Application Note 1128 Hewlett-Packard ATF-36077 PHEMT device desc

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Application Note 1128 Hewlett-Packard ATF-36077 PHEMT device desc

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Band Amplifier using ATF-36077 Noise PHEMT
Application Note 1128
Hewlett-Packard ATF-36077 PHEMT device described noise amplifier that easily optimized spot frequency through 1800 frequency range. ATF-36077 intended used noise amplifier applications providing noise figures. device capable noise figures below frequencies below GHz. Although device inherent noise figure around actual circuit losses limit minimum noise figure that obtained about
pedance device over wide frequency range. case ATF-36077, resistor small amount series inductance used provide shunt loading device. series inductance also provides some impedance matching. additional series resistor directly drain also used enhance stability. This circuit topology produces acceptable gain while ensuring good output match retaining stability over wide bandwidth possible. Obtaining lowest possible noise figure from device requires that input matching network convert nominal
source impedance opt. case ATF-36077 GHz, series inductor provides good noise match. source leads ATF-36077 must grounded with minimal source inductance. customary bypassed source resistor technique biasing typical MESFET such ATF-10136 will work very well with PHEMT device. Excessive source inductance will cause device oscillate frequencies around GHz. ATF-36077 will perform very well plated through holes placed directly under source leads adjacent package printed cir-
Design
Achieving associated gain which device capable difficult since device inherently stable desired operating frequency. enough that amplifier stable operating frequency must stable frequencies. out-of-band oscillation will make amplifier unusable. simplest technique ensure broad-band stability resistively load drain. Resistive loading produces constant
Table ATF-36077 Performance
Frequency (MHz) 1100 1150 1200 1250 1300 1350 1400 1450 1500 1550 1600 Gain (dB) 19.5 20.8 22.4 22.6 21.2 20.5 19.5 18.6 17.5 Noise Figure (dB) 0.53 0.60 0.44 0.38 0.33 0.31 0.28 0.28 0.30 0.30 0.40
cuit board thickness kept 0.031 inch less. schematic diagram parts list shown Figure schematic diagram suggests active biasing preset bias point. device biased nominal Volts operation will explained next section.
Passive biasing used will require that potentiometer connected output converter gate voltage bias required nominal drain current.
Performance
performance amplifier shown Table Since loss input microstripline
OUTPUT
INPUT
LL1/2
appreciable loss which adds directly noise figure, breadboard amplifier built without significant microstrip etch input network. optimum noise figure about this occurs over about bandwidth, centered 1400 MHz. noise figure rises 1600 0.44 1200 making amplifier usable broadband applications. amplifier tuned other frequencies through 1800 frequency range either increasing decreasing value inductor
Biasing
CHIP CAPACITOR CHIP CAPACITOR USED 1000 CHIP CAPACITOR USED, GROUND SOURCES DIRECTLY USED C12, CHIP CAPACITOR C10, CHIP CAPACITOR 0.007" DIA. WIRE, 0.050" 0.14" LENGTH 0.18 0.33 LL1, PLATED THROUGH HOLES BACKSIDE GROUNDPLANE DIRECTLY UNDER EACH LEAD HEWLETT-PACKARD ATF-36077 PHEMT CHIP RESISTOR USED CHIP RESISTOR USED CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR (SETS DRAIN VOLTAGE) CHIP RESISTOR (SETS DRAIN CURRENT) CHIP RESISTOR OHMS LINEAR TECHNOLOGY LTC1044CS8 VOLTAGE CONVERTER VOLT REGULATOR TOKO TK11650U OPTIONAL MMIC USED MICROSTRIPLINE, MINIMIZE LENGTH INPUT MINIMIZE LOSS EFFECT NOISE FIGURE
preferred method biasing FETs active bias network described Figure Although active biasing does cost requiring extra components, including generating negative voltage, advantages generally outweigh disadvantages. Active biasing offers advantage that variations pinchoff voltage Idss will necessitate change either source drain resistor value given bias condition. active bias network automatically sets desired drain current. typical active biasing scheme FETs requires that source leads grounded additional supply used generate negative voltage required gate typical operation. Referring Figure resistors provide regulated voltage base voltage increased volts virtue emitter-base junction then applied drain Since series with drain, voltage drop
Figure Schematic Parts List ATF-36077
