLE compatible

beacon transmitter, and cortex m0,” in Proc. Symp. VLSI Circuits,

Jun. 2019, pp. C88–C89.

[12] A. Alghaihab, X. Chen, Y. Shi, D. S. Truesdell, B. H. Calhoun, and

D. D. Wentzloff, “30.7 A crystal-less BLE transmitter with -86 dBm

freq μ ency-hopping back-channel WRX and over-the-air clock recovery

from a GFSK-modulated BLE packet,” in IEEE Int. Solid-State Circuits

Conf. (ISSCC) Dig. Tech. Papers, San Francisco, CA, USA, Feb. 2020,

pp. 472–474, doi: 10.1109/ISSCC19947.2020.9062935.

[13] A. Alghaihab, Y. Shi, J. Breiholz, H.-S. Kim, B. H. Calhoun, and

D. D. Wentzloff, “Enhanced interference rejection Bluetooth low-energy

back-channel receiver with LO frequency hopping,” IEEE J. Solid-State

Circuits, vol. 54, no. 7, pp. 2019–2027, Jul. 2019.

[14] X. Chen, “Analysis and design of energy efﬁcient frequency synthesizers

for wireless integrated systems,” Ph.D. dissertation, Dept. Elect. Eng.

Comput. Sci., Univ. Michigan, Ann Arbor, MI, USA, 2019.

[15] A. A. Abidi, “Phase noise and jitter in CMOS ring oscillators,” IEEE

J. Solid-State Circuits, vol. 41, no. 8, pp. 1803–1816, Aug. 2006.

[16] X. Chen, H.-S. Kim, and D. D. Wentzloff, “An analysis of phase noise

requirements for ultra-low-power FSK radios,” in Proc. IEEE Radio

Freq. Integr. Circuits Symp. (RFIC), Honolulu, HI, USA, Jun. 2017,

pp. 37–40.

[17] X. Chen et al., “Analysis and design of an ultra-low-power Bluetooth

low-energy transmitter with ring oscillator-based ADPLL and 4× fre-

quency edge combiner,” IEEE J. Solid-State Circuits, vol. 54, no. 5,

pp. 1339–1350, May 2019.

[18] N. Da Dalt and A. Sheikholeslami, Understanding Jitter and Phase

Noise: A Circuits and Systems Perspective. Cambridge, U.K.: Cambridge

Univ. Press, 2018.

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“A 2.4 GHz reference-less receiver for 1 Mbps QPSK demodulation,”

IEEE Trans. Circuits Syst. I, Reg. Papers, vol. 59, no. 3, pp. 505–514,

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[20] Bluetooth, ‘Core System Package [Low Energy Controller],’ in Bluetooth

Core Speciﬁcation V 5.0. Accessed: May 2020. [Online]. Available:

https://www.bluetooth.com/

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phones,” IEEE J. Solid-State Circuits, vol. 40, no. 12, pp. 2469–2482,

Dec. 2005, doi: 10.1109/JSSC.2005.857417.

[22] N. H. Sabah, Electric Circuits and Signals. Boca Raton, FL, USA:

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LC oscillator phase noise,” IEEE J. Solid-State Circuits, vol. 36, no. 12,

pp. 1921–1930, Dec. 2001, doi: 10.1109/4.972142.

Xing Chen (Member, IEEE) received the B.S.

degree from the Beijing Institute of Technology,

Beijing, China, in 2013, and the M.S. and Ph.D.

degrees from the University of Michigan, Ann

Arbor, MI, USA, in 2015 and 2019, respectively.

In 2019, he joined Qualcomm, San Diego, CA,

USA, as a Senior Engineer, where he is developing

frequency synthesizers and wireless transceivers for

5G applications. He also held internship positions at

Qualcomm, in 2018; Everactive, Inc., Ann Arbor,

in 2017; and Carnegie Mellon University, Pitts-

burgh, PA, USA, in 2014. His research interests include millimeter-wave/

RFIC design, frequency synthesizers, wireless transceivers, and energy-

efﬁcient wireless integrated systems.

Abdullah Alghaihab (Member, IEEE) received the

B.S. degree in electrical engineering from King Saud

University, Riyadh, Saudi Arabia, in 2013, and the

M.S. and Ph.D. degrees from the University of

Michigan, Ann Arbor, MI, USA, in 2016 and 2020,

respectively.

