LDMOS technology allows manufacturing high efficiency high gain amplif

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LDMOS technology allows manufacturing high efficiency high gain amplif

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Evaluation board using SD57045 LDMOS transistor broadcast application
LDMOS technology allows manufacturing high efficiency high gain amplifiers transmitters. LDMOS proven advantages against bipolar devices terms higher gain, efficiency, linearity, biasing simpleness that lower overall system cost make them attractive high volume businesses demanding cost power transistor solutions. Thanks 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 under supply. unmatched from making eligible variety applications, especially high performance, cost driver applications. This application note documents feasibility cost cellular device commercial driver. advantages LDMOS technology 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.
October 2007
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Contents
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Contents
Circuit design
Description consideration
Characterization results Conclusion Revision history
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List figures
List figures
Figure Figure Figure Figure Figure Figure Figure Figure Broadband transformer Broadband power amplifier Layout broadband power amplifier Drain current gate-source voltage Gate-source voltage case temperature Output power efficiency input power Power gain efficiency output power Class safe operating area
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Circuit design
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Circuit design
Description consideration
Input output impedances SD57045 shown Table below: Table Input output impedances
Frequency (MHz) input 10.8-j7.60 10.6-j8.36 10.5-j9.87 output 7.5-j0.15 7.8-j0.34 8.1-j0.61
With respect these impedances, transmission line auto transformers were designed using 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 from impedance port transformers (12.5 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 Broadband 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 resonant frequency above frequency
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Circuit design interest. Depending application, additional frequency bypass capacitors isolated with lossy elements (ferrite beads) required prevent power supply noise affecting gate drain circuits. Circuit schematic given Figure layout Figure with component values Table Table Bill material
Reference C1,C13 Board Description transmission line 1000 chip capacitor 39000 chip capacitor chip capacitor resistor 10000 chip capacitor resistor electrolytic capacitor resistor 1200 chip capacitor chip capacitor 25-115 variable cap-arco trimmer transformers, 10.7", 30mils, ounces copper, 2.55
Figure
Broadband power amplifier
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Characterization results Figure Layout broadband power amplifier
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Characterization results
Tcase Absolute maximum ratings
Parameter Drain-source voltage Drain-gate voltage (RGS Gate-source voltage Drain current Power dissipation TC=70°C) Operating junction temperature Storage temperature Value +/-20 Unit
Table
Symbol V(BR)DSS VDGR PDISS TJMax TSTG
Table
Symbol Rth(j-c)
Thermal data
Parameter Junction-case thermal resistance Value Unit °C/W
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AN1224 Figure Drain current gate-source voltage
Characterization results
DRAIN CURRENT
VGS, GATE-SOURCE VOLTAGE (VOLTS)
Figure
Gate-source voltage case temperature
VGS, GATE-SOURCE VOLTAGE (NORMALIZED)
1.04
1.02
Id=3A
Id=2A Id=1.5A Id=1A
0.98
0.96 Tcase, CASE TEMPERATURE (°C)
Id=250mA
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Characterization results Figure Output power efficiency input power
Pout
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Output Power
Freq=95 Idq=250 Vdd=28V
Input Power
Figure
Power gain efficiency output power
Gain
Freq=95 Idq=250 Vdd=28V
Pout
Figure
Class safe operating area
DRAIN CURRENT
Tc=70°C Tc=100°C
Tj=200°C
VDS, DRAIN-SOURCE VOLTAGE (VOLTS)
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Efficiency(%)
Gain (dB)
Efficiency
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Conclusion
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/rf.
Revision history
Table
Date 13-Sep-2007 26-Oct-2007
Document revision history
Revision content change Document reformatted content change Modified: title Changes
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LDMOS technology allows manufacturing high efficiency high gain amplif

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