Ahmed Mimouni ABSTRACT LDMOS technology allows manufacturing high

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Ahmed Mimouni ABSTRACT LDMOS technology allows manufacturing high

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LDMOS POWER TRANSISTORS BROADBOARD APPLICATION
Ahmed Mimouni
ABSTRACT LDMOS technology allows manufacturing high efficiency high gain amplifiers transmitters. LDMOS proven advantages against bipolar devices terms higher gain, efficiency, linearity, biasing simpleness that lowers overall system cost makes them attractive high volume businesses demanding cost power transistor solutions. these advantages, LDMOS power transistors proven mainstay power amplifier business cellular base station today. device used present characterization, SD57045, STMicroelectronics product, lateral current, double diffused transistor that delivers watts Volts. unmatched from making eligible variety applications, especially high performance, cost driver applications. This application note documents feasibility cost cellular device commercial driver. advantages LDMOS technologies improved thermal resistance reduced source output inductance. wire-bonded connections external circuitry (DMOS config.) longer required because source chip surface connected substrate diffusion highly doped p-type region. Consequently, LDMOS excellent high frequency response because high superior gain feedback capacitance reduced source inductance. additional advantage LDMOS structure that Beryllium oxide (BeO), toxic electrical insulator required isolate drain with DMOS transistors, longer needed. Hence, only thermal resistance improved, package cost environmental impact significantly reduced. Finally, LDMOS, parasitic bipolar been nullified guaranteeing good ruggedness, efficiency high current handling capability. CIRCUIT DESIGN: DESCRIPTION CONSIDERATION. Input output impedances SD57045 shown table below: Table
Frequency (MHz) 10.8-j7.60 10.6-j8.36 10.5-j9.87 input 7.5-j0.15 7.8-j0.34 8.1-j0.61 output
With respect these impedances, transmission line auto transformers were designed using Ohm, wavelength, semi rigid coaxial cable. achieve this transformation across band, capacitor added impedance port each transformer cancel leakage inductance. frequency response shown figure Simple L-sections were utilized make final transformation
July 2000
AN1224 APPLICATION NOTE from impedance port transformers (12.5 Ohms) measured impedances device (see table This design uses printed series inductors Glass Teflon board. gain power extremely high from throughout frequency band. feedback network necessary suppress frequency gain, well give nominal amount gain frequency interest. This feedback also helps increase input impedance. Since LDMOS such high gain frequencies, value, high power, flange mount resistor must comprised design. capacitor feedback path (C3) provides negative feedback frequencies. This component designed self-resonant. below band, MHz, capacitor looks slightly inductive, reducing amount feedback band interest. Figure Broad Band Transformer
-30dB
-60dB
80MHz
90MHz
100MHz
110MHz
Unbalanced transformers offer efficient matching method from impedance. Besides, auto transformers have zero impedance point over broad bandwidth, offering ideal feeding point gate drain circuits. order prevent high frequency oscillations, bypass capacitor used zero impedance point transformer. Capacitor value must selected that self resonant frequency above frequency interest. Depending application, additional frequency bypass capacitors isolated with lossy elements (ferrite beads) required prevent power supply noise affecting gate drain circuits.
AN1224 APPLICATION NOTE Circuit schematic given figure layout figure with component values table Table L1,L3, C1,C13 C4,C6, C5,C12 L2,L6 Board transmission line 1000 chip capacitor 39000pF chip capacitor 36pF chip capacitor resistor 10000pF chip capacitor resistor 10uF, electrolytic capacitor resistor 1200pF chip capacitor 33pF chip capacitor 25-115pF variable cap-Arco trimmer transformers, 10.7", 30mils, ounces copper, 2.55
Figure Broad Band Power Amplifier
AN1224 APPLICATION NOTE Figure Layout Broad Band Power Amplifier
CHARACTERIZATION RESULTS. Absolute maximum ratings (TCASE Table Symbol V(BR)DSS VDGR PDISS TJMax TSTG Thermal data TH(j-c) Junction-Case Thermal Resistance Parameter Drain-Source Voltage Drain-Gate Voltage (RGS Gate-Source Voltage Drain Current Power Dissipation TC=70 Operating Junction Temperature Storage Temperature Value +/-20
Unit
AN1224 APPLICATION NOTE Figure Drain Current Gate-Source Voltage
Drain Current Gate-Source Voltage
DRAIN CURRENT VGS, GATE-SOURCE VOLTAGE (VOLTS)
Figure Gate-Source Voltage versus Case Temperature
Gate-Source Voltage Case Temperature
1.04
VGS, GATE-SOURCE VOLTAGE (NORMALIZED)
1.02
Id=3A
Id=2A Id=1.5A Id=1A
0.98
0.96 Tcase, CASE TEMPERATURE (°C)
Id=250mA
Figure Output Power Effeciency versus Input Power
Output Power Efficiency Input Power
Pout
Output Power
Freq=95 Idq=250 Vdd=28V
Input Power
Efficiency
AN1224 APPLICATION NOTE Figure Power Gain Efficiency Output Power
Power Gain Efficiency Output Power
Gain
Freq=95 Idq=250 Vdd=28V
Pout
Figure Class Safe Operating Area
Class Safe Operating Region
DRAIN CURRENT
Tc=70°C Tc=100°C
Tj=200°C
VDS, DRAIN-SOURCE VOLTAGE (VOLTS)
CONCLUSION this application note have demonstrated feasibility cost, cellular device commercial driver. conclude that LDMOS technology offers viable solutions power amplifiers frequencies covering high throughout high bands. More information about these devices found http://www.st.com.
Efficiency(%)
Gain (dB)
AN1224 APPLICATION NOTE
Information furnished believed accurate reliable. However, STMicroelectronics assumes responsibility consequences such information infringement patents other rights third parties which result from use. license granted implication otherwise under patent patent rights STMicroelectronics. Specification mentioned this publication subject change without notice. This publication supersedes replaces information previously supplied. STMicroelectronics products authorized critical components life support devices systems without express written approval STMicroelectronics. logo trademark STMicroelectronics 2000 STMicroelectronics Printed Italy rights reserved
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Ahmed Mimouni ABSTRACT LDMOS technology allows manufacturing high

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