MRF175LU Datasheet, PDF (7/7 Pages) Motorola, Inc – N-CHANNEL BROADBAND RF POWER FETs

MRF175LU
The RF MOSFET Line
100W, 400MHz, 28V
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 MRF175L 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-
M/A-COM Products
Released - Rev. 07.07
ance. The value of quiescent drain current (IDQ) is not critical
for many applications. The MRF175L was characterized at
IDQ = 100 mA, each side, which is the suggested minimum-
value of IDQ. For special applications such as linear amplifi-
cation, IDQ may have to be selected to optimize the critical
parameters. The gate is a dc open circuit and draws no cur-
rent. Therefore, the gate bias circuit may be just a simple
resistive divider network. Some applications may require a
more elaborate bias system.
GAIN CONTROL
Power output of the MRF175L 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.
7
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