He is currently an Assistant Professor with King

Saud University. His research interests include

RF/mixed-signal IC design for wireless communi-

cation and low-power wireless transceivers circuit

design and self-powered system on chip design for

the internet of things-based applications.

Yao Shi (Member, IEEE) received the B.S. degree

in electronic and information engineering from

Zhejiang University, Zhejiang, China, in 2013, and

the M.S. and Ph.D. degrees in electrical engineering

from the University of Michigan, Ann Arbor, MI,

USA, in 2016 and 2018, respectively.

From 2018 to 2020, he was a Design Engineer

with the MediaTek Inc., San Jose, CA, USA, devel-

oping radio frequency (RF) and millimeter-wave

(mm-wave) integrated circuit for WiFi and 5G wire-

less transceivers. Since 2020, he has been with

Apple Inc., Cupertino, CA, working on advanced display technology, system

architecture, and novel algorithm for future products.

Daniel S. Truesdell (Member, IEEE) received

the B.S. degree in electrical engineering from the

University of Central Florida, Orlando, FL, USA,

in 2016. He is currently pursuing the Ph.D. degree

in electrical engineering with the University of

Virginia, Charlottesville, VA, USA.

His current research interests include energy-

efﬁcient mixed-signal circuit design, on-chip

oscillators and sensors, energy-harvesting and

performance-scalable systems, and low-power

digital circuit techniques.

Benton H. Calhoun (Senior Member, IEEE)

received the B.S. degree from the University of

Virginia, Charlottesville, VA, USA, in 2000, and

the M.S. and Ph.D. degrees in electrical engineer-

ing from the Massachusetts Institute of Technol-

ogy, Cambridge, MA, USA, in 2002 and 2006,

respectively.

He is currently a Professor with the Electrical

and Computer Engineering Department, University

of Virginia. He is also the Campus Director and

the Technical Thrust Leader with the NSF Nanosys-

tems Engineering Research Center for Advanced Self-Powered Systems of

Integrated Sensors and Technologies (ASSIST) Alexandria, VA. He has

coauthored the Sub-Threshold Design for Ultralow-Power Systems (Springer,

2006) and authored the Design Principles for Digital CMOS Integrated Circuit

Design (NTS Press, 2012). His research interests include body area sensor

nodes (BSNs), wireless sensor networks (WSNs), low-power digital circuit

design, subthreshold digital circuits, subthreshold ﬁeld-programmable gate

arrays (FPGAs), static random access memory (SRAM) design for end-

of-the-roadmap silicon, power delivery circuits and architectures, variation

tolerant circuit design methodologies, and low-energy electronics for medical

applications.

David D. Wentzloff (Senior Member, IEEE)

received the B.S.E. degree in electrical engineer-

ing from the University of Michigan, Ann Arbor,

MI, USA, in 1999, and the S.M. and Ph.D.

degrees from the Massachusetts Institute of Tech-

nology, Cambridge, MA, USA, in 2002 and 2007,

respectively.

Since August 2007, he has been with the Univer-

sity of Michigan, where he is currently an Associate

Professor of electrical engineering and computer

science. In 2012, he co-founded PsiKick, a fab-

less semiconductor company developing ultralow-power wireless SoCs. His

research focuses on RF integrated circuits, with an emphasis on ultralow-

power design.

Dr. Wentzloff was a recipient of the 2009 DARPA Young Faculty

Award, the 2009–2010 Eta Kappa Nu Professor of the Year Award,

the 2011 DAC/ISSCC Student Design Contest Award, the 2012 IEEE Sub-

threshold Microelectronics Conference Best Paper Award, the 2012 NSF

CAREER Award, the 2014 ISSCC Outstanding Forum Presenter Award, the

2014–2015 Eta Kappa Nu ECE Professor of the Year Award, the 2014–2015

EECS Outstanding Achievement Award, and the 2015 Joel and Ruth Spira

Excellence in Teaching Award. He has served on the technical program

committee for ICUWB 2008–2010, ISLPED 2011–2015, S3S 2013–2014,

RFIC 2013–2020, and ISSCC 2020, and as a Guest Editor for the IEEE

T-MTT, the IEEE Communications Magazine,andtheElsevier Journal of

Signal Processing: Image Communication. He is a Senior Member of the IEEE

Circuits and Systems Society, the IEEE Microwave Theory and Techniques

Society, the IEEE Solid-State Circuits Society, and the Tau Beta Pi.

IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 56, NO. 7, JULY 2021 1975

A 28-nm-CMOS Based 145-GHz FMCW Radar:

System, Circuits, and Characterization

Akshay Visweswaran , Member, IEEE, Kristof Vaesen, Member, IEEE, Miguel Glassee, Member, IEEE,

Anirudh Kankuppe

, Member, IEEE, Siddhartha Sinha , Member, IEEE, Claude Desset, Member IEEE,

Thomas Gielen

, André Bourdoux, Senior Member, IEEE, and Piet Wambacq , Member, IEEE

Abstract—This article presents frequency-modulated-

continuous-wave (FMCW) radars developed for the detection

of vital signs and gestures using two generations of 145-GHz

transceivers (TRXs) integrated in 28-nm bulk CMOS. The

performance and limitations of high-frequency radars are

quantiﬁed with a system-level study, and the design and

performance of individual circuit blocks are presented in detail.

A 145-GHz center frequency and radar operation over an

RF bandwidth of 10 GHz yield a displacement responsivity

of 2π rad/mm and a windowed range resolution of 30 mm,

respectively. Radar operation over a 0.1–7 m range is enabled

by an effective-isotropic radiated power of 11.5 dBm and a noise

ﬁgure of 8 dB. The ICs feature frequency multiplication by 9 in

the transmit and receive paths, sub-arrayed dipole antennas,

and neutralization of TX–RX leakage via delay control. A single

TRX dissipates 500 mW from a 0.9-/1.8-V drive. The use of

fast chirps (5–30-μs) mitigates the effect of 1/ f -noise at the

intermediate frequency (IF). Extensive characterization results

showcase state-of-the-art performance of the TRXs, while

the code-domain multiple-input and multiple-output (MIMO)

radars (1×4and4× 4) built with them demonstrate vital-sign

and gesture detections.

Index Terms— D-band (110–170 GHz), frequency modulated

continuous wave (FMCW), gesture recognition, leakage neutral-

ization, link budget, on-chip antennas, radar.

I. INTRODUCTION

OMPACT high-resolution millimeter-wave radars,

resilient to ﬂuctuations in ambient temperature and

light, are advancing the role of wireless systems in social

infrastructure. Radars in the 30–300-GHz range that have

catered historically to niche requirements in telemetry,

spectroscopy, and military reconnaissance [1] are ﬁnding

application in daily lives. These include automotive sensing,

imaging and security control in public spaces, and detection

of people and vital signs over short ranges [2]–[11]. Gesture

recognition for contactless man–machine interaction is an

exciting application of high-resolution radars ready to foray

into the mass market of smart, portable devices. Enabled

Manuscript received July 2, 2020; revised September 16, 2020 and

October 30, 2020; accepted November 24, 2020. Date of publication Janu-

ary 6, 2021; date of current version June 29, 2021. This article was approved

by Associate Editor Payam Heydari. This work was supported in part by

Panasonic, Japan, and in part by the European Commission’s Horizon 2020

under Grant 783119. (Corresponding author: Akshay Visweswaran.)

The authors are with imec, 3001 Leuven, Belgium (e-mail:

akshay.visweswaran@imec.be).

Color versions of one or more ﬁgures in this article are available at

https://doi.org/10.1109/JSSC.2020.3041153.

Digital Object Identiﬁer 10.1109/JSSC.2020.3041153

by transistors that offer transit-frequencies beyond 350 GHz,

broad bandwidth and high ﬁdelity outline the next milestones

of integrated radar technology.

Frequencies in the vicinity of 150 GHz favor broadband

radars as mm-scale resolutions can be obtained with fractional

bandwidths below 10%. The design is, therefore, amenable

to power-efﬁcient RF techniques involving tuned circuits.

High-frequency carriers increase the angular resolution for a

given form factor and the displacement responsivity expressed

as phase rotation/displacement. They also facilitate compact

radars with antennas on the chip. From a system perspective,

correlation in frequency-modulated-continuous-wave (FMCW)

radars results in bandwidth compression at the intermediate

frequency (IF) [12]. This makes FM a low-complexity and

power-efﬁcient approach for broadband-RF performance.

