Application Measurement Report BLF574 10-550 MHz

Application Measurement Report BLF574 10-550 MHz
CA-212-10
BLF574 at 10-550 MHz
Rev. 3 — 05 October 2015
Application Measurement
Report
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Content
Keywords
BLF574, broadband
Abstract
The BLF574 is a 500 W 50 V LDMOS RF power push-pull transistor for
broadcast transmitter and industrial applications from HF to 500 MHz. This
test report describes a broadband amplifier that delivers more than 400 W
from 20 to 550 MHz.
CA-212-10
BLF574 at 10-550 MHz
Revision history
Rev
Date
Description
1
20150626
Initial version
2
20150626
Preparation for online publication
3
20151005
The format of this document has been redesigned to comply with the new identity
guidelines of Ampleon.
Legal texts have been adapted to the new company name where appropriate.
CA-212-10
Application Measurement Report
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 05 October 2015
© Ampleon B.V. 2015. All rights reserved.
2 of 17
CA-212-10
BLF574 at 10-550 MHz
1. Introduction
The BLF574 is a 500 W LDMOS RF power push-pull transistor for broadcast transmitter and industrial
applications from HF to 500 MHz. This report describes a broadband amplifier which delivers more than 400
W from 20 to 550 MHz.
Fig 1. BLF574 10-550 MHz 400 W amplifier
2. Summary
The RF performance described in chapter 3 may be summarized as follows:
Specified frequency range
10 to 550 MHz
Specified drain voltage
50 V
Quiescent drain current
1A
Input return loss
≥ 5 dB; 10 dB typ
CW output power
≥ 400 W, 20 to 550 MHz
≥ 300 W, 10 to 20 MHz
Gain
≥ 20 dB, 10 to 300 MHz
≥ 16 dB, 300 to 550 MHz
Gain flatness
3 dB, 10 to 300 MHz
Efficiency at 400 W
≥ 46%; 55% typ
IMD3 at 400 W PEP
-35 dBc typ
Table 1.
Summary of RF performance
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Application Measurement Report
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BLF574 at 10-550 MHz
3. RF performance
Fig 2. Test setup for RF performance measurements
3.1 1-Tone CW
Fig 3. PL(3dB)
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BLF574 at 10-550 MHz
Fig 4. Small-signal power gain
Fig 5. Gain and efficiency for PL = 10 W
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BLF574 at 10-550 MHz
Fig 6. Gain and efficiency for PL = 100 W
Fig 7. Gain and efficiency for PL = 300 W
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Application Measurement Report
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BLF574 at 10-550 MHz
Fig 8. Gain and efficiency for PL = 400 W
Fig 9. Power gain and drain efficiency for VD = 50 V
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BLF574 at 10-550 MHz
Fig 10. Power gain and drain efficiency for VD = 43 V
Fig 11. Input return loss
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Application Measurement Report
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BLF574 at 10-550 MHz
Fig 12. 2nd and 3rd harmonic levels for PL = 10 and 100 W
Note that the measured 2nd harmonic levels are at the system test limit, so the actual levels may be
significantly lower.
3.2 2-Tone CW
Fig 13. 2-tone power gain and efficiency
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BLF574 at 10-550 MHz
Fig 14. Third-order intermodulation distortion
3.3 Input matching
The BLF574 has a rather large Ciss of more than 200 pF. To provide a broadband input match to the device at
higher frequencies, it is necessary to present a source impedance that is rather lower than the optimal
impedance at middle and lower frequencies. This is provided by a 16:1 input network (two cascaded 4:1
transformers), which present a differential source impedance of approximately 3 Ω.
3.4 Feedback
Resistive feedback is used to flatten gain at lower frequencies. With the optimized broadband input and output
networks, the open-loop gain is approximately 20 dB at 300 MHz. The gain at lower frequencies can be
reduced to 20 dB with 50 Ω feedback resistors; but this has a significant effect on efficiency, and naturally
does nothing to increase gain above 300 MHz.
