heterodyne sensing cmos array with high density …...rtu1b-4 2018 ieee mtt-s radio frequency...

RTu1B-4

2018 IEEE MTT-S Radio Frequency Integrated Circuits Symposium

10-12 June 2018, Philadelphia, PA

RTu1B-4

Heterodyne Sensing CMOS Array with High

Density and Large Scale: A 240-GHz, 32-Unit

Receiver Using a De-Centralized Architecture

Zhi Hu, Cheng Wang, and Ruonan Han

Massachusetts Institute of Technology

Cambridge, MA, USA

1

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• Introduction

• Array Architecture

• Multi-functional Heterodyne Pixels

• Phase Locking Circuitry

• Measurement Results

• Conclusion

2

Outline

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3

Terahertz Radar as an Important Sensing Mode

• Multiple sensing modes are needed in navigation applications

where safety is a priority

– Examples: self-driving cars, unmanned aerial vehicles, etc.

[Source: roboticsandautomationnews.com]

[Source: Getty Images]

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4

Terahertz Radar as an Important Sensing Mode

• Multiple sensing modes are needed in navigation applications

where safety is a priority

– Examples: self-driving cars, unmanned aerial vehicles, etc.

[Source: roboticsandautomationnews.com]

[Source: Getty Images]

[National Research Council, Assessment of Millimeter-Wave and Terahertz Technology

for Detection and Identification of Concealed Explosives and Weapons, 2007]

~0.01 dB/m @ 240 GHz

• Terahertz sensing is an important complement to light-based

sensing (e.g. LiDAR)

– Sub-THz waves have much lower propagation loss than light

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5

Possible Path Towards Sharp THz Beam

• If we use a single heterodyne receiver array,

– to obtain 1° beam width, an area of 6cm x 6cm (~ 10,000 units) is needed at 240 GHz

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6

Possible Path Towards Sharp THz Beam

10×10 Sparse

TX Array

10×10 Dense

RX Array

• One possible solution is based on the two-way array pattern

– On-board sparse TX array generates sharp beams

– On-chip dense RX array synthesizes single beam to filter out TX sidelobes -- with relaxed, but still high, scale requirement

-30 -15 0 15 30-30

-20

-10

0

RX Pattern

TX Pattern

Convoluted Pattern

Po

wer

Resp

on

se (

dB

)

Angle (Degree)

• If we use a single heterodyne receiver array,

– to obtain 1° beam width, an area of 6cm x 6cm (~ 10,000 units) is needed at 240 GHz

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7

Review of Previous On-Chip THz Sensing Arrays

[E. Öjefors, et al., JSSC, 2009] [R. Al Hadi et al., JSSC, 2012] [R. Han et al., JSSC, 2013]

• Direct (Square-Law) Detector Arrays (large scale)

• Techniques of building large-scale direct detector arrays have become mature

• Limitations of direct detection

Low responsivity and low SNR, due to limited received RF power (PIF ∝ PRF2)

Coherence of RF signals is lost, thus unable to perform beam-forming (electrical scanning)

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8

Review of Previous On-Chip THz Sensing Arrays

2 x 2 array [K. Statnikov, et al., TMTT, 2015] 8-unit array [C. Jiang, et al., JSSC, 2016]

• Heterodyne Detector Arrays (small scale)

• Strengths of heterodyne detection

High responsivity and high SNR, by leveraging high LO power (PIF ∝ PLO ∙ PRF)

Coherence of RF signals is preserved, thus inherently capable of beam-forming

• There are still challenges of designing large-scale heterodyne detector arrays to form sharp beam

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• Introduction





• Conclusion

9

Outline

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10

RX Chip: Centralized vs. De-Centralized Arrays

On-Chip

Antennas

Sub-THz

Mixers

On-Chip

Sub-THz PLL

Sensing

Pixel

Sub-THz LO

Signal, fLO

fIF

÷N

PFDLPF

Reference

Clock, fref

• Centralized array relies on a single LO source, however,

LO power of each unit scales down as array scales up

Long LO feed lines are lossy and hard to route 8-unit array [C. Jiang, et al., JSSC, 2016]

