MRF5007 Datasheet, PDF (8/10 Pages) Motorola, Inc – N-CHANNEL BROADBAND RF POWER FET

MOUNTING
The specified maximum thermal resistance of 7.0°C/W as-
sumes a majority of the 0.137″ x 0.185″ source contact on
the back side of the package is in good contact with an ap-
propriate heat sink. In the test fixture shown in Figure 1, the
device is clamped directly to a copper pedestal. As with all
RF power devices, the goal of the thermal design should be
to minimize the temperature at the back side of the package.
It is recomended that this temperature not exceed 100°C for
any operating condition. Contact customer service for addi-
tional information on thermal considerations for mounting.
AMPLIFIER DESIGN
Impedance matching networks similar to those used with
bipolar transistors are suitable for the MRF5007. For exam-
ples see Motorola Application Note AN721, “Impedance
Matching Networks Applied to RF Power Transistors.” Both
small–signal S–parameters and large–signal impedances
are provided. While the S–parameters will not produce an
exact design solution for high power operation, they do yield
a good first approximation. This is an additional advantage of
RF power MOSFETs.
Since RF power MOSFETs are triode devices, they are not
unilateral. This coupled with the very high gain of the
MRF5007 yields a device capable of self oscillation. Stability
may be achieved by techniques such as drain loading, input
shunt resistive loading, or output to input feedback. The RF
test fixture implements a parallel resistor and capacitor in se-
ries with the gate and has a load line selected for a higher
efficiency, lower gain, and more stable operating region.
Two port stability analysis with the MRF5007 S–parame-
ters provides a useful tool for selection of loading or feed-
back circuitry to assure stable operation. See Motorola
Application Note AN215A, “RF Small–Signal Design Using
Two–Port Parameters,” for a discussion of two port network
theory and stability.
MRF5007 MRF5007R1
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MOTOROLA RF DEVICE DATA