A Terahertz FMCW Comb Radar in 65nm CMOS with 100GHz … · © 2020 IEEE 4.8: A Terahertz FMCW Comb Radar in 65nm CMOS with 100GHz Bandwidth International Solid-State Circuits Conference

4.8: A Terahertz FMCW Comb Radar in 65nm CMOS with 100GHz Bandwidth© 2020 IEEE International Solid-State Circuits Conference 1 of 42

A Terahertz FMCW Comb Radar in

65nm CMOS with 100GHz Bandwidth

Xiang Yi1, Cheng Wang1, Muting Lu1, Jinchen Wang1,

Jesus Grajal1,2, and Ruonan Han1

1Massachusetts Institute of Technology, Cambridge, MA, USA2Universidad Politécnica de Madrid, Madrid, Spain


Outline

• Introduction

• Comb Radar

• Circuit Implementations

• Measurement Results

• Conclusion


Outline

• Introduction

• Comb Radar



• Conclusion


Wideband FMCW Radar Applications

[atap.google.com/soli]

Non-Ionizing/Destructive Imaging

• High resolution detection

∆𝑅 =𝑐

2 ∙ 𝐵𝑊 [Sheen, TMTT 2001]

[Mostajeran, TMTT 2019]

Localization

Recognition

• High resolution imaging

Security Imaging

Range Resolution

[humatics.com]


Defects

Material

D

BWFMCW

ΔR

ΔCR

R

Wideband THz FMCW Radar Example

• SAR 3D imaging

• Cross-range resolution ΔCR

– Relies on synthetic aperture D

– Mm resolution is readily available (e.g. R=3D, ΔCR=1.5mm)

• Range resolution ΔR

– Relies on bandwidth BW only

– Mm resolution: wideband (e.g. BW=100GHz, ΔR=1.5mm, )

300GHz Radar Imaging for Non-Destructive Detection of Material Defects


Integrated Radar Survey

• CMOS radar is desired

– Low cost

– Integration with analog and digital circuits

• Bandwidth of CMOS radars is limited

• Wideband FMCW radar issues– Performance fluctuation

– Chirp signal generation


Outline

• Introduction

• Comb Radar



• Conclusion


CH5

CH4

CH3

CH2

CH1t

f

Comb Radar Concept

• Divide a single wideband channel into N narrowband channels

• Make these N channels operate simultaneously

• Multi-tone operation looks like a comb

ΔT=Tm/N

N=5

ΔB=BW/N

TX

signal

Echo

t

f N=5

BW

t

f

ΔT

ΔBt

f

Tm

BW

TX signal

Echo

fCH1 CH5CH2 CH3 CH4


Comb Radar System Diagram

CH2TRX

÷2

CH1 TRX

÷2

IF1 IF2

10GHz

220~240GHz

55~60GHz

13.75~15GHz Multiplier(x4)

CH3TRX

÷2

IF3 CH4TRX

÷2

IF4TRX5

IF5

75~80GHz

300~320GHz

LO IQ (5GHz)SSB

Up-Mixer

Buffer

240~260GHz 260~280GHz 280~300GHz

Divider

External FMCW

Doubler1(x2)

Doubler2(x2)

SlotBalun

MatchingNetwork

SIFSquare-LawMixer

Amplifier

STX

SRXBPFLNA

Target

CH1TRX


Phase of IF Signals

• For Channel N, the TX signal is

𝑆𝑇𝑋 ,𝑁 𝑡 = cos 2𝜋𝑓𝑐,𝑁 +𝜋∆𝐵

𝛥𝑇𝑡 𝑡 +𝜑𝑁

𝑆𝑅𝑋,𝑁 𝑡 = cos 2𝜋𝑓𝑐,𝑁 +𝜋∆𝐵

𝛥𝑇 𝑡 −𝜏 (𝑡 −𝜏) +𝜑𝑁

𝑆𝐼𝐹,𝑁 𝑡 = cos(2𝜋∆𝐵

𝛥𝑇𝜏𝑡+2𝜋𝑓𝑐,𝑁𝜏)

