Cellular Antenna Switches for Multimode Applications Based on a Silicon-On-Insulator (S-O-I) Technology

Transcription

1 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

2 Outline 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

3 Handset Shipments by Mobile Standard 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.

4 3G/4G Front End Architectures GSM RX1 GSM RX2 GSM RX3 RX SAW Filters Switch Duplexer Module SP9T Switch GSM RX4 UMTS1 TX UMTS2 TX UMTS3 TX UMTS3 RX Duplexer 2 Duplexer 1 Duplexer 3 GSM TX Filters Control Lines UMTS2 RX GSM 850/900 UMTS1 RX GSM 1800/1900 3G / 4G system architectures require a complex integration of switch, filter, and duplex functions in the front-end.

5 Cellular Switch Requirements 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 PA LNANA ANT V pp

6 Thick and Thin Film SOI 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 S S G D B D B n+ n+ p+ n+ n+ p+ S PWELL ~1000 Ohm-cm Si substrate S G D n+ n+ G Deep Trench S G D PWELL BURIED OXIDE (~ 1 um) G B D G D S n+ n+ BURIED OXIDE (~ 1 um) ~1000 Ohm-cm Si substrate Shallow Trench Shallow Trench G D S n+ n+ B B ~ 1.5 um ~ 0.2 um

7 Switch Technology Figure of Merit Process Device Ron [Ω-mm] Coff [ff/mm] Ron*Coff [fs] 0.18um thick-film SOI 0.18um thin-film SOI 5V NFET Lg=0.6um 13.0nm gate ox 2.5V NFET Lg=0.32um 5.2nm gate ox um SOS 0.25um SOS NFET 10.0nm gate ox NFET 5.0nm gate ox phemt Single gate um thin-film SOI offers Ron*Coff similar to GaAs phemt. Integrated switch controller in the SOI die.

8 Switch Branch Data Parameter Unit SOI phemt Insertion Loss (2GHz) db Isolation (2GHz) db Ron Ohms Coff ff Ron*Coff fs 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.

9 SOI SP9T Switch for SDMA Applications TX2 TX1 TRX3 Control Pins TRX2 ANT TRX1 RX4 RX3 RX2 RX1 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

10 SP9T Insertion / Return Loss Measured Insertion Loss, db Frequency, GHz TX2 TX1 TRX3 TRX2 TRX1 RX1 RX2 RX3 RX4 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 5 TX2 about 0.2 / 0.25 db. Measured Return Loss, db Frequency, GHz TX1 TRX3 TRX2 TRX1 RX1 RX2 RX3 RX4 No intentional matching employed. Less insertion loss achievable with matching.

11 Tx/TRX to RX Isolation db 915 MHz 1990 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.

12 TX / TRX to TX / TRX Isolation db 915 MHz 1990 MHz 2170 MHz 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.

13 RX to RX Isolation db 915 MHz 1990 MHz 2170 MHz 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.

14 High Resistivity Silicon Substrate Linearity 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.

15 Harmonic Distortion Low Band Harmonics, dbm High Band Harmonics, dbm MHz 1780 MHz 2fo 3fo 3fo 2fo 2fo Input Power, dbm TX1_2fo TX1_3fo TRX1_2fo TRX1_3fo TX1_2fo TX1_3fo TRX1_2fo TRX1_3fo 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. Input Power, dbm

16 SP9T Power Handling SP9T high power branches tested for breakdown. VSWR=3:1 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

17 Intermodulation Distortion * T. Ranta et. al., 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. TX Frequency (F1), MHz Blocker Frequency (F2), MHz Distortion Type IMD (RX) Frequency, MHz Measured TRX IMD, dbm Switch SDM F1 F F2 F F1+F F1 F F2 F F1+F

18 Spurious Emissions RBW=30 khz VBW=500 khz Spurious Level, dbm -100Offset -17 db SWP 50 of Frequency, GHz 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.

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

20 Do You Have Any Questions?