• Example

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11

RX Chip: Centralized vs. De-Centralized Arrays

1 2 4 8 16 32-115

-110

-105

-100

-95

Ph

ase

No

ise

(dB

c/H

z,

f

=1

MH

z)

Number of Coupled Units

On-Chip

Antennas

Sub-THz

Mixers

On-Chip

Sub-THz PLL

Sensing

Pixel

Sub-THz LO

Signal, fLO

fIF

÷N

PFDLPF

Reference

Clock, fref

Coupled

Local

Oscillators

Phase/Frequency Control, vctrl

Sensing

Pixel

Sub-THz LO

Signal, fLO

On-Chip Phase-

Locked Loop

fIF

On-Chip

Sub-THz PLL

÷N PFD

LPF

Reference

Clock, fref

On-Chip

Antennas

Sub-THz

Mixers

• De-Centralized array ensures every unit having an LO source

LO sources are coherently coupled; corporate feed is thus eliminated

Oscillator power requirement is relaxed

Bonus: LO phase noise improves as more units are coupled

• Centralized array relies on a single LO source, however,

LO power of each unit scales down as array scales up

Long LO feed lines are lossy and hard to route

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12

Challenges of Scaling and Our Solutions

Coupled

Local

Oscillators


Sensing

Pixel

Sub-THz LO

Signal, fLO

On-Chip Phase-

Locked Loop

fIF

On-Chip

Sub-THz PLL

÷N PFD

LPF

Reference

Clock, fref

On-Chip

Antennas

Sub-THz

Mixers

• Density challenge:

– Within λ/2 ∙ λ/2 area, antenna,

oscillator, mixer, coupler etc.

needs to be incorporated

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13

Vctrl

32 IF

Signals

Data

Processing

RF Receiving

from Pattern 1

75-MHz Reference

λRF / 2

ILFD (÷)Divider ChainPFDCharge PumpLPF

LO Signal

RF Receiving

from Pattern 2

Data

Processing

λR

F / 2

Slot

Antenna

Self-Oscillating

Harmonic Mixer

(SOHM)

Slotline w/

LO signalLO Coupling

MUX(off-chip)

λR

F / 4






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14

• Self-Oscillating harmonic mixer

(SOHM) employed

– Oscillator and mixer condensed

into one component

• Slotline-resonator-based

oscillator coupling employed

• Two interleaved 4x4 array

integrated (Aunit = λ/2 ∙ λ/2)

Vctrl

32 IF

Signals

Data

Processing

RF Receiving

from Pattern 1

75-MHz Reference

λRF / 2

ILFD (÷)Divider ChainPFDCharge PumpLPF

LO Signal

RF Receiving

from Pattern 2

Data

Processing

λR

F / 2

Slot

Antenna

Self-Oscillating

Harmonic Mixer

(SOHM)

Slotline w/

LO signalLO Coupling

MUX(off-chip)

λR

F / 4






RTu1B-4



• Introduction





• Conclusion

15

Outline

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16

EM Structure of a Single Cell

• The array consists of 16 cells,

each cell contains 2 units

• The boundaries of each unit is well-defined, as

a result of LO coupler design

• The unit is structurally and electrically symmetric; a PEC

boundary (AB) can be drawn in the middle at f0

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17

Highlight I: Multifunctional Structures

Vctrl

45

°@f 0

45°@f0

VDD

TL3

TL1

TL2

TL4

VIF

TL5

TL4'

TL1'

60°@f0 C3

C2 C1

TL3'

C4

90°@2f0

EM structure as reference

• TL4 and TL4’ are slot antennas

• TL3 and TL3’ are resonator and coupler

of oscillators

• TL1, TL1’, TL2, and TL5 are integral

components of oscillators

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18


TL3

TL1

TL2

TL4

TL5

Virtu

al G

rou

nd

C2

C1

C3

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19


TL3

TL1

TL2

TL4

TL5

Virtu

al G

rou

nd

C2

C1

C3

TL3

TL1

TL4

C1M1

Self-Feeding Oscillator

Enhance

instability

Antenna

(Resonator II)

