RFHA3942 Application Note
500MHz to 2500MHz, 48V Reference Design
Abstract
This application note is intended to provide a reference point for an amplifier circuit design using RFMD’s
RFHA3942 in a single-ended class AB amplifier configuration. The frequency of operation is optimized for
500MHz to 2500MHz. The operating drain voltage is 48VDC. At an output power of +43dBm, the gain >10dB
and >25%.
The RFHA3942 is a 48V, 35W high power discrete amplifier designed for military communications, radar,
electronic warfare, general purpose broadband amplifier, commercial wireless infrastructure, and
industrial/scientific/Medical applications. Using a second generation advanced high power density Gallium
Nitride (GaN) semiconductor process with improved linearity, these high-performance amplifiers achieve high
efficiency, excellent linearity, and flat gain and power over a broad frequency range in a single amplifier design.
The RFHA3942 is an unmatched GaN transistor, packaged in a hermetic flanged ceramic package. This
package provides excellent thermal stability through the use of advanced heat sink and power dissipation
technologies. Ease of integration is accomplished by incorporating simple, optimized matching networks external
to the package that provide wideband gain and power performance in a single amplifier.
Introduction
The reference design circuit described in this document was designed to achieve a maximum bandwidth, gain
and linearity. A trade off of output power, gain, distortion and efficiency was made. All recommended
components are standard values available from well-known manufacturers. Components specified in the bill of
materials (BOM) have known parasitics, which may affect the circuit’s performance. Deviating from the
recommended BOM or design layout may result in a performance shift due to different parasitics, line
impedances, and line lengths. Component placement, line impedances, and line lengths are critical to each
circuit’s performance.
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
®
AN140228
®
RF MICRO DEVICES and RFMD are trademarks of RFMD, LLC. BLUETOOTH is a trademark owned by Bluetooth SIG, Inc., U.S.A. and licensed for use by RFMD. All other trade names,
trademarks, and registered trademarks are the property of their respective owners. ©2013, RF Micro Devices, Inc.
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RFHA3942 Application Note
Circuit Details
The circuit recommended for this application note was designed using the following PCB material:
• Material: Rogers, RO4350B
• Core thickness: 0.030 inch
• Copper cladding: 1.0oz with plating
• Dielectric constant: 3.48 at 10GHz
• Dissipation Factor: 0.0031 at 2.5GHz
http://www.rogerscorp.com/acm/producttypes/9/RO4000-Laminates.aspx
http://www.rogerscorp.com/acm/products/55/RO4350B-Laminates.aspx
A 0.25” thick copper plate interface was used between device flange and aluminum heat sink.
Aluminum heat sink is Cool Innovations dense pin configuration, 2.5” x 2.5” x 1.7”,
Part number: 3-252517RSF
http://www.coolinnovations.com/
http://www.coolinnovations.com/includes/pdf/heatsinks/3-2525XXRSF.pdf
Design Background Information
As systems move to broadband frequencies of operation, power amplifier designs also are required to do the
same. The output match is required to be the conjugate to the optimum output load of the transistor. Conversely,
the input match is required to be the conjugate to the optimum input impedance of the transistor. One way to
identify how well the circuit match is presented is to measure the reflection coefficient of the match to the
transistor, either as VSWR or return loss. Low value of VSWR or return loss will define how well the circuit
match is to the ideal transistor match.
The following information will describe the fundamental differences of traditional broadband power amplifier
configurations. Additional information on broadband design can be found at
http://www.rfmd.com/cs/documents/CommDRuntonIMS12.pdf
http://www.rfmd.com/cs/documents/hfe0109_bichler.pdf
http://www.rfmd.com/cs/documents/CommSHalderPaperARFTG12.pdf
Cripps, Steve C. (2002) Advanced Techniques in RF Power Amplifier Design. Norwood, MA: Artech House
Grebennikov, Andrei (2005) RF and Microwave Power Amplifier Design. New York, NY: McGraw-Hill
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
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RFHA3942 Application Note
Broadband Amplifier Topologies:
Lumped Element Match
To improve bandwidth, matching circuit should maintain low Q. Multiple elements are typically required for wide
band operations.
Lumped inductor elements can be replaced with micro strip transmission line. As shown with the output match.
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
3 of 14
RFHA3942 Application Note
Transformer Match
A transformer allows a lower impedance matching network. The transformer and transformation ratio would be
determined by the matching impedance of the device, operating power and frequency of the circuit. The
following example shows a 4:1 transformer in use.
Balun Match
A balun allows for a lower impedance matching network. Two parts are driven at 180 degrees using a 1:1 balun.
The matching impedance to each device is dropped in half (25 Ohms in a 50 Ohm system).
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
4 of 14
RFHA3942 Application Note
Combination Transformer/Balun Match
A combination transformer and balun allows for a much lower impedance matching network. Two parts are
driven at 180 degrees using a balun and a 4:1 transformer is added. This results in 6.25 Ohm matching
impedance to the device.
Hybrid Combination
Two or more parts are combined using 90 degree 3dB hybrid couplers to increase power by combining multiple
transistors. This technique does not necessarily lower the required matching impedance, but does allow for
improved S11 and S22. This example requires a match to 50 Ohms.
