May 9, 20161

A mm-Wave Low-Power Transceiver with up to 80 Gbit/s for an Integrated Wireless interconnect in Bulk CMOS

Prof. Emanuel Cohen

Technion

May 9, 20162

• Introduction to Interconnect

• Electrical Interconnect Solutions

• Wireless interconnect - Transceiver Implementation and Testing

• Summary and Conclusions

Agenda

May 9, 20163

Interconnect bottleneck -Introduction

May 9, 20164

Interconnect Gap

• Big Data Era: Increasing gap between I/O bandwidth requirements and limited I/O pin numbers for Chip-to-Chip communications

I/O bandwidth: 2X /2years

•I/O Pins: slowly increase

Need increasing growth of bandwidth

density and power efficiency

D. Huang, IEEE HSD Workshop 2011, Santa Fe

May 9, 20165

Interconnect options and target– Wireline big and heavy connectors through backplane

– Optical – high power and bulky integration, high accuracy connectors required.

– Wireless solution (near/far field) or mmW waveguides.

Servers interconnect >1m Chips interconnect – mm/cm range

May 9, 20166

Interconnect metrics

May 9, 20167

Chips interconnect 3D

• TeraByte/s Data-bandwidth TSV and Interposer Design for 3D-IC

May 9, 20168

Chips interconnect 2.5DMCM Packages

• 2.5D integration is a means to connect multiple die in a low-cost package

– Increase yield, lower manufacturing costs

• Efficient solution requires high-bandwidth, low-power SerDes

May 9, 20169

Electrical Interconnect Solutions

May 9, 201610

State of the art BB systems

• Move to PAM4 for doubling the bit rate – increase RX complexity

Takayasu Norimatsu, “A 25-Gb/s Multi-standard Serial

Link Transceiver for 50-dB Loss Copper Cable in 28-

nm CMOS” – ISSCC 2016

May 9, 201611

Advantages of Passband communication

• Channel BW is limited mainly by link impairments that create an SNR floor - to overcome it we need to invest in corrections (equalization) that increase power and complexity

• Dividing the spectrum into sub-band with limited BW allow us to create simple systems per channel.

• Passband signals can carry x2 information for same SNR and BB BW

Related advantages:• High freq passband decrease the antenna size for wireless system• High freq passband enable waveguide mode with low IL for high

distances

May 9, 201612

FDMA advantageExamples :

Sai-Wang Tam, “A Simultaneous Tri-band On-Chip RF-

Interconnect for Future Network-on-Chip” – VLSI 2009

Anat Rubin, “Dual Band 18.5Gbps Transmitter at60GHz and 80GHz in 65nm CMOS “ – EuMA 2013

May 9, 201613

Waveguide links

• Low loss at high frequency • Supports large distance (minimize ISI - with controlled dispersion)

Air-Filled Substrate Integrated Waveguide

Ha Il Song, “Plastic straw: future of high-speed

Signaling” - nature 2015

May 9, 201614

Increase capacity with freq @ modes

• Pitch becomes small at very high frequencies only

Nemat Dolatsha, “Analysis and Design of Multi-mode Dielectric Waveguide Interconnect with Planar Excitation”- PIERS 2013

May 9, 201615

Wireless interconnect -Example

May 9, 201616

–Evaluate Wireless Interconnect as complementary solution or potential replacement for today’s copper-based high-speed links

–Evaluate low power broadband (100-140 GHz) transceiver circuits in 28 nm bulk CMOS technology

–Combine RF CMOS with high gain on-package integrated antennas for short range high datarate wireless interconnects

–Introduce preliminary lab measurements confirming that wireless interconnects is a viable solution for future products

Objective

May 9, 201617

• Removes traditional transition losses and enables flexible architectures• Potential applications in servers, microservers and other devices

Benefits of Wireless interconnect

- Board, package and socket losses- Socket scalability with high IO count

- No socket or package transitions- Flexible interconnect point to multipoint

Die

Package

Board

Socket

May 9, 20161818

• Silicon: Design for wideband and low power

• Package: broadband/high efficiency antennas, low loss materials

• Testing: Modulate and demodulate wideband signals – equalization and channel learning

Wireless Interconnect Goals and Challenges

Targeted Specs (This work)

Transmission range 5 cm

Datarate per channel QPSK: 40 Gbps16 QAM: 80 Gbps

Efficiency < 4 pJ/bit (160mW @ 40Gb/s)

Technology 28 nm

Frequency (Bandwidth) 120 GHz (40 GHz)

May 9, 201619

Transceiver Architecture and Power Targets

RX

TX

Synt + LOD

• Requires external W- or V-band for LO and up to Ku-band for baseband signals Focus on bandwidth and power reduction techniques

• DC power consumption: 240 mW

• Direct conversion architecture

Amp/mutiplier

90d

PA

RFIC

LNA

PA

Antenna Package

DC connection

LO TX

90d

90d

Amp/mutiplier

Amp/mutiplier

Board

May 9, 201620

• Capacitive neutralization improves stability and gain at mm-wave frequencies

• Low-k transformers trade gain for matching bandwidth

High Frequency wide band Focus

Capacitive neutralization and low-k matching

Vi+ Vi-

Vo+Vo-

May 9, 201621

• Presents a virtual ground to odd harmonics.