• The echo signal (τ<<ΔT) is

• The band-pass-filtered IF signal is

• The phase of IF signal 𝜑𝐼𝐹,𝑁 has no initial RF phase 𝜑𝑁

= 𝜑𝐼𝐹,𝑁 𝑡

Initial RF phase

MN

SIF

STX

SRX

BPFLNA

Square-LawMixer

τ


Phase of IF Signals

• The phases of adjacent IF signals are continuous despite of their initial phases

CH N+1

TRX

CH N

TRX

IF N IF N+1

Target

τ

𝜑𝐼𝐹,𝑁+1 𝑡0 =2𝜋∆𝐵

𝛥𝑇𝜏𝑡0 + 2𝜋𝑓𝑐,𝑁+1𝜏

𝜑𝐼𝐹,𝑁 𝑡0 + ∆𝑇 =2𝜋∆𝐵

𝛥𝑇𝜏 𝑡0 + ∆𝑇 + 2𝜋𝑓𝑐,𝑁𝜏

𝜑𝐼𝐹,𝑁 𝑡0 + 𝛥𝑇 = 𝜑𝐼𝐹,𝑁+1 𝑡0

ΔB

ΔT

TX Echo

t

fRF

CH N

CH N+1

t

VIF

t

VIFCH N

CH N+1

fc,N

τ

t

Stitched IF

2ΔT


Stitching Process

• IF signals are directly stitched in time domain after calibrations

IF1Stitched IF

t

IF2

IF3

IF4

IF5

IF1 IF2 IF3 IF4 IF5De-Chirp

Tm

Calibration

ΔT=Tm/5

CH5

CH4

CH3

CH2

CH1t

RF

ΔT


Compared with Single Channel Radar

• More linear chirp signal

t

f

Tm=5ΔT

BW

ΔTt

f

5×

• SNR is improved

• Flatter frequency responses • Finer velocity resolution

∆𝑣 =λ

2𝑁𝑇𝑓𝑟𝑎𝑚𝑒

ferror

Chirp Signal

t

f


Outline

• Introduction

• Comb Radar



• Conclusion


Comb Radar System Diagram

• Total bandwidth:

5×20GHz=100GHz

• Scalable bandwidth

extension

• Single antenna

solution for each

transceiver: 5

antennas, coupling?

Doubler1(x2)

Doubler2(x2)

SlotBalun

MatchingNetwork

Square-LawMixer

Amplifier

BPFLNA

CH2TRX

÷2

CH1 TRX

÷2

IF1 IF2

10GHz

220~240GHz

55~60GHz

13.75~15GHz Multiplier(x4)

CH3TRX

÷2

IF3 CH4TRX

÷2

IF4TRX5

IF5

75~80GHz

300~320GHz

LO IQ (5GHz)SSB

Up-Mixer

Buffer

240~260GHz 260~280GHz 280~300GHz

Divider

External FMCW

CH1TRX


On-Chip Antenna Background

Slot Antenna Patch AntennaSubstrate Integrated

Waveguide (SIW)

Expensive Silicon Lens

Need No Need No Need

Bandwidth Wide Narrow Narrow

Inter-Antenna Coupling

Medium Large Small

Example

[R. Han, ISSCC 2012] [R. Han, JSSC 2013] [S. Hu, JSSC 2012]

Slot Antennas


SIW Cavity and Slot

• Eigenmode simulation


SIW Cavity with Orthogonal Slots

• Four modes


SIW Orthogonal Slot Antenna

• Multiple resonant modes due to orthogonal slots in SIW cavity

• Tune size parameters to arrange mode frequencies

220 240 260 280 300 320

-20

-15

-10

-5

0

Sim

ulat

ed S

11 w

ith M

N (

dB)

Frequency (GHz)

Lslot1

Lslot2

Feed

Wcav

Lcav

f

f

Size Tuning

Mode Frequencies


SIW Orthogonal Slot Antenna

• Wide bandwidth (~40GHz, 14.8%)

• 0dBi peak gain

• Linear polarization (axial ratio > 11.6dB)

