beyond 10 gbit/s mm-wave wireless communication using … · mimo and dual polarization / xpic next...

Beyond 10 Gbit/s mm-Wave Wireless Communication using

SiGe BiCMOS Transceivers

Erik Öjefors1) and Mats Alexanderson2) 1) Sivers IMA AB, 2) Trebax AB

[email protected]

WS12: EuMIC - SiGe for mm-Wave and THz

SiGe for mm-Wave and THz 2 September 6, 2015

Outline

• Introduction • System overview of Point-to-Point mm-wave

radio • 240-GHz Communication in Dotseven • Components for 10 Gbit/s PtP radios

• E-band LNAs • E-band PAs

• Conclusions


Introduction

• 4G/5G cellular networks need high backhaul capacity between the base

stations and core network – fiber not always an option

• mm-wave transceivers key component for Point-to-Point backhaul radio

• Unlicensed V-band (60 GHz) for short distances • E-band (71-76 GHz/81-86 GHz) for medium range • Future mm-wave bands 120/160/240 GHz offer

even larger short-range capacity


System Overview

Full-duplex FDD (separate TX, RX, external diplexer) telecom grade

Switch from III-V MMICs to custom integrated Si/SiGe ICs

LNA and PA critical blocks: RX NF < 8 dB, TX Psat > 20 dBm

The mm-Wave Transceiver – E-band Example

Antenna

71-76 GHz

81-86 GHz

Diplexer Freq. Conv

LNA

PA

RX I/Q

xn

LO

TX I/Q

xn

LO


System Overview

E-band licensed in 250-MHz channels, bonding of multiple channels

Single-carrier due to line-of-sight, BPSK up to 256QAM typical modulations

Up to 10 Gbit/s in 2-GHz channels provided by commercial modems

MIMO and dual polarization / XPIC next steps for > 10 Gbit/s rates

Point-to-Point mmWave Modems

71 GHz

Q

250 MHz channel raster

Channel bonding

Example: 71-76 GHz duplex band

76 GHz

I

Constellation 16 QAM


240GHz Communication Demonstration

6

1st generation 240-GHz Dotseven TX and RX from

University of Wuppertal, connected to radio modem.

● Center frequency 240GHz

● Dual polarized chip versions,

one polarization used for

measurement

● Driven by BCM85100

wideband 10Gb/s modem

test system

● Double up/down-conversion

with 2GHz IF

Measurement performed at Trebax AB, Gothenburg, Sweden on June 15, 2015



7

Throughput results

Signal bandwidth

250MHz 2000MHz

Symbol rate 222Mbaud 1595Mbaud

Modulation 64QAM QPSK

Net bit rate 1015Mbit/s 2726Mbit/s

MSE 26.5dB 14.7dB

BER < 1E-11 Not measured*

* Symbol rate too fast for BERT application to work without clock reconfiguration.

with constellation diagrams at receiver



8

Main limitations for higher throughput

Adaptive equalizer response for freq=240GHz, B=2000MHz. QPSK with 2726Mbit/s.

● Transmitter linearity and

eventually also phase noise limits

use of higher modulation order

● Receiver noise limits SNR at

wide channels

● Group delay and amplitude

distortion grows for wide

channels

● Next generation Dotseven chip

set with improved module design

targets increase to 10Gb/s


Components for E-band radio

The mm-Wave TRX – Present Solution

SiGe Upconverter GaAs PA

Waveguide

TX module

TX RX

IF

LO

TX compression 71-76 GHz

Psat = 20 dBm at

Waveguide port

NF ≈ 6.5 dB

TX

SiGe RX Gain / NF Performance

LNA SiGe RX Chip

Gain > 20 dB

Dotseven target: Replace GaAs PA Improve SiGe LNA


E-band LNA in Dotseven Tech.

10 10

Common-emitter HBT simplified noise model – fmax and NF

NF minimized by improving ft and minimizing Rb (and Re) of the device.

Better signal-to-shot-noise ratio at the collector node with higher ft

Lower Rb minimizes Vbn, and lets us reduce Zs

Re(Zs) = Ropt, best compromise between noise from Vbn and Ibn.

Problem: Re(Zopt) ≠ Re(Zin), noise match yields poor return loss!

Inductive emitter degeneration typically used for simultaneous matching.