This article details radar systems for vital-sign and gesture

detections developed with two generations of 145-GHz

FMCW-radar transceivers (TRXs) integrated in 28-nm bulk

CMOS. The ICs include a single-input-single-output (SISO)

TRX with on-chip antennas [10] and its adaptation as a

dual-transmitter (dual-TX) single-receiver (single-RX) chipset

for tiling arrayed systems. A TRX bandwidth of 13 GHz

and a 145-GHz center frequency yield a minimum range

resolution of 11 mm and a displacement responsivity of

2π-rad/mm, respectively. These performance metrics increase

the discrimination capabilities for ﬁne motions compared with

low-frequency radars while enabling smaller form factors. The

TRXs deliver 11.5 dBm of effective-isotropic radiated power

(EIRP), over a broad 3-dB bandwidth of 127–154 GHz. This

ensures the transmission of chirps with a constant amplitude

in the operating band. Integrated antennas and the LNA are

co-optimized for low-noise operation (8-dB noise ﬁgure), and

with 60 dB of programmable gain at IF, the TRXs also lend

themselves to short-range automotive sensing. The integrated

TRXs feature phase control for code-domain multiple-input

and multiple-output (MIMO) operation, TX-to-RX leakage

neutralization, the use of fast chirps (5–30 μs) to circumvent

1/ f -noise at IF, and a duty-cycled-FM transmission mode

for low-power operation. Complete MIMO-radar (1×4and

4×4) implementations using linear-FM chirps from the

sub-sampling PLL of [13] and an off-chip evaluation platform

are also showcased in this article.

Section II describes the performance and limitations of high-

frequency MIMO radars and the neutralization of TX–RX

leakage via delay control. The design of individual TRX

See https://www.ieee.org/publications/rights/index.html for more information.

1976 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 56, NO. 7, JULY 2021

Fig. 1. Simpliﬁed block diagram of the implemented radar system.

blocks and the on-chip antennas are detailed in Section III.

Section IV presents extensive characterization results of the

28-nm-CMOS TRXs and MIMO radars for the gesture and

vital-sign detection built using them. This work is summarized

in Section V.

II. FMCW R

ADAR SYSTEM

In linearly chirped FMCW radars, the correlation of

reﬂected and reference RF signals yields an IF tone pro-

portional to the time of ﬂight over the target distance.

System-level analysis of broadband MIMO FMCW radars

and visual interpretation of the design space in this section

provide a comprehensive summary of the 145-GHz system

showcased here and the underlying tradeoffs and effects that

shape performance.

A. Overview of the Integrated Transceivers

A simpliﬁed block diagram of the 145-GHz radar TRX is

shown in Fig. 1. It has a 3-dB RF bandwidth of 138–151 GHz.

An external chirp signal centered at 16.1 GHz is upconverted

to 145 GHz via a cascade of two harmonic frequency triplers

in the RX and TX. In the radar context, broadband FM

components resulting from non-linearities demonstrate center

frequencies and modulation indices that are scaled by a

factor of the corresponding harmonic coefﬁcient. Therefore,

while the bandwidth increases, the modulating waveform (i.e.,

the chirp function and its repetition interval) remains unal-

tered [14]. Despite operation at ∼ f

/2, thin metallization and

substrate losses affecting passives, and stringent density rules,

the TX EIRP is 11.5 dBm. The RX achieves a noise ﬁgure and

maximum conversion gain of 8 and 87 dB, respectively.

The radar operates over a 0.1–7-m range using fast chirps

of ∼5–30-μs duration (T

). The beat frequencies at IF ﬁt

between the 400-kHz and 15-MHz bandpass corners designed

for 40-dB/decade high-pass and 120-dB/decade low-pass

roll-offs, respectively. Low-pass ﬁltering suppresses noise

and aliasing above half the ADC sampling rate, f

s_ADC

of 80 MHz. The Nyquist-rate sampling yields a maximum

range of f

s_ADC

· c · T

/(4 · f

) m. High-pass ﬁltering, on

the other hand, attenuates the strong IF beat resulting from

TX–RX leakage. Apart from the time of ﬂight in the leakage

path, group delays of the PA and LNA shift this beat into the

vicinity of the RX passband, which saturates the high-gain

RX. This is overcome by delaying the 16.1-GHz RX chirp

on-chip. Section II-E shows that delay compensation can

eliminate the leakage beat and its phase noise (PN) entirely.

Fig. 2. IC micrographs of (a) SISO TRX [10] and (b) the single-RX and

dual-TX chipset, integrated in 28-nm bulk CMOS.