250 260 270 280 29010

15

20

25

30

Pea

k G

ain

(dB

)

Axi

al R

atio

(dB

)

Effi

cien

cy (

%)

Frequency (GHz)

-20

-15

-10

-5

0

5

0

5

10

15

20

25

220 240 260 280 300-70

-60

-50

-40

-30

Sim

ulat

ed A

nten

na

(CH

2&C

H3)

Cou

plin

g (d

B)

Frequency (GHz)

• Low coupling (< -31dB)

• 20.5% efficiency


Input Multiplier, Buffer, and SSB Mixer

Buffer

Multiplier (X4)

Vb

OUT

LOI+ LOI- LOQ+ LOQ-I+

Q+

Q-

I-

To CH1 TRX

I+ Q+ Q-I-

SSB Up-Conversion Mixer

IF1

55~60GHz

13.75~15GHz IN

Multiplier(x4)

CH1 TRX

÷2

5GHz

10GHz

13.75~15GHz

IN

55~60GHz 60~65GHz

Multiplier (x4)

Buffer SSB Mixer

To CH1 TRX

OUT

OUT

IN


Doubler1 and Folded Slot Balun

Doubler1(x2)

Doubler2(x2)

SlotBalun

MatchingNetwork

Square-LawMixer

Doubler1Vb

IN

BPFLNA

Doubler1

Balun

ININT

INT OUTIN

INT

OUT


Folded Slot Balun

• Nearly perfect differential output

– 50GHz (45%) bandwidth

– 1.3dB insertion loss

– 0.05dB/0.5° amplitude/phase errors

λ/4 Resonator

IN

OUT

-3dB

IN

OUT


Cascaded Neutralized Amplifier

Doubler1(x2)

Doubler2(x2)

SlotBalun

MatchingNetwork

Cascaded Neutralized Amplifier

IN OUT

OUTIN


Doubler2

Doubler1(x2)

Doubler2(x2)

SlotBalun

MatchingNetwork

Doubler2

To RXTo MN

IN+ IN-

Output Frequency (GHz)200 210 220 230 240 250 260

Outp

ut P

ow

er

(dB

m)

2

0

-2

-4

-6

-8

Output Frequency (GHz)200 210 220 230 240 250 260

10

Conve

rsio

n L

oss

(dB

)9

8

7

6

5

4

IN

OUT

OUT


Multi-Stub Matching Network

Doubler1(x2)

Doubler2(x2)

SlotBalun

MatchingNetwork

Square-LawMixerL1

L1

L2

L2

L3

L3

L4

L4

L5

L5

L6

L6

L7

L7

IN OUT

Layout

Frequency (GHz)220 230 240 250 260 270210200190S

-Para

mete

rs (

dB

)

S21

S11

S22

0

-10

-5

-15

-20

BPFLNA


Receiver

• Square-law mixer for

single antenna solution,

passive circuit for

smaller flicker noise

• Self-biased LNA with

high-pass input to

suppress unwanted low

frequency components

Doubler1(x2)

Doubler2(x2)

SlotBalun

MatchingNetwork

IFSquare-LawMixer

IF

VDD

From TX & Antenna

Square-Law Mixer

Vb

BPFLNA

To External BPF, VGA, and ADC

Receiver BPFLNA

Cb


Outline

• Introduction

• Comb Radar



• Conclusion


Chip and PCB Photograph

• TSMC 65nm bulk CMOS

technology

• Area: 2.5mm by 2.0mm

• Total power consumption:

840mW

SIW Antenna

2.0

mm

2.5 mm

BufferSSB

Mixer

Divider

Doubler1Balun

Amplifier

Multiplier(X4)

RXDoubler2

Matching

Network

TPX Plastic Focus Lens


Transmitter Mode Measurement

• Total EIRP without lens: 0.6dBm

• Total EIRP with lens: 20dBm

• Fluctuations: within 8.8dB

200 220 240 260 280 300 320 340

-60

-40

-20

0

20

w/ lens

w/o lens

EIR

P(d

Bm

)

Frequency (GHz)

Fluctuations

VDI

Extender

(Receiver)