Coupler

(Resonator I)

[Han et al., JSSC, 2013]

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20


TL3

TL1

TL2

TL4

TL5

Virtu

al G

rou

nd

C2

C1

C3

TL3

TL1

TL4

C1M1


Enhance

instability

Antenna

(Resonator II)

Coupler

(Resonator I)


V2f0Vf,RF

Vf,IFShort @ f0

TL1

TL3

from

oscillator

from

antenna

+

Oscillates

Down-converts

Receives

RTu1B-4



21


TL3

TL1

TL2

TL4

TL5

Virtu

al G

rou

nd

C2

C1

C3

• Self-oscillating harmonic mixer (SOHM) can be regarded as an oscillator that

– Oscillates at f0 = 120 GHz and simultaneously generates LO signal fLO = 2f0 = 240 GHz

– Receives RF power from resonator (TL4, Resonator II)

– Down-converts RF to IF, i.e. fIF = fRF – 2f0 (using the non-linearity of the transistor)

• Oscillator is optimized to the optimal phase condition by choosing proper ZTL1 and φTL1

TL3

TL1

TL4

C1M1


Enhance

instability

Antenna

(Resonator II)

Coupler

(Resonator I)


V2f0Vf,RF

Vf,IFShort @ f0

TL1

TL3

from

oscillator

from

antenna

+

Oscillates

Down-converts

Receives

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22

Highlight II: Near-field Interference

TL3

TL1

TL4

C1M1

Antenna

(Resonator II)

Coupler

(Resonator I)

• Resonator I and II are for coupling and radiation cancelling

• For explanation, E-field distributions are needed

RTu1B-4



23

E- Field

Power Flow TL2

TL5

dc

b a

Highlight II: Near-field Interference at f0

• At f0 = fLO/2, waves in TL3 induce coupling between

oscillators

• E-Field polarizations in TL3 and TL4 of adjacent units

ensure radiation cancellation at f0

TL3

TL1

TL4

C1M1

Antenna

(Resonator II)

Coupler

(Resonator I)



TL1'

TL4 TL4'

TL1

TL3'TL3

C4Dummy

C3

Current

Source

TL2

TL5

• Full-wave Simulation (ports at drains are driven)

• Theoretical prediction

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24

E- Field

Weak Power

LeakageTL2

TL5Cgd

LO Power

Confinement

Highlight II: Near-field Interference at 2f0

• At 2f0 = fLO, waves are largely confined within the transistor

• Potential radiation is cancelled due to polarizations

TL3

TL1

TL4

C1M1

Antenna

(Resonator II)

Coupler

(Resonator I)



• Full-wave simulation (ports at drains are driven)


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25

E- Field

Power

InjectionTL2

TL5

Highlight II: Near-field Interference at fRF

TL3

TL1

TL4

C1M1

Antenna

(Resonator II)

Coupler

(Resonator I)



• At fRF, waves are received by antennas since they are from

a far-field source with the same polarization

• Down-converted IF signals are thus out-of-phase

• Full-wave simulation (ports at antennas are driven)


RTu1B-4



26

E- Field

Power

InjectionTL2

TL5

E- Field

Weak Power

LeakageTL2

TL5Cgd

LO Power

Confinement

E- Field

Power Flow TL2

TL5

dc

b a

Recap: Multi-functionality + Near-field Interference

TL3

TL1

TL4

C1M1

Antenna

(Resonator II)

Coupler

(Resonator I)



• At 2f0, waves are largely confined within the transistor

• Potential radiation is cancelled due to polarizations

• At f0, waves in TL3 induce coupling between oscillators

• E-Field polarizations in TL3 and TL4 of adjacent units ensure

radiation cancellation at f0• At fRF, waves are received by antennas since they are

from a far-field source with the same polarization

RTu1B-4



27

Simulation Results of SOHM Performance

• DC Power per unit: 43.2 mW

• Conversion loss (CL): 16 dB (with 50-Ω output load)

