ATF54143
Determine maximum permissible RF power input by means of
simulation
PC5M, C. Mobach
Zuiderkreek 4
3832KJ Leusden
The Netherlands
Contact: pc5m@pc5m.com
Oktober 11th 2010
ATF54143 Maximum permissible
RF input power
Leusden, The Netherlands,Oct 11th, 2010
A pc5m design
1 Introduction
During (contest) operation we used for the 70cm band some pre-amplifiers based on
the design of oz1pif (OZ1PIF, 2009). As an active element this design uses a Agilent ATF54143 Low Noise Enhancement Mode Pseudomorphic HEMT (Agilent, 2001). Preamplifiers were mounted near the antenna and switched by means of some RF
coaxrelais. Although performance is very good a number of HEMT’s where destroyed
during transceive operation. After ruling out any mall configuration in receive-transmit
sequencing the only cause of destruction could be the RF power at the input due to the
finite isolation of the coaxrelais. This paper investigates the permissible RF power level
at the input of the pre-amplifier and as such provides some metrics to the required
isolation level.
Investigation is done by simulation using Aplac a Circuit Simulation and design Tool
(Aplac, 2005).
2 Simulation
2.1 Simulation setup
The original oz1pif design was captured into the circuit simulator, slightly simplified by
omitting all DC related components. For the active element a linear 2-port model was used
(ATF54143, .s2p, 3V, 60mA). Extracted are the source, drain and gate (peak) voltages as well
as the gate current when the amplifier is excited with 100 uW. Frequency swept between
200 and 500 Mhz.
See appendix A, for the simulation input file.
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© 2010 , PC5M
ATF54143 Maximum permissible
RF input power
Leusden, The Netherlands,Oct 11th, 2010
A pc5m design
2.2 Simulation results
In the figure below the peak gate current is given as well as the maximum allowed gate
current for the HEMT according the manufactures specification. As can be seen the device is
at its limit with an input excitation of 100 uW.
PEAK GATE CURRENT
APLAC 8.10 Student version FOR NON-COMMERCIAL USE ONLY
2.5
Ig/mA
2
1.5
1
0.5
0
300M
350M
Igs peak
400M
f/Hz
450M
500M
Igs max
Figure 1: Peak gate current
Another interesting parameter are the peak gate-source and gate-drain voltages. In the
figure below those are given together with the permissible levels. As can bee seen, with an
excitation of 100uW those maximum levels are not reached.
PEAK GATE/SOURCE AND GATE/DRAIN VOLTAGES
APLAC 8.10 Student version FOR NON-COMMERCIAL USE ONLY
5
Vgd/V
4
3
2
1
0
300M
350M
Vgate-source
Vgd MAX
400M
450M
f/Hz
Vgate-drain
Vgs MAX
500M
Figure 2: Peak gate-source and gate-drain voltages
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© 2010 , PC5M
ATF54143 Maximum permissible
RF input power
Leusden, The Netherlands,Oct 11th, 2010
A pc5m design
To conclude also the gain of the total amplifier is simulated. Simulation result is very
close the actual measurement at the bench.
GAIN
APLAC 8.10 Student version FOR NON-COMMERCIAL USE ONLY
20
dB
15
10
5
0
300M
350M
GAIN
400M
f/Hz
450M
500M
Fig 3. Power gain
3 Conclusion
For this design, RF power levels at the input in access of 100uW (-10dBm) will lead to HEMT
destruction and therefore should be prohibited at all means. To put this permissible level
into perspective, the TX coaxrelais should have an isolation over 70 dB when applying TX
power levels of 1000W (+60dBm). A measurement on regularly used types such as CX520
reveals that those are marginally adequate and should not be used or in conjunction with a
second (small, but low loss) coaxrelais to improve isolation.
Further improvements on the simulation results could be done by using not the small signal
model of the HEMT but incorporating the large signal model in conjunction with e.g.
harmonic balance circuit simulation.
4 Bibliografie
Agilent. (2001). http://www.avagotech.com/docs/AV02-0488EN. Retrieved from avagotech:
http://www.avagotech.com/docs/AV02-0488EN
Aplac. (2005). Retrieved from www.aplac.com: http://www.aplac.com
ATF54143, .s2p, 3V, 60mA. (n.d.). Retrieved from http://www.avagotech.com/docs/MPUB811
OZ1PIF. (2009). 144 & 432 MHz High IIP3 PA3BIY LNAs. Retrieved from
http://frenning.dk/OZ1PIF_HOMEPAGE/144_and_432MHz-LNA.htm
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© 2010 , PC5M
ATF54143 Maximum permissible
RF input power
5
Leusden, The Netherlands,Oct 11th, 2010
A pc5m design
© 2010 , PC5M
ATF54143 Maximum permissible
RF input power
Leusden, The Netherlands,Oct 11th, 2010
A pc5m design
5 Appendix A, simulation file
NPort NPort1 2 GATE SOURCE DRAIN SOURCE
+ load = "af541433b.s2p"
Cap C1 IN node1
+ 3.3p
Ind L2 node1 GATE2
+ 4n
Ind L3 SOURCE GND
+ 1n
Cap C2 node1 GND
+ 6p
Ind L1 node1 GND
+ 12n
Res R7 node2 GND
+ 60
Res R8 node2 OUT
+ 12
Res R9 OUT GND
+ 50
Volt V1 IN GND
+ R = 50
+ AC = Udbr(0,50,100u)
Res R10 DRAIN node2
+ 10
Res R12 GATE2 GATE
+1
Res R11 SOURCE GND
+ 75
$ MEASUREMENTS:
$ ------------Sweep "ATF MAX POWER"
+ LOOP 301 FREQ LIN 300Meg 500Meg
+ w 2 Y "dB" "" 0 20 TITLE="GAIN"
+ w 3 Y "Vgd" "V" 0 5 TITLE="PEAK GATE/SOURCE AND GATE/DRAIN VOLTAGES" NYTICKS=6
+ w 4 Y "Ig" "mA" 0 2.5 TITLE="PEAK GATE CURRENT"
show
+ w 2 Y dB(Mag(Vac(OUT)/Vac(IN))) NAME="GAIN"
+ w 3 Y Mag(Vac(GATE)-Vac(SOURCE)) NAME="Vgate-source" MARKER=1
+ w 3 Y Mag(Vac(GATE)-Vac(DRAIN)) NAME="Vgate-drain" MARKER=2
+ w 3 Y 5 NAME = "Vgd MAX" COLOR="Red" MARKER=2
+ w 3 Y 1 NAME = "Vgs MAX" COLOR="Red" MARKER=1
+ w 4 Y Mag(Vac(GATE)-Vac(GATE2))*1000 NAME="Igs peak"
+ w 4 Y 2 NAME ="Igs max" COLOR = "Red"
EndSweep
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© 2010 , PC5M