mga-444940-02 MicroWave Technology, Inc., mga-444940-02 Datasheet - Page 3

• Manufacturer Part Number: mga-444940-02
• Description: 4.4 - 4.9 Ghz 10w High Efficiency High Power Amplifier
• Manufacturer: MicroWave Technology, Inc.

APPLICATION NOTE
Rogers 4003 material, 20 mil thick, and 2 oz copper
weight and is used to evaluate the MGA444924-02
hardware. The 10 watt device in the ‘02’ package has a
limited temperature range of approximately 85°C. An
earless flange or flange package is offered with better Tjc
and can be used at much higher temperatures. Please
consult the factory for your specific application. Through
holes with a diameter of 20 mils are placed uniformly over
the center pad for thermal relief and RF ground.
It is recommended that via holes be placed near the DC bias connector to maintain ground continuity between the top layer
and bottom ground planes. Mounting holes near the unit will help secure the board to the chassis, minimize ground current
loops and improve thermal conductivity in the absence of sweat soldering the board to the chassis. Biasing with quarter-
wave stubs at the gate and drain are shown in Figure 1. The impedance of the quarter wave structures is cyclical with
frequency. A RF short is observed at frequencies that are even multiples of quarter-wavelength and open impedance is
observed at frequencies that are odd multiples of a quarter-wavelength. A 56 ohm resistor is added in series to the gate
bias. The effective impedance is increased which reduces the risk of oscillations. The 56 ohm resistor is not shown in
Figure 1. Through holes underneath the package is required to connect the top and bottom grounds and to improve
thermal conductivity. The through holes can be back filled with conductive epoxy for best thermal performance. The
MGA444940-02 has a noise figure less than 3.0 dB. A plot of noise figure versus frequency at Idq is shown in Figure 2. At
small signal levels the amplifier operates at Idq. As the output power is increased the amplifier drive current will increase. A
plot of Pout versus Pin shown in Figure 3 is plotted from 25 dBm to 40 dBm. The drain current Idd increases from 0.10 to
0.89 A. The RF drive level is increased incrementally and stopped when the gate leakage current of 10 mA is reached. The
temperature performance for Pout vs Pin has a slope of -0.019 dB/!. A plot of Pout vs Pin at 4.7 GHz over a temperature
range from 0 to 85! is shown in Figure 4.
The Burst power and ACPR data are shown in Figure 5. These measurements are recorded at EVM=2.5% across the
frequency range at 4.4, 4.7, 4.9 and 5.1 GHz. A WPS44492202 amplifier is used as the drive stage and has a residual
EVM error of less than 0.8%. The modulation is 802.16x and each frame cycle has a 10 msec duration and runs
continuously. Equalization is enabled when measuring EVM performance. The MGA amplifier bias condition is Vdd=28V
and the gate voltage is adjusted for an Idq=100 mA. A diagram of test setup is shown in Figure 7 and includes the frame
information about the test pattern. As the output power is backed off from the peak performance, the amplifier changes its
DC/RF operation from Class ‘A’ to Class ‘A/B’. An example of this dynamic DC/RF operation can be obverse in EVM
versus Burst Power performance shown in Figure 6. The EVM is optimal at 33 dBm but not at 25 dBm in which the output
power is backed off and the amplifier’s operating current to reduced 150 mA. At this bias condition the amplifier is back-off
near pinch off.
Applications that require gating the amplifier for TDD applications can be supported using a constant current source with a
command switch to disable current loop and turnoff the amplifier as shown in Figure 9. A 1% precision resistor R8 0.2 ohm
is used to convert the current to voltage. Applying KVL principal around Q2 and Q3, the current through Q2 and the load
current is 30 times defined by resistor network R4 over R8. As the load current is equalized, the gate voltage to the gate of
the GaN is adjusted until the voltage at Q3 base and voltage at Q2 collector is balanced. A MOSFET M2 is used to enable
and disable the loop. The loop bandwidth has been intentionally truncated to minimize the loop dynamics from attacking
the envelope. This allows the bias current to increase as the Pout increases; this is shown in Figure 8.
Fremont, CA 94538
4268 Solar Way
[e-mail]
The evaluation board material, shown in Figure 1, is
FIGURE 1 Evaluation Board
4.4 - 4.9 GHz 10W High Efficiency
Data Sheet and Application Note
MGA-444940-02
High Power Amplifier
www.mwtinc.com
P [phone]
F [phone]
May 2010