Above 100 GHz, in-package antennas (using advanced

technologies, such as FO-WLP and eWLB) and integrated

antennas can enable efﬁcient, broadband radiation of power

generated on the chip. The optimal choice is driven by an

application-based survey of performance, cost, complexity, and

yield. This work explores sub-arrayed dipoles on the chip

that mitigates deleterious substrate modes and radiates at 62%

efﬁciency. The radar ﬁelds of view are 100

◦

and 80

◦

in the

E-andH-planes, respectively.

Micrographs of the SISO TRX and its adaptation as a dual-

TX, single-RX chipset for tiling arrayed radars are shown

in Fig. 2(a) and (b), respectively. The RX in both versions is

identical. In the SISO TRX, spatial power combining results

from individual PA drive of the antenna sub-elements. For

layout compactness in the dual-TX chip, a single PA drives

the dipole sub-elements. The TRXs and on-chip antennas are

presented in Section III along with detailed block diagrams.

MIMO conﬁgurations typically entail antenna spacings of

multiples of λ

/2 (i.e., 1.1 mm at 145 GHz), depending on the

number of TX/RX elements. An additional physical separation

is often kept between TX- and RX-element clusters to mini-

mize crosstalk. Therefore, with an integrated-antenna solution,

a multi-chip approach utilizing less silicon area than a fully

integrated MIMO radar proves to be cost-efﬁcient. Coherent

detection subsequently necessitates a central chirp distribution

network that stems from an FM source external to individual

TX/RX elements in the array. To circumvent the distribution of

mm-wave signals, a linear chirp centered at 16.1 GHz from the

sub-sampling PLL developed for this work [13] is distributed

to multiple TRX chips on a PCB. MIMO radars implemented

with the ICs of Fig. 2 are detailed in Section II-D.

B. Link Analysis: Overcoming Negative SNR

The link budget for the gesture and heartbeat detection

is presented in this section. We would like to notify the

reader at the outset that numerous variables quantify the

system parameters of Table I. Although they are introduced

in the text when ﬁrst referred to, all variables and their units

are listed alphabetically in Table II for easy referencing at

any point.

The transmit power, P

, at 145 GHz is limited by the

technology, and the IF bandwidth is determined by the ADC

sampling rate. Table I considers a maximum transmit power

of 10 dBm per TX, antenna gains of 2 dBi, and an 80-MHz

sampling rate. The RX noise ﬁgure is 8 dB, while 10 GHz of

RF bandwidth yields a windowed range resolution of 27 mm

[see (3)]. The 145-GHz carrier frequency yields a displacement

responsivity of 2π rad/mm [see (4)]. The upper cutoff at IF

1978 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 56, NO. 7, JULY 2021

is 15 MHz [see (11)], leaving a margin for ﬁltering aliases

and noise above f

s_ADC

/2 [see (14): OSF > 5)]. More than

45-dB suppression is achieved at 40 MHz via the sixth-order

low-pass ﬁltering on-chip. The chirp duration is calculated

for objects at maximum range, R

max

[see (1)], to map to a

maximum IF, f

IF_max

, of 15 MHz via [see (9a)]. The requisite

fast chirps of 5–30-μs duration circumvent SNR degradation

due to ﬂicker noise due to the relatively high IF range [see

(11)]. The sawtooth modulation comprises the chirp duration,

, and the return time, T

[see (10)]. Additional dead time,

, may be included between chirps to aid PLL settling; it

is assumed to be zero here. Fast modulation also increases

the maximum unambiguous velocity, v

amb

[see (9b)], and the

separation at IF is seen between targets of varying radar-cross

sections (RCSs) in proximity.

The link analysis reveals a signiﬁcant loss in power

attributed to pathloss and an RCS of −40 dBsm [see (6)].

Movement of the thoracic chest induced by heart-

beats [15]–[17] is characterized in-house using a commercial,

79-GHz radar [18]. The RCS varies from −37 to −40 dBsm.

The RCS of a hand characterized at 60–90 GHz ranges

from −20 to −45 dBsm [19]. These match our estimates

of −38 to −42 dBsm. The representative value of −40 dBsm

in Table I is nearly ﬁve and four orders of magnitude lower

than automobiles and people, respectively [20], [21], which

is something that highlights the detection challenge.

