an empirical large signal model for rf ldmosfet transistors

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME

International Conference on Communication Systems (ICCS-2013) October 18-20, 2013 B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India

An Empirical Large Signal Model for RF LDMOSFET Transistors

M Tamoum1, R Allam2, J M Paillot2

1Université de Jijel, Jijel, Algeria 2CNRS-XLIM, UMR 7252, Université de Poitiers, Angoulême (France)

[email protected], [email protected], [email protected]

ABSTRACT: An accurate and simple large-signal RF model of discrete LDMOSFET transistors is presented. This empirical model is used for analysis and design of microwave power amplifiers. The interpolation of the measured data, using polynomial expressions, provides a description of the LDMOSFET’s nonlinearities in CAD software. The LDMOSFET transistor used is a BLF2043F (NXP Semiconductors). A 2.5-GHz 10-W class AB power amplifier was designed and implemented to validate our large-signal model. The measured and simulated power amplifier characteristics match very well. KEYWORDS: LDMOSFET Transistors, Non-linear Modeling, Microwave Power Amplifiers, Simulation, Circuit Analysis

I. INTRODUCTION LDMOSFET Transistor components are widely used for power amplifiers at base stations and relay systems for wireless communications. It has the advantage of combining high voltage capability and very linear microwave power amplification. In order to develop a circuit application for this component, it is necessary to havean accurate device large-signal model for efficient intensive CAD. Different empirical models have been developed by many authors for the analysis and design of high power amplifiers [1-3]. Here, we propose a simple and accurate large signal model based on the microwave measures for analysis and design of RF LDMOSFET power amplifiers. Our model is based on the experimental values of the dynamic parameters measured in the RF range. The Dambrine [4] procedure is used to determine the transconductance, output conductance and gate-to-source capacitance at different biasing conditions. These elements are extracted from the S parameters measured in the frequency range 0.2-2.7 GHz. Then, they are used to construct the large-signal model. LDMOSFET transistors are generally encapsulated in a standard power microwave package. The package parameters measurement is made only by removing the semiconductor chip. We have measured these package parameters [5]. In order to verifythe validity of this method, a large-signal model of the LDMOSFET has been constructed and implemented in commercial harmonic balance software (ADS). Finally, a 2.5-GHz

INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)

ISSN 0976 – 6464(Print) ISSN 0976 – 6472(Online) Special Issue (November, 2013), pp. 01-07 © IAEME: www.iaeme.com/ijecet.asp Journal Impact Factor (2013): 5.8896 (Calculated by GISI) www.jifactor.com

IJECET © I A E M E



10-W class AB amplifier is designed and implemented. The measured output power, gain and efficiency are compared with the simulated ones, and are found to be in good agreement. II. LARGE SIGNAL MODEL

The large-signal model is directly derived from the microwave small signal equivalent circuit and takes into account the main nonlinearities: The drain current generator IDS (transconductance Gm and output conductance GD) and the gate-to-source capacitance CGS. The other circuit elements are assumed to be linear. The equivalent circuit of the LDMOSFET is shown in Fig. 1.

Fig. 1: Small-signal LDMOSFET equivalent circuit

Most conventional large signal characterizations are based on DC measurements of the drain current IDS. This method is not satisfactory because thermal and trap effects may modify the microwave behaviour of the LDMOSFET. The profile of the non-linear transconductance versus gate-to-source voltage VGS is the dominant factor in amplification process. The output power of RF PA follows this profile. The gate-to-source capacitance CGS has a secondary importance on power amplifier performance, compared to the transconductance. For this, the gate-to-source capacitance is assumed to depend exclusively on VGS [6]. The drain current function is:

))(,(),( 000 DSDSDSGSd

V

VGSDSGSmDS VVVVGdVVVGI

GS

TH

(1)

Where: VGS: internal gate voltage VDS: internal drain voltage VDS0: quiescent internal drain voltage VTH: threshold gate voltage

Gm(VGS,VDS0), Gd(VGS,VDS0) are the RF transconductance and RF conductance determined from the LDMOSFET measurements. They are described by using polynomial expressions.The polynomial order is chosen to give the best fit with the measured values:

)(..),(0

GSP

GS

n

ppDSoGSm VFVaVVG

(2)

F(VGS) is a function used to cancel the polynomial ripples. The gate charge is modeled by:



GS

TH

V

VGSGSDSoGSGSGS VKdVVVCQ .),( (3)

With:

)(..),(0

GS

n

p

PGSpDSoGSGS VFVbVVC

(4)

CGS(VGS,VDSo) is the capacitance determined from the non-linear characterization of the LDMOSFET transistor, K corresponds to the value of this capacitance below threshold voltage. Comparisons between the measured and the interpolated transconductance (Fig. 2), conductance (Fig. 3) and gate-source capacitance (Fig. 4) are shown. Good fit is observed.

0 1 2 3 4 5 6 7 80

100

200

300

400

500

600

700

Tran

scon

duct

ance

, Gm (m

S)

Gate-Source Voltage, Vgs (V)

Measure Interpolation

Fig. 2: Comparison between measured and interpolated transconductance

0 1 2 3 4 5 6 7 80

1

2

3

4

5

6

7

Dra

in C

ondu

ctan

ce, G

d (m

S)



Fig. 3: Comparison between measured and interpolated conductance



0 2 4 6 80

5

10

15

20

25

Gat

e-S

ourc

e C

apac

itanc

e, C

gs (p

F)



Fig. 4: Comparison between measured and interpolated gate-source capacitance

III. VALIDATION OF LARGE MODEL To validate our work, the model has been implemented using harmonic balance of the ADS simulator. The design, the implementation and performances test of a 2.5 GHz 10-W RF class AB power amplifier were made. The transistor was placed in the specific cell with a heat sink (Fig.5). A LDMOSFET BLF2043F (NXP Semiconductors) was chosen. Simulation results are presented and compared to the measured data in Fig. 6, 7, 8 and 9.