Signal

Generator

(E8257D)

Signal

Generator

(N5173B)

Horn

Antenna

LO

10GHz

13.75~15GHz

RF

PCB

Spectrum

Analyzer

(N9020A)

Signal

Generator

(83732B)

LO

IF

Lens

(w/, w/o)Setup is calibrated by PM5


Transmitter Mode Measurement

0.1 1 10 100 1000-120

-100

-80

-60

-40

-20

Mea

sure

d T

X P

hase

Noi

se (

dBc/

Hz)

Frequency Offset (kHz)

-90

-60

-300

30

60

90

E Plane

H Plane

Radiation Pattern (CH3, w/o Lens)

0dB-10dB

• Friis equation is met at far-field

• Antenna radiation pattern 3dB beamwidth: 90°

• Phase noise: better than -100dBc/Hz @1MHz

∝1/Distance2

Distance in log scale (cm)

Mea

sure

d P

ower

Pm

eas

(dB

m)

Calculated E

IRP

(dBm

)

0.5 1 2 4 8 16 32

-50

-40

-30

-20

-15

-10

-5

w/o lens


Receiver Mode Measurement

• Minimum SSB NF including antenna loss: 22.8dB

• Fluctuation of NF: 14.6dB

• Receiver gain: 22.2dB

200 220 240 260 280 300 320 340-50

-40

-30

-20

-10

0

10

20

30

Frequency (GHz)

Gai

n (d

B)

20

30

40

50

60

70

80

90

100

Noi

se F

igur

e (d

B)RX

Gai

n (d

B)

RX

Noise F

igure (dB)

w/o lens

VDI

Extender

(Transmitter)

Signal

Generator

(E8257D)

Signal

Generator

(N5173B)

Horn

Antenna

LO

10GHz

13.75~15GHz

RF

PCB

Signal

Generator

(83732B)

Spectrum

Analyzer

(N9020A)

IFRF

Setup is calibrated by PM5


FMCW Radar Measurement Setup

DDSAD9164

Multipliers(x4)

CombRadarChip

13.75~15GHz

NI PXI-5105

Digitizer

5 IFsSignal Generator

10GHz BPFsVGAs

FMCW

LO To PC

ΔB

ΔT

Useful signals

Over-chirping


Radar Signal Calibration

• Amplitude mismatch

– Gain mismatch among channels

• Phase mismatch

– Matching network delay mismatch: fixed

– Antenna off-axis: range should be large (>20cm)

• Calibration method [J. Grajal, TMTT 2015]

– Reference: one single-point like target

– One-time calibration

Amplitude/Phase

Calibration

Raw Data

Reference Target

Calibration Data

IF Stitching


Range Accuracy Measurement

• Measured distance matches real distance


Range Resolution Measurement

2.5mm

• Two targets with

2.5mm distance

• Hamming window

• One channel

• 20GHz



2.5mm

• Three channels

• 60GHz



2.5mm

• Five channels

• 100GHz


Comparison Table


Outline

• Introduction

• Comb Radar



• Conclusion


Conclusion

• Comb radar for wideband THz applications

– Flatter frequency responses

– More linear chirp signal

– Finer velocity resolution

– Improved SNR

– Scalable bandwidth extension

• A five channel comb radar with 100GHz bandwidth was

demonstrated in 65nm bulk CMOS technology


Acknowledgements

• Chip fabrication: TSMC University Shuttle Program

• Measurements: Prof. Charlie Sodini, Prof. Tomás Palacios,

Qingyu Yang, Mohamed I. Ibrahim, and Nathan Monroe (MIT);

Pu Wang, and Rui Ma (Mitsubishi Electric Research Labs)

• Funding: NSF CAREER award (ECCS-1653100), MIT Center of

Integrated Circuits and Systems (CICS), and a gift fund from

TSMC


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A Terahertz FMCW Comb Radar in 65nm CMOS with 100GHz … · © 2020 IEEE 4.8: A Terahertz FMCW Comb Radar in 65nm CMOS with 100GHz Bandwidth International Solid-State Circuits Conference