• Combines even harmonic currents

• 18% efficiency at 4 dBm

Output100-140GHz

Input50-70GHz

Vb

C_Bal= 28fF C_Short=60fF

1.1V

C_Out=49fF

Dc Coupling=400fF

19um (0.5umx9.5x2)

X2 Frequency Multiplier – Push-Push Topology

100 110 120 130 140-12

-10

-8

-6

-4

-2

0

2

4

Frequency (GHz)

Pout

(dB

m),

Convers

ion G

ain

(dB

)

measured Pout

measured CG

Simulated Pout

Simulated CG

CG

PoutId+ Id-

Id

1.1V

Input50-70 GHz

Output100-140GHz

May 9, 201622

Passive Quadrature Generator

0

180

90

270

Load tune

Cg Cg

Cm Cm

L

L

Cg Cg

In

0 0.2 0.4 0.6 0.8 1 1.2-20

-10

0

10

20

30

Complex load tuning voltage (V)

I/Q

ph

ase

im

ba

lan

ce

(D

eg

.)

105 GHz

109 GHz

111 GHz

112 GHz

115 GHz

118 GHz

120 GHz

•Includes Phase Mismatch Tuning Capability

May 9, 201623

RX chain - LNA

• 4 stages CS CC

• Draws 18 mA from a 1.0 V supply.

•

•

690μm

370μm

240μm

510μm

May 9, 201624

• Downconversion mixer is passive• Baseband supply: 33 mW from a 1.5 V supply

Down Conversion Mixer and Baseband Topology

1300Ω 500Ω

16μm

14.4μm

25.6μm

14.4μm

24μm 24μm

11.8μm 11.8μm

12μm

12μm

12μm

12μm

LO-

LO+

LO+

Baseband amplifierMixer

BB output

From LNA

May 9, 201625

Receiver Performance – Die Level Test

95 105 115 125 13520

25

30

35

40

RF frequency (GHz)

Co

nve

rsio

n g

ain

(d

B)

Measured

Simulated

95 105 115 125 1358

9

10

11

12

RF frequency (GHz)

No

ise

fig

ure

(d

B)

Measured

Simulated

LOLNA

Baseband

Mixers

May 9, 201626

Thank You

RFp RFn

LOp

BB1p

BB1n

LOn

M1

7um

M2

7um

M5

11um

M6

11um

BB2p

BB2n

M3

14um

M4

14um

M7

11um

M8

11um

LOp

Vdd

TX chain

• Support 16-QAM modulation

• Gilbert cell RF DAC-Mixer

• Cross inverter connection for improved differential signals

May 9, 201627

• Measured Tx band width of ~ 16 GHz ( BB limit)

Transmitter performance – Die Level Test

106 108 110 112 114 116 118 120 122 124 126-10

-8

-6

-4

-2

0

2

Frequency[GHz]

Po

ut [d

Bm

]

Pout VS Frequency

Measure data

Simulated data

Pout vs. Frequency

May 9, 201628

On-die Measurement (Transmit)

BPSK @13Gbps

LO @ 112.8GHz Die Probing TX Only

BPSK @14Gbps

BPSK @4Gbps

Functionality of TX verified on die level

May 9, 201629

Full Loop Measurements over the Air

Wireless interconnect block diagram with estimated path loss

Full link demonstration completed for datarate up to 6 Gbps

PKG

DiePKG

Die

PTX -1 -0.4 +10 -48 +10 -0.4 -1 = PTX-30.8dB

PA

LNA

1Gbps

Lab Setup

Module 1 Module 26 cm

BPSK @15Gbps

BPSK @6Gbps

May 9, 201630

• Low cost Electrical interconnect can be used for mmto meter at pJ/bit efficiency

• mmW transceivers will enable capacity of 100Gb/sper lane

• Low power wideband 120 GHz transceiver designedin 28nm CMOS for wireless interconnect

• High efficiency antennas on organic packagesubstrate with 38 GHz bandwidth

• Initial tests without equalization over the air fullloop interconnect achieved data-rate of 15 Gbps

Summary and Conclusions

May 9, 201631

Acknowledgment

Telesphor Kamgaing, Adel A. Elsherbini, Yuval Dafna, Tom Heller, Nitzan Oz, Sasha N. Oster, Brandon M. Rawlings, Georgios Dogiamis