• Noise figure (NF): 46.5dB at fIF =5 MHz; 19.3 dB at fIF =100 MHz

1k 10k 100k 1M 10M-120

-100

-80

-60

-40

-20

0

Ph

ase N

ois

e o

f f 0

(d

Bc/H

z)

Frequency Offset (Hz)

10k 100k 1M 10M 100M 1G

-170

-160

-150

-140

-130

IF N

ois

e P

SD

(d

Bm

/Hz)

Frequency (Hz)

90 135 180 225 270-10

0

10

20

Dir

ec

tiv

ity

in

H-P

lan

e (

dB

i)

Phi (degree)

-20

-10

0

10

20

90 135 180 225 270-10

0

10

20

Dir

ec

tiv

ity

in

E-P

lan

e (

dB

i)

Theta (degree)

-20

-10

0

10

20

• Antenna peak directivity: 4.8 dB; antenna efficiency: 40 %

Simulated beam-steering results

Simulated IF noise floor

Simulated f0 phase noise

RTu1B-4



• Introduction





• Conclusion

28

Outline

RTu1B-4



29

Overview of the Phase Locking Circuitry


Sub-THz LO

Signal, fLO

On-Chip Phase-

Locked Loop

÷N PFD

LPF

Reference

Clock, fref

RTu1B-4



30

Overview of the Phase Locking Circuitry

• Bottom two pixel units inject a small amount of waves at f0 = 120 GHz into the divider

• PLL components generate the VCO control voltage for the entire array

• Due to array-wide coupling, all units are locked


On-Chip Phase-

Locked Loop

÷N PFD

LPF

Reference

Clock, fref

Pixel at

Row 8, Col 2

Pixel at

Row 8, Col 3

Vf0, DC

LO Power to ILFD

Array

Boundary

ILFD Switch

45°@f045°@f0

To Oscillators

54°@f022°@f0

22°@f0

ILFD

Equivalent Circuit

ILFD

≈ Open

AC Cap AC Cap

AC CapSub-THz LO

Signal, fLO

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31

Design of the 120-GHz Divide-by-16 Divider

• 1st stage: div-by-4 ILFD, based on finj = 4fosc mixing with 3fosc

• 2nd stage: div-by-4 ILFD, based on injected signals modulating the current sources of the ring oscillator

• Total DC power consumption: 10.5 mW

VT

VT

VT

VDD

Vf0/16

Vf0

VP

VDD,osc

Vtune VDD, buf

VB

Vf0/4, p

VDD, buf

VB

Vf0/4, n

0.54nH

0.29nH0.29nH

0.54nH

10kΩ

10kΩ

2pF2pF

VTVT

4 μm 4 μm

10 μm

6 μm

3 μm

10kΩ

20 μm

6 μm

6 μm

6 μm 6 μm

6 μm 6 μm

6 μm

6 μm 6 μm

6 μm 6 μm

6 μm

6 μm 6 μm

6 μm 6 μm

6 μm

6 μm 6 μm

6 μm

1 μm

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• Introduction





• Conclusion

32

Outline

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33

Vctrl Output Reference

InputDivider

Output

PLL DC

Biases

Arra

y D

C B

ias

es

MUX DC Biases

MUX Output 1

Chip

MUXADG726

High-Res

Silicon Wafer

Drilled

PCB

MUX Output 2

CMOS Chip

Hemispheric,

High-Res

Silicon Lens

Die Photo and Chip Packaging Details

Array

Boundary

Terminations

ILFD &

Buffers Dividers, PFD,

Charge Pump

IF Outputs

Boundary

Terminations

1.4 mm

2.0

mm

1.1 mm

1.1

mm

Interface

• Silicon lens is attached to the backside of the chip (backside radiation)

• Off-Chip multiplexer is used to select the desired IF signal from 32 outputs

• Technology: 65nm CMOS; chip area 2.8 mm2 (1.21 mm2 for the array)

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34

Power Supply Agilent N9020A MXA

Spectrum Analyzer

WR-3.4 Antenna

VDI WR-3.4Frequency Extender

(TX Mode)

ZFL-500LN Amplifiers

HP 83732BSignal Generator

fRF / 18

fIF

fLO / 3200

10 MHz Sync

...