Fig. 5: Realized power amplifier photo



0 5 10 15 20 25 300

10

20

30

40

Out

put P

ower

, Pou

t (dB

m)

Input Power, Pin (dBm)

Measure Simulation

Fig. 6: Comparison between measured and simulated output power

0 5 10 15 20 25 300

4

8

12

16

20

Pow

er G

ain,

Gp

(dB

)


Measure Simulation

Fig. 7: Comparison between measured and simulated power gain

0 5 10 15 20 25 300

20

40

60

80

100

Effic

ienc

y (%

)


Measure Simulation

Fig. 8: Comparison between measured and simulated efficiency



0 5 10 15 20 25 300

400

800

1200

1600D

rain

-Sou

rce

Cur

rent

, Ids

(mA

)


Measure Simulation

Fig. 9: Comparison between measured and simulated DC drain current

Our model doesn't take in consideration the thermal effects, however, the comparison between simulation and measure is satisfactory. This work allows the designer to quickly predict the LDMOSFET RF power amplifier performances. Results of measure are also in good agreement with those given by the manufacturer of the transistor [7]. IV. CONCLUSION An accurate and simple large-signal model for LDMOS transistor has been presented. It was implemented by using the ADS simulator for its validation by the realization of an RF power amplifier. The accuracy of the model has been verified by the good agreement between the measured and simulated performances, and hence, can be added to the ADS library. REFERENCES [1] M. Miller, T. Dinh, and E. Shumate, “A new empirical large signal model for silicon RF LDMOSFET ,” in IEEE MTT-S Int. Microw. Symp.Dig., Vancouver, BC, Canada, pp. 19-22, 1997. [2] Y. Yang, J. Yi, and B. Kim, “Accurate RF large signal model of LDMOSFET’s including self-heating effect,” IEEE Trans. Microwave Theory & Tech., vol. 49, no. 2, pp. 387-390, February 2001. [3] H. Nemati, C. Fager, M. Thorsell, and H. Zirath, “High-efficiency LDMOS power amplifier design at 1GHz using optimized transistor model,” IEEE Trans. Microwave Theory & Tech., vol. 57, no. 7, pp. 167-1654, July 2009. [4] G. Dambrine, A. Cappy, F. Heliodore and E. Playez, “A new method for determining the FET small-signal equivalent circuit,” IEEE Trans. Microwave Theory and Tech., vol. 36, n° 7, pp. 1151-1159, July 1988. [5] M. Tamoum, R. Allam& F. Djahli, “Accurate Large-Signal Characterization of LDMOSFET Transistor in Package”, Microwave and Optical Technology Letters, Vol. 53, No. 3, March 2011. [6] S.C Cripps, “Advanced Techniques in RF amplifier design”, Artech House, 2002. [7] Philips, “BLF2043F UHF Power LDMOS Transistor”, Philips Semiconductors Data Sheet, Mars 2002.



BIOGRAPHY

Mohammed TAMOUM was born in Jijel, Algeria, in 1972. He received degrees of Engineer, Magistère, and Doctorate, all in electronics engineering from Setif University, Algeria, in 1995, 2001, and 2013, respectively. He is currently working as a lecturer at Jijel University, Algeria. Since 2006 he co-operated on a research project with the University of Poitiers, France. His research interests are RF MOSFET’s modeling and characterization, lately with a larger emphasis in LDMOSFET RF modeling and simulation.

Rachid ALLAM (M’93-SM’97) received the Dipl. Eng. Degree from the Université des Sciences et Technologies d’Oran, Algeria, in 1980. He Joined the Centre HyperfréquencesetSemiconducteurs, University of Lille 1,Villeneuve d’Ascq, France, in 1980. He received the Docteur-Ingénieur degree in 1984 from the University of Lille 1. In 1988, hejoined the Institut d’Electronique et de Microélectronique du Nord and received the Habilitation à Diriger les Recherches en Sciences Physiquesdegree, in 1996. Currently, he is Assistant

Professor at the University of Poitiers (IUT Angoulême, France) and associate member of XLIM Laboratory (Limoges, France). Research work concerns microwaves devices and circuits, FET nonlinear modeling, microwaves mixers, power amplifiers, non-linear CAD, millimeter wave MMIC’s and non-linear noise analysis.

Jean-Marie PAILLOT (M’95) received a PhD degree in Electronics form the University of Limoges, France, in 1990. His thesis was on the design of non-linear analog circuits and the study of the noise spectra of integrated oscillators. After graduation, he joined the Electronics Laboratory of PHILIPS Microwave, as R&D engineer in charge of the design of microwave monolithic integrated circuits. Since October 1992, J.M. Paillot is with the University of Poitiers, where he currently is Full Professor of Electronics Engineering and member of the Xlim Laboratory (Limoges-France). J.M. Paillot is presently

interested in phase noise reduction techniques for microwave oscillaltors, as well as in the research and development of circuits to command the antenna arrays.

an empirical large signal model for rf ldmosfet transistors

Technology

accurate large signal

measured output power

rf ldmosfet transistors

ldmosfet measurements

rf transconductance

output power of rf pa

source voltage vgs

power amplifier performance