Cellular Antenna Switches for Multimode Applications Based on a Silicon-On-Insulator (S-O-I) Technology Ali Tombak, Christian Iversen, Jean-Blaise Pierres, Dan Kerr, Mike Carroll, Phil Mason, Eddie Spears and Todd Cillenwater

• Motivation

• Silicon-on-Insulator (SOI) for Antenna Switches

• Design of High Order Switches on SOI

• Small Signal Measurements

• Harmonics and IMD Performance

• Spurious Emissions

• Summary and Conclusions

Outline

• Ever increasing need for higher data rates drives the standards to those of 3G / 4G.

• Market share and volume of 3G / 4G handsets expected to increase tremendously.

• Many bands and band combinations considered for 3G / 4G handsets to roam at different regions.

Handset Shipments by Mobile Standard

• 3G / 4G system architectures require a complex integration of switch, filter, and duplex functions in the front-end.

GSM RX1

GSM RX2

GSM RX3

GSM RX4

GSM 1800/1900

GSM 850/900

UMTS1 TX

UMTS2 TX

UMTS3 TX

UMTS3 RX

UMTS2 RX

UMTS1 RX

Duplexer 2

Duplexer 3

Duplexer 1

RX SAW FiltersSP9T Switch

GSM TX Filters

Control Lines

3G/4G Front End Architectures

Switch Duplexer Module

• PA output power often represented by ~36 dBm source

• Antenna port impedance varies greatly • Operating VSWR up to 5:1, functional

into 20:1

• Off-state switch must stand-off high AC voltages• Maintain Reliability• Linearity

• For most IC technologies, several FETs must be stacked in series

• High resistivity substrate decouples FET body terminals, enabling stacking

40-80 Vpp

PA

LNANA

ANT

Cellular Switch Requirements

• Thick-film SOI• Device layer thickness > S/D junction

depth• Device operation similar to bulk Si• Circuit blocks can be transferred from

bulk Si with minimal changes

• Thin-film SOI• S/D doping extends to buried oxide

reduced S/D capacitance (Coff)• More extensive re-design needed for

existing circuit blocks

DS

B

~ 1.5 um

BG

DS

~1000 Ohm-cm Si substrate

PWELL

BG

DS

PWELLn+ n+ p+ n+ n+ p+

BURIED OXIDE (~ 1 um)

Deep Trench Shallow Trench

G

DSB

~ 0.2 um

G DS

~1000 Ohm-cm Si substrate

n+ n+

Shallow Trench

G DSn+ n+

G DSn+ n+

BURIED OXIDE (~ 1 um)

Thick and Thin – Film SOI

B

G

Process Device Ron [Ω-mm] Coff [fF/mm] Ron*Coff [fs]

0.18um thick-film SOI5V NFETLg=0.6um

13.0nm gate ox1.9 255 485

0.18um thin-film SOI2.5V NFETLg=0.32um

5.2nm gate ox0.8 310 250

0.5um SOS NFET10.0nm gate ox 2.8 270 756

0.25um SOS NFET5.0nm gate ox 1.6 280 448

pHEMT Single gate 1.4 160 224

• 0.18um thin-film SOI offers Ron*Coff similar to GaAs pHEMT.

• Integrated switch controller in the SOI die.

Switch Technology Figure of Merit

Switch Branch Data

• NFET switch branch, 0.18 um thin-film SOI.

• Common gate series stack of NFETs.

• SOI requires larger FET stack number, but switch branch is very compact due to 0.18 um BEOL design rules.

Parameter Unit SOI pHEMT

Insertion Loss (2GHz) dB 0.34 0.24

Isolation (2GHz) dB 20.2 15.0

Ron Ohms 2.7 1.9

Coff fF 92 147

Ron*Coff fs 250 280

TRX2

TX1 TRX3TX2

RX3RX4 RX2 RX1

TRX1

ANT

Control Pins

• Wire bond and flip chip SOI SP9T switches designed for an SDM application.• 2 high power GSM TX,

• 3 high power WCDMA, and

• 4 low power GSM RX ports

SOI SP9T Switch for SDMA Applications

• At 915 MHz,

• TX and TRX ports have 0.45 dB,

• RX ports have 0.55 dB insertion loss.

• At 1990 and 2170 MHz, insertion losses increase by about 0.2 / 0.25 dB.

• No intentional matching employed. Less insertion loss achievable with matching.

‐1.4‐1.3‐1.2‐1.1‐1

‐0.9‐0.8‐0.7‐0.6‐0.5‐0.4

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Frequency, GHz

TX2TX1TRX3TRX2TRX1RX1RX2RX3RX4

‐30

‐25

‐20

‐15

‐10

‐5

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Frequency, GHz

TX2TX1TRX3TRX2TRX1RX1RX2RX3RX4

Mea

sure

d In

serti

on L

oss,

dB

Mea

sure

d R

etur

n Lo

ss, d

B

SP9T Insertion / Return Loss

dB 1990 MHz915 MHz 2170 MHz

• TX / TRX to RX isolation better than 32 dB up to 2170 MHz.