3.5 Output matching
The output 1:4 transmission line transformer (TLT) presents a differential load resistance of approximately 12.5
Ω to the device, which is about as close as we can get with a physically realizable broadband network to the 10
Ω RLOAD estimate given by Cripp's load line approximation of 2 · (50V - 5V)2 I (2 · 200W). The amplifier was
tested with a 1:9 TLT in an attempt to produce higher peak powers; but because the lower load resistance
results in a lower efficiency, peak power ends up being limited by junction temperature rather than output
voltage clipping.
CA-212-10
Application Measurement Report
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BLF574 at 10-550 MHz
Fig 15. Gain and efficiency with 1:4 and 1:9 output transformers
The final 400 W amplifier uses a 1:4 output transformer constructed with 15 Ω semi-rigid coax. Using cable
with a characteristic impedance of 15 Ω (instead of 25 Ω) provides a better match above 300 MHz, providing
slightly better gain (1 dB) and significantly better efficiency (53% vs. 38% for POUT = 400 W at 550 MHz with
VD = 50 V).
CA-212-10
Application Measurement Report
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Rev. 3 — 05 October 2015
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BLF574 at 10-550 MHz
3.6 Thermal considerations
Because multi-octave broadband amplifiers necessarily trade off optimal source and load impedance matching
for bandwidth, and use resistive feedback to flatten low-frequency gain, they are always less efficient than
sub-octave designs. Since the device has to dissipate significantly more power, device cooling is
correspondingly more critical than with higher-efficiency narrowband applications.
In addition, the feedback resistors and the ferrite cores in the transmission line transformers also dissipate
significant amounts of power (both of which vary with frequency) which has to be removed efficiently.
The prototype design showed that the 0.23 KIW Rth(j-c) of the non-thermally-enhanced SOT539A package used
for the BLF574 was the main limitation to the device's ability to deliver peak broadband power above 300 W.
To keep the device as cool as possible, a liquid-cooled baseplate was used, with a high-conductivity thermal
interface compound (Bergquist TIC4000) between the device and the baseplate.
The feedback resistors are cooled by being bolted to the flanges of the BLF574, while the ferrite cores are
attached to the baseplate with thermally conductive epoxy.
Fig 16 shows the temperatures of the BLF574 junction (calculated from measurements made with a
thermocouple connected through the baseplate to the center of the device flange) and the transformers' ferrite
cores at the most inefficient frequency (300 MHz). This shows that safe continuous operation is possible
above 400 W.
Fig 16. Gain and efficiency with 1:4 and 1:9 output transformers
CA-212-10
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Rev. 3 — 05 October 2015
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BLF574 at 10-550 MHz
5. PCB information
Fig 17. PCB layout
Fig 18. RF schematic
CA-212-10
Application Measurement Report
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Rev. 3 — 05 October 2015
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BLF574 at 10-550 MHz
Table 2.
RF circuit bill of materials
Fig 19. Output transformer semi-rigid cables, 1:1 scale
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Application Measurement Report
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Rev. 3 — 05 October 2015
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BLF574 at 10-550 MHz
Fig 20. Bias circuit schematic
Table 3.
Bias circuit bill of materials
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Application Measurement Report
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 05 October 2015
© Ampleon B.V. 2015. All rights reserved.
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BLF574 at 10-550 MHz
6. Legal information
such equipment or applications and therefore such inclusion and/or use is at
the customer’s own risk.
6.1 Definitions
Draft — The document is a draft version only. The content is still under
internal review and subject to formal approval, which may result in
modifications or additions. Ampleon does not give any representations or
warranties as to the accuracy or completeness of information included herein
and shall have no liability for the consequences of use of such information.
6.2 Disclaimers
Limited warranty and liability — Information in this document is believed to
be accurate and reliable. However, Ampleon does not give any
representations or warranties, expressed or implied, as to the accuracy or
completeness of such information and shall have no liability for the
consequences of use of such information. Ampleon takes no responsibility
for the content in this document if provided by an information source outside
of Ampleon.
