MRF175GU_17 Datasheet, PDF (16/17 Pages) M/A-COM Technology Solutions, Inc. – The RF MOSFET Line 200/150W, 500MHz, 28V

MRF175GU
The RF MOSFET Line
200/150W, 500MHz, 28V
Rev. V1
COM Application Note AN211A, FETs in Theory and Prac-
tice, is suggested reading for those not familiar with the con-
struction and characteristics of FETs.
The major advantages of RF power FETs include high
gain, low noise, simple bias systems, relative immunity from
thermal runaway, and the ability to withstand severely mis-
matched loads without suffering damage. Power output can
be varied over a wide range with a low power dc control sig-
nal.
DC BIAS
The MRF175G is an enhancement mode FET and, there-
fore, does not conduct when drain voltage is applied. Drain
current flows when a positive voltage is applied to the gate.
RF power FETs require forward bias for optimum perform-
ance. The value of quiescent drain current (IDQ) is not critical
for many applications. The MRF175G was characterized
at IDQ = 100 mA, each side, which is the suggested mini-
mumvalue of IDQ. For special applications such as linear
amplification, IDQ may have to be selected to optimize the
critical parameters. The gate is a dc open circuit and draws
no current. Therefore, the gate bias circuit may be just a
simple resistive divider network. Some applications may
require a more elaborate bias sytem.
GAIN CONTROL
Power output of the MRF175G may be controlled from its
rated value down to zero (negative gain) by varying the dc
gate voltage. This feature facilitates the design of manual
gain control, AGC/ALC and modulation systems.
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