MRF5015 Datasheet, PDF (7/8 Pages) Motorola, Inc – N-CHANNEL BROADBAND RF POWER FET

AMPLIFIER DESIGN
Impedance matching networks similar to those used with
bipolar transistors are suitable for the MRF5015. 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 MRF5015
yield a device quite capable of self oscillation. Stability may
be achieved by techniques such as drain loading, input shunt
resistive loading, or output to input feedback. Different
stabilizing techniques may be required depending on the
desired gain and bandwidth of the application. The RF test
fixture implements a parallel resistor and capacitor in series
with the gate to improve stability and input impedance Q.
Two port stability analysis with the MRF5015 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.
MOTOROLA RF DEVICE DATA
MRF5015
7