LDO Board (ADP7157)

Keysight E-8257DSignal Generator

DC

Biases

fRF

Silicon Lens

Silicon Wafer

Chip

10cm

-20 dBm

-120 dBm

Center: 73.2 MHz

Span: 200 kHz

RBW: 10 Hz

Overview of the Chip Measurement

VDI 220-to-320GHz

Frequency Extender

Chip and PCB Spectrum

Analyzer

Signal

Generator

• VDI WR-3.4 extender is used as the RF source

• Frequency reference of the chip and the VDI

source are synchronized

• Locking range of the array (obtained from

divider output): 232.96 GHz – 234.88 GHz

Spectrum of the divider output

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35

Measured IF Spectra at Low/High Frequencies

• Flicker noise dominates until ~ 450

MHz (IF amp BW = 500 MHz)

IF noise spectrum (from spectrum analyzer)

White Noise Floor

0 dBm Start: 1.0 MHz

Stop: 500.0 MHz

RBW: 100 kHz

-100 dBm

4.6 MHz

475 MHz

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36

Noise Floor when

RF Signal is Absent

4.6-MHz

IF Signal63 dB SNR(normalized to

1-Hz RBW)

0 dBm

-100 dBm

Center: 4.60 MHz

Span: 2.00 MHz

RBW: 100 Hz

Noise Floor when

RF Signal is Absent

475-MHz

IF Signal87 dB SNR(normalized to

1-Hz RBW)

0 dBm

-100 dBm

Center: 475 MHz

Span: 50.0 MHz

RBW: 100 kHz

Measured IF Spectra at Low/High Frequencies

• Flicker noise dominates until ~ 450

MHz (IF amp BW = 500 MHz)

• At 4.6 MHz (below corner frequency),

SNR = 63 dB (RBW = 1Hz)

• At 475 MHz (beyond corner frequency),

SNR = 87 dB (RBW = 1Hz)

• Other pixels are also locked; they have

similar responses, and their fIF all shifts

simultaneously as fref shifts

IF noise spectrum (from spectrum analyzer)

IF spectrum (fIF = 4.6 MHz)

IF spectrum (fIF = 475 MHz)

White Noise Floor

0 dBm Start: 1.0 MHz

Stop: 500.0 MHz

RBW: 100 kHz

-100 dBm

4.6 MHz

475 MHz

RTu1B-4


10-12 June 2018, Philadelphia, PA37

Measured 4.6-MHz IF of Some Other Units

Row 3, Col 4Row 2, Col 2Row 1, Col 3

Row 7, Col 2 Row 8, Col 2Row 6, Col 3

RTu1B-4



38

90 120 150 180 210 240 270-25

-20

-15

-10

-5

0

5

10

Measured Pattern

Simulated Pattern

Theta (Degree)E-P

lan

e A

nte

nn

a D

ire

cti

vit

y (

dB

i)

90 120 150 180 210 240 270-25

-20

-15

-10

-5

0

5

10

Measured Pattern

Simulated Pattern

Phi (Degree)H-P

lan

e A

nte

nn

a D

ire

cti

vit

y (

dB

i)

Antenna Pattern and Performance Evaluation

• Conversion gain (dB)

CG = PIF – PRF , where

PIF = PIF, analyzer – Gamp, and

PRF = PRF, TX + DTX + GRX – 20log10(λ/(4πd))

• Noise figure (dB)

NF = Pnoise – (-174 dBm) – CG, where

Pnoise = 10log10(10(Pnoise, analyzer – Gamp)/10 – 10-17.4)

(considering NFamp = 3dB)

• Here, we have Gamp = 49 dB, PRF,TX = -7.1 dBm, DTX = 24 dBi,

DRX = 6.0 dB, ηRX = 40 % (simulated), λ = 1.28 mm, d = 0.1 m

• For fIF = 475 MHz (beyond corner frequency), CG = -42.4 dB,

NF = 44.2 dB

Measured and simulated antenna patterns (E-Plane)

