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Linearity of HBTs for RF power application

2002-21535 배 성 준

Outline

1. Linearity in PA2. Intercept points, Volterra analysis3. Volterra analysis – Maas4. Volterra analysis – Pavlidis5. Volterra analysis – Asbeck6. Volterra analysis – Bumman Kim7. Others8. Conclusion

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Linearity in PA

Y=a1X+a2X2+a3X3+….. BPF rejection

Intermodulation ProductHard to remove specification of PA

PA

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Intercept points

Pin

fundamentalIM3

IM5

IP3

IP5

Intercept points : linear parameters, small signal linearity

The difference between fundamental and IM : large signal linearity

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Volterra analysis

Volterra series analysis is more general methods than power series analysis,is standard method to analysis weekly nonlinear circuits,is limited only at small signal levels,but gives inspection of intermodulation mechanism at large signal level.

Detailed descriptions for Volterra series : S. A. Maas, Nonlinear Microwave Circuits, Norwood, MA: Artech House, 1988

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depletion cap is dominant at forward bias

= zero

3 nonlinearities : resistive junction, capacitive junction, nonlinear current source

Volterra analysis – Maas

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4 nonlinearities : resistive junction(gje), capacitive junction(Cje), nonlinear current source(), Cbc

Volterra analysis – Pavlidis

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Partial cancellation of and gje

210

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Longer collector : degraded small signal linearity, but not degraded large signal linearity.

Vce=2.7V

Wc=4000A

Volterra analysis – Asbeck

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gm Cbc

A : gm

B : Ic dependence of the collector depletion layerC : Kirk effect

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No Kirk effect

Nonlinear Cbc

Linear Cbc

NonlinearNonlinear

+linearNormal

Punch-though

Linear

Volterra analysis – Bumman Kim

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Self-linearization

Large Signal Linearization !!

Others – input matching vs. linearity

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Others - IMD Asymmetry

-75-70-65-60-55-50-45-40-35-30-25-20

0 5 10 15 20 25 30

Pout(dBm)

IMD

IMD3_HIMD3_L

Memory effect at Envelope frequency.

1.Base band termination ( imaginary )2.Thermal resistance

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Conclusion

High IP3 of HBTs ( good LFOM ) Partial cancellation of emitter and collector current nonlinearities The negative feedback from RE, RB linearization Improved IP3 with punch-through, thin collector structures Thin collector structure results low Bvceo The epi-structures for GSM, CDMA may be different.

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References

[1] Maas, S.A., Nelson, B.L., Tait, D.L., “Intermodulation in heterojunction bipolar transistors,” Microwave Theory and Techniques, IEEE Transactions on , Volume: 40 , Issue: 3 , March 1992, Pages:442 – 448

[2] Samelis, A., Pavlidis, D., “Mechanisms determining third order intermodulation distortion in AlGaAs/GaAs heterojunction bipolar transistors,” Microwave Theory and Techniques, IEEE Transactions on , Volume: 40 , Issue: 12 , Dec. 1992 Pages:2374 - 2380

[3] Nan Lei Wang, Wu Jing Ho, Higgins, J.A., “AlGaAs/GaAs HBT linearity characteristics,” Microwave Theory and Techniques, IEEE Transactions on , Volume: 42 , Issue: 10 , Oct. 1994, Pages:1845 – 1850

[4] Lu, K., McIntosh, P.M., Snowden, C.M., Pollard, R.D., “Low-frequency dispersion and its influence on the intermodulation performance of AlGaAs/GaAs HBTs,” Microwave Symposium Digest, 1996., IEEE MTT-S International , Volume: 3 , 17-21 June 1996 Pages:1373 - 1376 vol.3

[5] Iwai, T., Ohara, S., Yamada, H., Yamaguchi, Y., Imanishi, K., Jeshin, K., “High efficiency and high linearity InGaP/GaAs HBT power amplifiers: matching techniques of source and load impedance to improve phase distortion and linearity,” Electron Devices,IEEE Transactions on , Volume: 45 , Issue: 6 , June 1998 Pages:1196 - 1200

[6] Iwamoto, M., Asbeck, P.M., Low, T.S., Hutchinson, C.P., Scott, J.B., Cognata, A., Xiaohui Qin, Camnitz, L.H., D'Avanzo, D.C., “Linearity characteristics of GaAs HBTs and the influence of collector design,” Microwave Theory and Techniques, IEEE Transactions on , Volume: 48 , Issue: 12 , Dec. 2000 Pages:2377 - 2388

[7] Woonyun Kim, Sanghoon Kang, Kyungho Lee, Minchul Chung, Youngoo Yang, Bumman Kim, “The effects of Cbc on the linearity of AlGaAs/GaAs power HBTs,” Microwave Theory and Techniques, IEEE Transactions on , Volume: 49 , Issue: 7 , July 2001 Pages:1270 - 1276