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
5 of 14
RFHA3942 Application Note
Resistive Feedback
A resistive network is added to the feedback to reduce gain. One drawback is that the output match affects input
impedance and the resistive element must dissipate RF power.
RLC Lossy Input Match
All-pass network at input defines input impedance and gain across frequency of operation.
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
6 of 14
RFHA3942 Application Note
Typical Performance RFHA3942, 500MHz to 2500MHz, 48V, Reference Design
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
7 of 14
RFHA3942 Application Note
Typical Performance RFHA3942, 500MHz to 2500MHz, 48V, Reference Design (continued)
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
8 of 14
RFHA3942 Application Note
Typical Performance RFHA3942, 500MHz to 2500MHz, 48V, Reference Design (continued)
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
9 of 14
RFHA3942 Application Note
Typical Performance RFHA3942, 500MHz to 2500MHz, 48V, Reference Design (continued)
Schematic RFHA3942, 500MHz to 2500MHz, 48V, Reference Design
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
10 of 14
RFHA3942 Application Note
Bill of Materials (BOM) RFHA3942, 500MHz to 2500MHz, 48V, Reference Design
Value
Manufacturer
Manufacturer’s P/N
C1, C10, C18, C23
33pF
ATC
ATC800A330JT
C2, C9
0.3pF
ATC
ATC800A0R3BT
C3, C7
1.5pF
ATC
ATC800A1R5BT
C4
1.7pF
ATC
ATC800A1R7BT
C5
1.8pF
ATC
ATC800A1R8BT
C6
2.7pF
ATC
ATC800A2R7BT
C8
1.0pF
ATC
ATC800A1R0BT
C11
24pF
ATC
ATC800A240JT
C12, C15
0.1µF
Murata
GRM32NR72A104KA01L
C13, C16
4.7µF
Murata
GRM55ER72A475KA01L
C14
100µF
Panasonic
ECE-V1HA101UP
C17
100µF
Panasonic
EEV-TG2A101M
C19, C22
68pF
ATC
ATC800A680JT
C20, C21
100pF
ATC
ATC800A101JT
Item
L1
5nH
Coilcraft
A02T
R1
10Ω
Panasonic
ERJ-8GEYJ100V
RO4350, 0.030" thick dielectric
Rogers
-
PCB
Photo RFHA3942, 500MHz to 2500MHz, 48V, Reference Design
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
11 of 14
RFHA3942 Application Note
Parts Layout RFHA3942, 500MHz to 2500MHz, 48V, Reference Design
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
12 of 14
RFHA3942 Application Note
Bias instructions for the RFHA3942, 500MHz to 2500MHz, 48V, Reference Design
1. Connect RF cables at RFin and RFout
2. Connect ground to the ground supply terminal, and ensure that both the VG and VD grounds are also
connected to this ground terminal
3. Apply -5V to Vgate
4. Apply 48V to Vdrain
5. Increase Vgate until drain current reaches 300mA or desired bias point.
6. Turn on the RF input power
7. Turning the part off is simply the reverse
8. Decrease the Vgate back to -5V
9. Remove the Vdrain
10. Remove the Vgate
Thermal Management
As with most power amplifiers, the circuit must have adequate thermal management in order to operate in an
effective and reliable fashion. An external fan is recommended. Thermal compound is recommended between
flange of the device and heat sink.
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
13 of 14
RFHA3942 Application Note
Mounting Instructions
STEPS FOR MOUNTING A FLANGED DEVICE
1. Heat-sink surface flatness control.
a. Surface finish = average deviation of the mean value of the surface height.
b. Surface roughness (Ra) = 0.8um (0.03mils)
2. A clean interface surface on both the heat-sink and flange.
3. Device mounting holes need to be clean and flat (no burrs).
4. Apply a “thin” and even layer of thermal compound to the surface of the flange.
5. Place the device, “flange-side-down”, into the recess of the PCB.
6. Attach the device to the PBC/Heat-sink with the specified the screw and washer assembly.
(SS #4-40 X ¾ captive SHCS and RND Shim-bearing. .178”O.D. X .123” ID X .01” Thick)
7. Use a Two Step torque sequence:
a. 1st step torque the screw and washer on each side = 0.5kg.cm.
b. 2nd step torque the screw and washer on each side = 6kg.cm (+- 1kg.cm).
Caution: excessive torque may damage the flanged device.
8. Solder the device leads to the PCB.
a. One industry standard is to use a Pb-free alloy (typically SAC305; 96.5%Sn, 3%Ag, 0.5%Cu) with a
liquidus temperature of 221°C.
b.
Temperature at the device lead interface should be <400°C (750F) for <10 seconds.
c.
Pre-tin the leads to reduce any effects of ‘gold embrittlement’.
RF Micro Devices Inc. 7628 Thorndike Road, Greensboro, NC 27409-9421
For sales or technical support, contact RFMD at +1.336.678.5570 or customerservice@rfmd.com.
AN140228
The information in this publication is believed to be accurate. However, no responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any infringement of patents or other rights of
third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent rights of RFMD. RFMD reserves the right to change component circuitry, recommended
application circuitry and specifications at any time without prior notice.
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