MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Designed primarily for wideband large–signal output and
driver stages from 100 – 500 MHz.
Rev. V1
Product Image
N-Channel enhancement mode
Guaranteed performance @ 500 MHz, 28 Vdc
Output power — 150 W
Power gain — 10 dB (min.)
Efficiency — 50% (min.)
100% tested for load mismatch at all phase angles
with VSWR 30:1
Overall lower capacitance @ 28 V
Ciss — 135 pF
Coss — 140 pF
Crss — 17 pF
Simplified AVC, ALC and modulation
CASE 375–04, STYLE 2
Typical data for power amplifiers in industrial and
commercial applications:
Typical performance @ 400 MHz, 28 Vdc
Output power — 150 W
Power gain — 12.5 dB
Efficiency — 60%
Typical performance @ 225 MHz, 28 Vdc
Output power — 200 W
Power gain — 15 dB
Efficiency — 65%
1
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
2
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
3
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
4
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
5
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
6
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
7
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
8
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
10
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
11
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
12
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
13
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
14
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
15
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
16
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
RF POWER MOSFET CONSIDERATIONS
MOSFET CAPACITANCES
The physical structure of a MOSFET results in capacitors between the terminals. The metal oxide gate structure determines the capacitors from gate–to–drain (Cgd),
and gate–to–source (Cgs). The PN junction formed during the fabrication of the MOSFET results in a junction
capacitance from drain–to–source (Cds).
These capacitances are characterized as input (Ciss),
output (Coss) and reverse transfer (Crss) capacitances
on datasheets. The relationships between the inter–
terminal capacitances and those given on data sheets
are shown below. The Ciss can be specified in two ways:
1.
2.
Drain shorted to source and positive voltage at
the gate.
Positive voltage of the drain in respect to source
and zero volts at the gate. In the latter case the
numbers are lower. However, neither method
represents the actual operating conditions in RF
applications.
The Ciss given in the electrical characteristics table
was measured using method 2 above. It should be noted
that Ciss, Coss, Crss are measured at zero drain current
and are provided for general information about the device. They are not RF design parameters and no attempt
should be made to use them as such.
DRAIN CHARACTERISTICS
One figure of merit for a FET is its static resistance in
the full–on condition. This on–resistance, VDS(on), occurs in the linear region of the output characteristic and is
specified under specific test conditions for gate–source
voltage and drain current. For MOSFETs, VDS(on) has a
positive temperature coefficient and constitutes an important design consideration at high temperatures, because
it contributes to the power dissipation within the device.
GATE CHARACTERISTICS
The gate of the MOSFET is a polysilicon material, and
is electrically isolated from the source by a layer of oxide.
The input resistance is very high — on the order of 109
ohms — resulting in a leakage current of a few nanoamperes. Gate control is achieved by applying a positive
voltage slightly in excess of the gate–to–source threshold
voltage, VGS(th).
Gate Voltage Rating — Never exceed the gate voltage rating (or any of the maximum ratings on the front
page). Exceeding the rated VGS can result in permanent
damage to the oxide layer in the gate region.
17
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Gate Termination — The gates of this device are essentially capacitors. Circuits that leave the gate open–circuited
or floating should be avoided. These conditions can result in
turn–on of the devices due to voltage build–up on the input
capacitor due to leakage currents or pickup.
Gate Protection — These devices do not have an internalmonolithic zener diode from gate–to–source. If gate protection is required, an external zener diode is recommended.
Using a resistor to keep the gate–to–source impedance low
also helps damp transients and serves another important
function. Voltage transients on the drain can be coupled to
the gate through the parasitic gate–drain capacitance. If the
gate–to–source impedance and the rate of voltage change
on the drain are both high, then the signal coupled to the
gate may be large enough to exceed the gate–threshold
voltage and turn the device on.
HANDLING CONSIDERATIONS
When shipping, the devices should be transported only in
antistatic bags or conductive foam. Upon removal from the
packaging, careful handling procedures should be adhered
to. Those handling the devices should wear grounding
straps and devices not in the antistatic packaging should be
kept in metal tote bins. MOSFETs should be handled by the
case and not by the leads, and when testing the device, all
leads should make good electrical contact before voltage is
applied. As a final note, when placing the FET into the system it is designed for, soldering should be done with
grounded equipment.
DESIGN CONSIDERATIONS
The MRF275G is a RF power N–channel enhancement
Rev. V1
mode field–effect transistor (FETs) designed for HF, VHF
and UHF power amplifier applications. M/A-COM RF MOSFETs feature a vertical structure with a planar design. M/ACOM Application Note AN211A, FETs in Theory and Practice, is suggested reading for those not familiar with the construction 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 mismatched loads without suffering damage. Power output can be varied over a wide
range with a low power dc control signal.
DC BIAS
The MRF275G is an enhancement mode FET and, therefore, 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 performance. The value of quiescent drain current (IDQ) is not critical for many applications. The MRF275G was characterized
at IDQ = 100 mA, each side, which is the suggested minimum value 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 system.
GAIN CONTROL
Power output of the MRF275G 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.
18
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
19
M/A-COM Technology Solutions Inc. (MACOM) and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice.
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MRF275G
The RF MOSFET Line
150W, 500MHz, 28V
Rev. V1
M/A-COM Technology Solutions Inc. All rights reserved.
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M/A-COM Technology Solutions Inc. (MACOM) and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice.
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