c. koo millimeter-wave integrated systems lab. rf power transistors for mobile applications...

C. KOO Millimeter-wave Integrated Systems Lab.

RF Power Transistors For Mobile Applications

전기공학부 2005-21326 구찬회


Background

In general, signals with lower frequency can penetrate walls better.

But antenna size varies with RF wavelength, so low-frequency RF is not practical for handheld devices.

In addition, frequencies of RF noises are ranging from 50-2400 MHz, so frequencies > 3000 MHz is better.

History of RF Transistors• Many different types of RF transistors available: -Bipolar: Si BJTs, SiGe HBTs, III-V HBTs -FET: GaAs MESFETs, III-V HEMTs, Wide Bandgap HEMTs, Si MOSFETs


Operating Frequencies of Widely Used RF Electronics

Most RF systems having real mass markets operate under 5 GHz.

Cellular phones(GSM, CDMA) - 900MHz,1.8 and 1.9GHz

Future 3G cellular phones (CDMA2000, Wideband CDMA) - 3GHz

Advanced mobile communications - GPS(global positioning systems) - 1.8GHz- GPRS(general packet radio service) - 2.5GHz

Wireless local area network (Bluetooth) - 2.4 GHz

Collision avoidance radar used in automobiles - 77 GHz

Microwave oven - 2.4 GHz


RF Transistor Figures of Merit

Cutoff Frequency fT

Frequency at which the magnitude of the short circuit current gain h21 rolls off to 1 (0 dB).

Max Frequency of Oscillation fmax

Frequency at which the unilateral power gain U rolls off to 1 (0 dB).

fT and fmax can be extracted from h21 and U roll off at higher frequencies at a slope of –20 dB/dec.

• Further RF Transistor FOMs : NFmin, Pout, PAE, MAG


HBT (1)


HBT (2)

HBT Types• GaAs HBT• InP HBT• SiGe HBT

Design Features• Wide bandgap emitter• Narrow bandgap base• Thin base (less than 0.1 μm)• High base doping

• GaAs-based HBT has been the most widely used HBT in RF design, but SiGe HBT has gained popularity recently due to its superior noise performance and its compatibility with existing Si CMOS technology.


HEMT (1)

HEMT: High Electron Mobility Transistor


HEMT (2)

Design Features• Deep sub-µm gate• Mushroom gate• Very short gate length• High mobility channel layer• Large conduction band offset 2DEG

HEMT Types• AlGaAs/GaAs HEMT• InP HEMT• AlGaN/GaN HEMT

• Importance of metamorphic HEMT (mHEMT) will continue to grow. -The key feature of this device is an InGaAs layer grown on GaAs substrate with an In content higher than that in GaAs pHEMT. -The main advantge of this approach is inexpensive GaAs substrate can be used to obtain InP HEMT like performance.


Power Amplifiers for Mobile Communication Systems (1)

Cellular PA-Current PA : 95% with GaAs-New Comers : SiGe PA & CMOS PA (skeptical)-SiGe BICMOS : better for integration better for cost (?) (Triquint claimed that GaAs has 15% less cost)-Issues : SoC or SoP

Wireless LAN-Competitive technologies same with cellular PA-IEEE 802.11g(2.4GHz, 54Mbps) & IEEE 802.11a(5GHz, 54Mbps)-67% of 177M PAs from GaAs in 2008 (Strategy Analytics)

Cellular Base Stations-90% market with LDMOS-Competitive Technologies : GaN HFET(reliability), GaAs PHEMT

Switch – mainly with GaAs PHEMT


Power Amplifiers for Mobile Communication Systems (2)

• Technologies for GaN HEMTs are not yet mature, but devices with fT and fmax exceeding 100 GHz and very high output power densities have been demonstrated.

• Wide bandgap FETs(SiC MESFET& GaN HEMT) show the highest output power densities of all RF FETs in the frequency range important for currentmobile communication sytems (up to 5 GHz)


Trend of RF Transistors

Important Trends

• Continuous increase of the frequency limits, i.e. fT and fmax

• Development of low- cost RF transistors for mass onsumer markets

“InP HBT and HMET possess the best frequency performance”But, the technology for InP-based devices is not yet mature. These devices alsohave poorer power performance.


References

RF and Microwave Power Amplifier and Transmitter Technologies- Frederick H. Raab, Peter Asbeck, Steve Cripps, Peter B. Kenington, Zoya B. Popovic, Nick Pothecary, John F. Sevic and Nathan O. Sokal

F. Schwierz and J. J. Liou, Modern Microwave Transistors – Theory, Design, and Applications, J. Wiley 2002

L. D. Nguyen et al., Ultra-High-Speed Modulation-Doped Field-Effect Transistors,Proc. IEEE, 80, p. 494.

D. Halchin, M. Golio, Trends for Portable Wireless Applications, Microwave J., Jan. 1997, p. 62

F. Schwierz and J. J. Liou, Semiconductor Devices for RF Applications: Evolution and Current Status, Microel. Rel. 2000.

c. koo millimeter-wave integrated systems lab. rf power transistors for mobile applications...

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