AN1941 Freescale Semiconductor / Motorola, AN1941 Datasheet

AN1941

Manufacturer Part Number

AN1941

Description

Modeling Thermal Effects in RF LDMOS Transistors

Manufacturer

Freescale Semiconductor / Motorola

Datasheet

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MOTOROLA

SEMICONDUCTOR APPLICATION NOTE

Modeling Thermal Effects in RF LDMOS Transistors

Prepared by: Darin Wagner

INTRODUCTION

important consideration when simulating in an elevated

temperature environment. An improperly modeled biasing

network can show a required gate voltage (V

current probe (I

example, this application note illustrates the different results

obtained from a simulation using two models: Motorola’s

MRF19125 Root model and MET (Motorola Electro Thermal)

model. All examples contained within this application note are

based on simulation results from Agilent EEsof EDA

Advanced Design System (ADS).

ROOT MODEL

the HP Root FET Model generator. The model generator

creates

small–signal S–parameter and measured DC data. The Root

model predicts device performance as a function of bias,

NOTE: For better viewing on the Web, click on link for larger version of graphic.

REV 0



MOTOROLA SEMICONDUCTOR APPLICATION INFORMATION

The temperature effects in high power amplifiers are an

The Root model is a data–based model that is created from

Motorola, Inc. 2002

device–specific,

Motorola Semiconductor Products Sector

) that may be completely inaccurate. As an

Figure 1. Basic Block Diagram of Generic Components Used to Set Up Simulation

large–signal

Freescale Semiconductor, Inc.

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) for a desired

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model

from

frequency and power level. This model enables circuits to be

simulated that contain devices for which measured data exists

but good physical or empirical models do not.

MET MODEL

account for the dynamic self–heating effects inherent in high

power RF LDMOS transistors. The LDMOS MET model is an

empirical large–signal, nonlinear model. The MET model can

accurately represent the current–voltage characteristics and

their derivatives at any bias point and temperature.

Figure 1 shows the generic

simulations. The first simulation compares the Root and MET

models and shows the potential errors associated with the

Root model vs. the MET model at higher quiescent currents.

The second simulation is a sweep of heatsink temperature

and shows the effect of temperature on the current probe (I

at various gate voltages (V

The MET model is an electro thermal model that can

Two simulations are illustrated in this application note.

) at a constant drain voltage

components used for the

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AN1941 Summary of contents

Page 1

... Root model vs. the MET model at higher quiescent currents. The second simulation is a sweep of heatsink temperature model from and shows the effect of temperature on the current probe (I at various gate voltages ( to: www.freescale.com Order this document by AN1941/D AN1941 components used for the ) constant drain voltage GS 1 ...

Page 2

... Freescale Semiconductor, Inc. AN1941 ROOT MODEL VS. MET MODEL SIMULATION SETUP In the Root vs. MET model simulation, a family of curves is generated using a basic DC simulation (DC1) and a parameter sweep (Sweep1) (Figure 2). The simulator outputs IV curves for the Root and the MET models superimposed on each other. ...

Page 3

... The DUT is terminated with 50 Ω termination ports. • DC blocking caps with values appropriate for the band of operation are used. • Parameter Sweep is set up with V global sweep variable. • DC1 calls on a separate DC simulation named and T FLANGE Sweep1, which then sweeps T Go to: www.freescale.com AN1941 defined as the GS . SNK 3 ...

Page 4

... Freescale Semiconductor, Inc. AN1941 NOTE: For better viewing on the Web, click on link for larger version of graphic. Figure 4. MET Model T (heat sink) RESULTS The results shown in Figure 4 illustrate the importance of careful selection of a fixture’s operating temperature and V At lower quiescent currents (200 mA to 1000 mA), the drain– ...

Page 5

... RF simulations in ADS. These topics are beyond the scope of this application note and will be discussed in subsequent ADS user application notes. To access all Motorola RF LDMOS Model libraries, go to: http://www.motorola.com/rf/models Go to: www.freescale.com AN1941 , is predefined by ADS ...