In no event shall Ampleon be liable for any indirect, incidental, punitive,
special or consequential damages (including - without limitation - lost profits,
lost savings, business interruption, costs related to the removal or
replacement of any products or rework charges) whether or not such
damages are based on tort (including negligence), warranty, breach of
contract or any other legal theory.
Notwithstanding any damages that customer might incur for any reason
whatsoever, Ampleon’s aggregate and cumulative liability towards customer
for the products described herein shall be limited in accordance with the
Terms and conditions of commercial sale of Ampleon.
Right to make changes — Ampleon reserves the right to make changes to
information published in this document, including without limitation
specifications and product descriptions, at any time and without notice. This
document supersedes and replaces all information supplied prior to the
publication hereof.
Suitability for use — Ampleon products are not designed, authorized or
warranted to be suitable for use in life support, life-critical or safety-critical
systems or equipment, nor in applications where failure or malfunction of an
Ampleon product can reasonably be expected to result in personal injury,
death or severe property or environmental damage. Ampleon and its
suppliers accepts no liability for inclusion and/or use of Ampleon products in
Applications — Applications that are described herein for any of these
products are for illustrative purposes only. Ampleon makes no representation
or warranty that such applications will be suitable for the specified use
without further testing or modification.
Customers are responsible for the design and operation of their applications
and products using Ampleon products, and Ampleon accepts no liability for
any assistance with applications or customer product design. It is customer’s
sole responsibility to determine whether the Ampleon product is suitable and
fit for the customer’s applications and products planned, as well as for the
planned application and use of customer’s third party customer(s).
Customers should provide appropriate design and operating safeguards to
minimize the risks associated with their applications and products.
Ampleon does not accept any liability related to any default, damage, costs
or problem which is based on any weakness or default in the customer’s
applications or products, or the application or use by customer’s third party
customer(s). Customer is responsible for doing all necessary testing for the
customer’s applications and products using Ampleon products in order to
avoid a default of the applications and the products or of the application or
use by customer’s third party customer(s). Ampleon does not accept any
liability in this respect.
Export control — This document as well as the item(s) described herein
may be subject to export control regulations. Export might require a prior
authorization from competent authorities.
6.3 Trademarks
Notice: All referenced brands, product names, service names and
trademarks are the property of their respective owners.
Any reference or use of any ‘NXP’ trademark in this document or in or on the
surface of Ampleon products does not result in any claim, liability or
entitlement vis-à-vis the owner of this trademark. Ampleon is no longer part
of the NXP group of companies and any reference to or use of the ‘NXP’
trademarks will be replaced by reference to or use of Ampleon’s own
trademarks.
6.4 Contact information
For more information, please visit: http://www.ampleon.com
For sales office addresses, please visit: http://www.ampleon.com/sales
CA-212-10
Application Measurement Report
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 05 October 2015
© Ampleon B.V. 2015. All rights reserved.
16 of 17
CA-212-10
BLF574 at 10-550 MHz
7. Contents
1.
2.
3.
3.1
3.2
3.3
3.4
3.5
3.6
5.
6.
6.1
6.2
6.3
6.4
7.
Introduction ......................................................... 3
Summary .............................................................. 3
RF performance ................................................... 4
1-Tone CW ......................................................... 4
2-Tone CW ......................................................... 9
Input matching.................................................. 10
Feedback ......................................................... 10
Output matching ............................................ 10
Thermal considerations ................................. 12
PCB information.............................................. 13
Legal information .............................................. 16
Definitions ........................................................ 16
Disclaimers....................................................... 16
Trademarks ...................................................... 16
Contact information .......................................... 16
Contents ............................................................. 17
Please be aware that important notices concerning this document and the product(s)
described herein, have been included in the section 'Legal information'.
© Ampleon B.V. 2015.
All rights reserved.
For more information, please visit: http://www.ampleon.com
For sales office addresses, please visit: http://www.ampleon.com/sales
Date of release: 05 October 2015
Document identifier: CA-212-10
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