Measured and simulated antenna patterns (H-Plane)

Define Sensitivity = NEP ∙ √1000Hz = -174 dBm + NF + 30dB;

for fIF = 475 MHz, Sensitivity = 0.105 pW

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39

Measured Phase Noise of the LO Signal

Down-converted 2f0

-10 dBm

-110 dBm

Center: 240 MHz

Span: 2.00 MHz

RBW: 20 Hz -84 dBc/Hz @ 1-MHz Offset

-40 dBc/Hz @ 1-kHz Offset

0 dBc/Hz

-100 dBc/Hz

Power Supply Agilent N9020A MXASpectrum Analyzer

WR-3.4 Antenna

HP 83732BSignal Generator

2f0 - Δf

Δf fLO / 3200

10 MHz Sync

...

LDO Board (ADP7157)

Keysight E-8257DSignal Generator

DC

Biases

2f0

VDI WR-3.4Frequency Extender

(RX Mode)Near Field

ZFL-500LN Amplifiers

• VDI extender is placed very close to the chip to capture the

leaked near-field radiation at 2f0

• Measured 2f0 phase noise at 1 MHz offset is -84 dBc/Hz

Spectrum of the leaked 2f0 signal Measured phase noise of the 2f0 signal

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40

Performance Comparison

References This Work [5] [1] [2] [3]

Detection Method Heterodyne Detection Square-Law (Direct) Detection

Array Size 4x8 8 4x4

Array Scalability Yes No Yes Yes Yes

RF Frequency (GHz) 240 320 280 320 280

Sensitivity (pW) 0.105 † 71.4 917 1080 250

DC Power (mW) 980 117 6 38 180

Chip Area (mm2) 2.80 3.06 5.76 6.76 6.25

Technology 65nm CMOS 130nm SiGe 130nm CMOS 180nm SiGe 130nm SiGe

Notes:† Calculated based on PIF and Pnoise at fIF = 475 MHz

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41

Performance Comparison

References This Work [5] [1] [2] [3]

Detection Method Heterodyne Detection Square-Law (Direct) Detection

Array Size 4x8 8 4x4

Array Scalability Yes No Yes Yes Yes

RF Frequency (GHz) 240 320 280 320 280

Sensitivity (pW) 0.105 † 71.4 917 1080 250

DC Power (mW) 980 117 6 38 180

Chip Area (mm2) 2.80 3.06 5.76 6.76 6.25

Technology 65nm CMOS 130nm SiGe 130nm CMOS 180nm SiGe 130nm SiGe

Notes:† Calculated based on PIF and Pnoise at fIF = 475 MHz

RTu1B-4



• Introduction





• Conclusion

42

Outline

RTu1B-4



• For the first time, heterodyne receiver array has achieved large scale and

high density that are comparable to those of square-law detector arrays

• Our array improves the sensitivity by ∼ 680x compared with the 8-unit

heterodyne receiver array, and by ∼2400x compared with the best square-

law detector arrays

• Scalability and sensitivity improvements make sub-THz array technology a

more promising candidate for the implementation of high-resolution beam-

forming imagers in the future

43

Conclusion

RTu1B-4



• The authors would like to thank

–Guo Zhang, Jack Holloway and Dr. Xiang Yi at MIT for technical

discussions

–Dr. Andrew Westwood and Kathleen Howard at Keysight Inc. for their

support to the experimental instruments

• This work was supported by

– The National Science Foundation CAREER Award (ECCS-1653100)

– Taiwan Semiconductor Manufacturing Company (TSMC)

– The Singapore-MIT Research Alliance

44

Acknowledgement

RTu1B-4



RTu1B-4

Heterodyne Sensing CMOS Array with High

Density and Large Scale: A 240-GHz, 32-Unit

Receiver Using a De-Centralized Architecture

Zhi Hu, Cheng Wang, and Ruonan Han

Massachusetts Institute of Technology

Cambridge, MA, USA

45

heterodyne sensing cmos array with high density …...rtu1b-4 2018 ieee mtt-s radio frequency...

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