• Adjacent TRX / RX and closer RX / ANT combination achieve lower isolation compared to the rest due to higher branch-to-branch and bond wire coupling.

• Higher isolation achievable with flip-chip SP9T.

Tx/TRX to RX Isolation

1990 MHz915 MHz 2170 MHzdB

• TX / TRX to TX / TRX isolation better than 29 dB up to 2170 MHz.

• Lower isolation to one branch due to higher branch-to-antenna and bond wire coupling. Other combinations achieve better than 34 dB isolation up to 2170 MHz.

• Higher isolation achievable with flip-chip SP9T.

TX / TRX to TX / TRX Isolation

1990 MHz915 MHz 2170 MHzdB

• RX to RX isolation better than 28 dB up to 2170 MHz.

• Adjacent branches achieve lower isolation compared to other combinations due to higher branch-to-branch and bond wire coupling.

• Higher isolation achievable with flip-chip SP9T.

RX to RX Isolation

• A parasitic conduction layer may form at Si/SiO2 interface below SOI buried oxide.

• A structure (metal trace or device) above the oxide with varying potential may modulate the conductive characteristic at the interface, creating a nonlinear impedance.

• This limited the linearity of SOI switches, but this issue has been solved now, making SOI a viable high power switch technology.

C. Roda Neve, D. Lederer, G. Pailloncy, D. C. Kerr, J. M. Gering, T. G. McKay, M. S. Carroll and J.-P. Raskin, “Impact of Si substrate resistivity on the non-linear behaviour of RF CPW transmission lines”, Proceedings of the 3rd European Microwave Integrated Circuits Conference, October 2008, Amsterdam, The Netherlands.

High Resistivity Silicon Substrate Linearity

900 MHz

1780 MHz

• Low Band 2fo and 3fo better than -58 and -47 dBm up to 37 dBm input power, respectively.

• High Band 2fo and 3fo better than -49 and -46 dBm up to 36 dBm input power, respectively.

• Measured harmonic levels considerably better than most antenna/mode switch specifications.

2fo

3fo

2fo

‐90‐85‐80‐75‐70‐65‐60‐55‐50‐45‐40

20 22 24 26 28 30 32 34 36 38

Input Power, dBm

TX1_2foTX1_3foTRX1_2foTRX1_3fo

‐90‐85‐80‐75‐70‐65‐60‐55‐50‐45‐40

20 22 24 26 28 30 32 34 36 38

Input Power, dBm

TX1_2fo

TX1_3fo

TRX1_2fo

TRX1_3fo

Low

Ban

d H

arm

onic

s, d

Bm

3fo

2fo

Hig

h B

and

Har

mon

ics,

dB

m

Harmonic Distortion

• SP9T high power branches tested for breakdown.

• No measurable degradation in insertion loss and harmonics observed up to 37.5 dBm with VSWR = 3:1 at LB.

VSWR=3:1

VSWR=3:1

VSWR=3:1

SP9T Power Handling

* T. Ranta et. al., 2005.

TX Frequency (F1), MHz

Blocker Frequency (F2), MHz

Distortion Type

IMD (RX) Frequency,

MHz

Measured TRX IMD, dBm

Switch SDM

1950 1760 2F1‐F2 2140 ‐119 ‐117

1950 4090 F2‐F1 2140 ‐110 ‐108

1950 190 F1+F2 2140 ‐106 ‐111

836.5 791.5 2F1‐F2 881.5 ‐122 ‐117

836.5 1718 F2‐F1 881.5 ‐120 ‐115

836.5 45 F1+F2 881.5 ‐102 ‐118

• Typical IMD specification is -105 dBm.

• Adequate IMD levels measured for the UMTS ports.

• IMD 45 / IMD 190 improved significantly with the shunt ESD inductor on the SDM.

Intermodulation Distortion

RBW=30 kHz

VBW=500 kHz

‐150‐145‐140‐135‐130‐125‐120‐115‐110‐105‐100

0.8

0.82

0.84

0.86

0.88 0.9

0.92

0.94

0.96

0.98 1

Spurious Level, dBm

Frequency, GHz

Offset -17 dB0

-150

-145

-140

-135

-130

-125

-120

-115

-110

-105

-100

SWP 50 of 50

• Measured RX mode spurious emissions better than -123 dBm.

• Measured RX band noise better than -97 dBm with fTX = 915 MHz and PTX = 35 dBm.

Spurious Emissions

• 3G / 4G smart handsets will dominate the market in the next few years, presenting a great opportunity for front-end suppliers.

• High resistivity SOI enables FET stacking, allowing the design of high power antenna / mode switches.

• Low RON*COFF product results in competitive switch insertion loss and isolation performance.

• High resistivity SOI substrate linearity issues solved, enabling the design of high throw count SOI antenna switches with excellent harmonic and intermodulation distortion performance.

• Adequate levels of TX and RX mode spurious emissions measured.

• 2000 V Human Body Model (HBM) ESD tolerance achieved on the RF ports (no blocking capacitors used on ports).

Conclusion

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