Despite the compression of the noise bandwidth at IF

[see (7)], both scenarios encounter negative SNRs [see (8)].

Array and signal-processing gains [see (13) and (19)–(22)]

improve SNR after the ADC and are an integral part of

detection [see (23)]. They are explained in Appendix A. The

range-processing gain simpliﬁes to R

max

/(2 · δ

) when (9a)

is satisﬁed, and it is assumed that  f

-f

IF_max

≈ f

The ﬁner the range resolution (δ

), the better the SNR

per range bin is. In this work, the Blackman–Harris win-

dowing (sidelobe suppression >60 dB) is applied to the

range-processing FFT step, which enables target discrimina-

tion amid the clutter. A windowed DFT degrades the range res-

olution and SNR by a factor determined by the ﬁlter type [22].

Here, a windowing factor of 1.8 increases the resolution to

27 mm [see (3)] and introduces a ∼3-dB SNR degradation

[see (15)].

When the chirp duration is viewed in terms of [see

(1.09b)], the Doppler processing gain [see (19)] simpliﬁes

to (v

amb

res

), assuming T

+ T

≈ T

.However,inthe

heartbeat scenario in Table I, we employ digital ﬁltering (refer

to Appendix A for details) after the ﬁrst FFT, which dominates

the minimum processing time [see (25a)] required to meet a

viable-SNR threshold of 10 dB [see (24)]. Micromotions, such

as heartbeats and respiration of a static person, which do not

shift the range bin, result in a phase variation at IF determined

by the displacement responsivity [see (3)]. A motion of half

a wavelength (i.e., 1 mm) corresponds to a two-way phase

rotation of 360

◦

. The motion is typically detected as a change

in phase at IF in the range bin corresponding to the target

location, using successive Doppler FFTs and observing the

change in the argument of the complex FFT value in the

ﬁrst/dc Doppler bin. Gesture recognition using R-D maps

Fig. 3. Application space of the 145-GHz radar, parameterized by TX power,

range, minimum processing time, and chirp duration, for 15 MHz of f

10 GHz of  f

, and a target SNR of 10 dB.

and machine learning is explained in Section II-G. Radar

measurements are shown in Section IV.

C. Application Space and Limitations at 145 GHz

The detection of gestures and vital signs with 10-dB SNR

at distances of 1 m and 7 m, respectively, lies on diametric

ends of the design space parameterized by transmit-power

per TX, radar range, and minimum processing time (see

Fig. 3). The heartbeat detection with 10-dBm P

entails a

minimum processing time of 60 ms, while the gestures with

-10 dBm of P

require 3.6 ms. For radar to efﬁciently ﬁt

multiple scenarios, it requires: 1) ﬂexibility in T

to operate

over a constant IF bandwidth

[grey scale in Fig. 3, see

(11)] and 2) ﬂexibility in the output power. The ﬁrst require-

ment is met with the PLL of [13]. The latter is, however,

impeded by the diminishing back-off efﬁciency of power

ampliﬁers (PAs) at 145 GHz. State-of-the-art SiGe-BiCMOS

and FinFET-CMOS PAs achieve power-added efﬁciencies of

∼13% at saturated output power (P

sat

) levels of 15 and

18 dBm, respectively [23]–[25]. The 28-nm CMOS PA devel-

oped here delivers 7 dBm at 7% PAE. The desired radar

operation at peak efﬁciency, even at low output power levels,

is enabled by duty-cycled FM transmission (see Fig. 1), where

the TRX is switched

OFF between the chirps or a set of

chirps. It should be noted that, irrespective of waveform type,

the actual observation time determines the Doppler resolution.

While short- and mid-range applications at high frequen-

cies beneﬁt from improved ﬁdelity, broadband operation, and

small form factors, the detection of larger objects, people,

and vehicles over longer ranges encounters limitations in

SNR and velocity tracking. For a ﬁxed ﬁeld of view (i.e.,

antenna directivity) and P

(10 dBm here), the range of

operation increases with the array gain. Fig. 4(a) shows that

a four-element virtual array can detect larger targets (e.g.,

persons with an RCS of 5 dBsm) over nearly 47 m with

10-dB SNR. Larger ranges require a higher IF bandwidth,

Depending on complexity and needs, a ﬂexible IF band or a combination

of programmable chirp duration and IF band may also be used.

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2021年7月IEEE固态电路期刊：创新设计与应用论文精选

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