IbnZSZS

Vbn Rb

Icn ZLZL

B

E

C



11 11 11

Implemented LNA Design in IHP SG13G2 Tech

• ESD protection shunt stub at input • Input series inductance replaced by stub • Real part of impedance levels retuned with stub • Emitter degeneration by interconnects • Wide-band transformer output match • (8 x 0.96 x 0.12) mm2 devices biased at IC = 7 mA

Input Output

xfmr

RF In

RF In

VB

Q1

Rbias

VCC

2:1

xfmr

ESDTL Stub

Ibias

RF Out

Q2

Input

stub

320 um

30

0 u

m



12 12

Single-Stage LNA S-Parameters in IHP SG13G2

12

f (GHz)

S-p

ara

m (

dB

) S22

S21

S21

S11



13 13

NF Results – Two-Stage Cascaded E-Band LNA

0

1

2

3

4

5

6

65 70 75 80 85 90

NF

[dB

]

Freq. [GHz]

Meas [dB]

Sim [dB]

Simulation and measurements in good agreement Target NF < 4 dB (Commercial E-band GaAs LNA: NF = 3-5 dB)

Two-stage LNA


E-band PA in Dotseven Tech.

14

SiGe Upconverter GaAs PA

Waveguide

TX module IF

LO

TX compression 71-76 GHz

Psat = 20-23 dBm at

Waveguide port

TX

Goal Replace GaAs PA

14

E-band transceiver – Power Amplifier

PA critical, TX PSAT > 20 dBm, OIP3 > 25 dBm typical requirements for high-order modulation



15

mm-Wave Power-Amplifier Design Strategies

15

Large-Device Design for >20 dBm Output Power

Power-Combining

● Limited voltage swing – high ac current

● Large or multiple parallel power devices

needed

● Low load impedance – transformation

losses, distributed parasitics

● Potential electro-thermal stability issues

● Modular approach, small transistor cells

● Good dc stability, individually biased

amplifiers

● Space-consuming design, less heat

concentration

● Power-combining losses

Zload

<< 50

Zload

Co

mb

ine

r



16

Microstrip Combining Network

● Electrially short network, mainly

current combining

● Equal excitation assumed

● Zsrc = 100 simplifies design

● C = 40 fF provides matching

● EM-simulated IL = 0.7-1.1 dB (71-

86 GHz)

ZLoad

50

Zsrc

100

C

Output

VCC rail

M1-M3

GND Si

Strip 6 um

6 um



17

Power-Amplifier Unit Cell

VB

RF In T1

Q1

Q3

Q2

Q4

VCC

T2 RF Out

Simplified Schematic

T1 T2

VCC

VCC

Out In

Layout

Zload = 50 // Lleakage,T2

17

Differential cascode

• Q1-Q4: (16 x 0.96 x 0.12) um2,

biased at ICQ = 20 mA

• VCC = 3.3V, (VB = 2.2 V

internally biased)

• Current-summing combining

req. high unit cell impedance

• T1 2:1 ratio, Zin = 100

• T2 1:1 ratio, Zload = 100



18

Power Sweep 71-.86 GHz of a 8-way Combined Amplifier

● Low-band Psat =

22 dBm, 2-3 dB

roll-off at in the

81-86 GHz band

● PAE = 8.4% @

76GHz

● OIP3 25 dBm in

lower band

Meas Psat: 22 dBm @

76 GHz, sim: 24 dBm


Conclusions

• Demand for fixed mm-wave point-to-point radio driven by need for backhaul in 4G networks

• 256 QAM deployed in 2 GHz channels enable 10-Gb/s full duplex with commercial modems

• MIMO and/or dual-polarization with XPIC will let E/V-band fixed radio evolve beyond 10 GBit/s

• PAs and LNAs critical blocks for overall link budget – SiGe is catching up with III-V


Acknowledgements

This work is part of the DOTSEVEN project supported by the European Commission through the Seventh Framework Program for Research and Technological Development. The authors would like to thank N. Sarmah and Prof. U.R. Pfeiffer, University of Wuppertal for providing the 240 GHz TX/RX testbed. Dr B. Heinemann and Dr. H. Rücker, IHP GmbH, are acknowledged for the SiGe HBT technology support.

beyond 10 gbit/s mm-wave wireless communication using … · mimo and dual polarization / xpic next...

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