An empirical large signal model for rf ldmosfet transistors

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

COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)

ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Special Issue (November, 2013), pp. 01-07
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An Empirical Large Signal Model for RF LDMOSFET Transistors
M Tamoum1, R Allam2, J M Paillot2
2CNRS-XLIM,
1

1Université de Jijel, Jijel, Algeria
UMR 7252, Université de Poitiers, Angoulême (France)

tamo_moha@yahoo.fr, 2rachid.allam@univ-poitiers.fr, 3jean.marie.paillot@univ-poitiers.fr

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

October 18-20, 2013
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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:
VGS

I DS 

G

m

(VGS ,VDS 0 ) dVGS  Gd (VGS ,VDS 0 )(VDS  VDS 0 )

(1)

VTH

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:
n

Gm (VGS ,VDSo )   a p . GS .F (VGS )
VP

(2)

p 0

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


October 18-20, 2013
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VGS

QGS 

C

GS

(VGS ,VDSo )dVGS  K .VGS

(3)

VTH

With:
n
P
CGS (VGS ,VDSo )   bp .VGS .F (VGS )

(4)

p 0

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.

Transconductance, Gm (mS)

700

Measure
Interpolation

600
500
400
300
200
100
0
0

1

2

3

4

5

6

7

8

Gate-Source Voltage, Vgs (V)

Fig. 2: Comparison between measured and interpolated transconductance

Drain Conductance, Gd (mS)

7

Measure
Interpolation

6
5
4
3
2
1
0
0

1

2

3

4

5

6

7

8


Fig. 3: Comparison between measured and interpolated conductance

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Gate-Source Capacitance, Cgs (pF)

25

Measure
Interpolation

20
15
10
5
0
0

2

4

6

8


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

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Output Power, Pout (dBm)

40

Measure
Simulation
30

20

10

0
0

5

10

15

20

25

30

Input Power, Pin (dBm)

Fig. 6: Comparison between measured and simulated output power
20

Measure
Simulation

Power Gain, Gp (dB)

16
12
8
4
0
0

5

10

15

20

25

30


Fig. 7: Comparison between measured and simulated power gain
100

Measure
Simulation

Efficiency (%)

80
60
40
20
0
0

5

10

15

20

25

30


Fig. 8: Comparison between measured and simulated efficiency

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Drain-Source Current, Ids (mA)

1600

Measure
Simulation
1200

800

400

0
0

5

10

15

20

25

30


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 selfheating 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.

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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 cooperated 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 nonlinear 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.


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An empirical large signal model for rf ldmosfet transistors

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