across must taken into account when designing bias circuitry. Resistor connected between regulated voltage points therefore sets drain current. gate connected voltage divider consisting connected between collector negative voltage converter. gate voltage then assume value necessary sustain desired drain current.
2.1"
UHFLNC GaAsFET DEMO BOARD .031 FR-4 AJW12/96 INPUT OUTPUT
GaAsFET Demo Board
typical printed circuit board built 0.031 inch FR-4/G-10 shown Figures This board described detail Application Note 1076. input microstripline significant loss which mask some device noise figure. measured loss input microstripline excluding blocking capacitor 1600 0.15 MHz. Keep this loss mind when evaluating devices most computer simulations appear optimistic about dielectric board losses therefore give optimistic (lower) prediction noise figure. order best evaluate noise performance ATF-36077 without excessive input etch losses, board shown Figures modified. input connector soldered bottom groundplane installed close possible input inductor This allowed removal most input etch. performance shown Table reflects changes demo board described above. earlier version artwork locations
Figure GaAsFET Demo Board showing component placement
2.1"
UHFLNC AJW12/96 INPUT
GaAsFET DEMO BOARD 0.031 FR-4 OUTPUT
Figure GaAsFET Demo Board Artwork
reversed. When nearest microstripline, capacitive effect mounting junction shunts ground. result increased noise figure. therefore better have inductor first then followed resistor since impedance choke higher than that resistor. very difficult obtain very noise, high gain unconditional stability with high performance HEMT Band frequencies. Therefore, resistor R10, shown Figure used series with drain reduce
gain improve stability. Increasing this resistor much beyond will have adverse effect noise figure, i.e. >0.2
Case Difficulty
Generally noise figure should within couple tenths that indicated performance table gain within noise figure gain expected then check bias conditions. between volts drain current about bias voltage current adjustable, does performance maximize rated bias conditions some other values?
then problem excessive source inductance which causing high frequency oscillation. device oscillating frequency, even band frequency, difficult obtain rated performance. Make sure plated through holes close device possible, i.e., 0.02 0.03 inch long. problem inband stability, then solution series resistance between drain output connector. Increase value R10. Additional gain reduction also decreasing length shunt output inductor series with some cases, higher than expected noise figure attributed noise from converter transistor used active biasing. bypass capacitor parallel with location should help. lossy choke contribute increase noise figure. small molded choke works well prototypes. surface mount applications sure choose high wire wound choke such those made CoilCraft.
some instances, enclosure cause undesirable feedback across circuit board which cause instabilities. This phenomena true amplifier design. cross sectional view housing viewed piece waveguide whose dimensions, both width height, determine band frequencies that pass with minimal attenuation. combination amplifier response along with housing response could contribute instabilities controlled. profile surface mount components will minimize this effect. Making sure that cover closer printed circuit board than necessary will minimize coupling from cover. preferred have cover least inches above circuit board. ECOSORBcan used cover minimize reflections cover close proximity board. metal divider hanging down from cover also another method breaking enclosure effects.
cuit been shown that provides stable Band operation. single-element input matching network provides very good performance this frequency range offers greatest bandwidth least sensitivity manufacturing tolerances. resistive loading output network provides best broadband stable performance sacrificing some in-band gain.
Conclusion
ATF-36077 provide less than noise figures over several hundred bandwidth Band frequencies. simple cirFor technical assistance location your nearest Hewlett-Packard sales office, distributor representative call: Americas/Canada: 1-800-235-0312 (408) 654-8675 East/Australasia: Call your local sales office. Japan: 3335-8152 Europe: Call your local sales office. Data Subject Change Copyright 1997 Hewlett-Packard Printed U.S.A. 5966-0783E (11/97)

Application Note 1128 Hewlett-Packard ATF-36077 PHEMT device desc

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