BFU520X ISM 866 MHz LNA design

AN11434
BFU520X ISM 866 MHz LNA design
Rev. 1 — 05 December 2013
Application note
Document information
Info
Content
Keywords
BFU520, BFU530, BFU550 series, ISM-band, 433MHz 866MHz
Abstract
This document describes an ISM Frequency LNA design on BFU5xxX
Starter kit
Ordering info
BFU5xxX Starter kit OM7963, 12nc 9340 678 72598
Contact information
For more information, please visit: http://www.nxp.com
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Example LNA design using BFU520X
Revision history
Rev
Date
Description
1
20140124
First publication
Contact information
For more information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: [email protected]
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1. Abstract
In this application note an ISM band (industrial, scientific and medical) LNA design (low noise amplifier)
using a BFU5xx transistor from NXP latest wideband transistor range is described. It shows the design,
simulation and implementation phases. Together with measurement results, parameters measured over
temperature are shown.
The application note (AN) can be a starting point for new design(s), and/or derivative designs.
2. Introduction
The BFU5xxX transistor family is designed to meet the latest requirements on high frequency applications
(up to approximately 2 GHz) such as communication, automotive and industrial equipment.
As soon as fast, low noise analogue signal processing is required, combined with medium to high voltage
swings the BFU5xxX transistors are the perfect choice. Due to the high gain at low supply current those
types can also be applied very well in battery powered equipment.
Compared to previous Philips / NXP transistor generations and competitor products’ improvements on
gain, noise and thermal properties are realized. BFU5xxX transistors are available in various packages.
The transistors are promoted with a full promotion package, called “starter kits” (one kit type per packagetype). Those kits include two PCB’s (one with grounded emitter, one with emitter degeneration provision),
RF connectors, transistors and simulation model parameters required to perform simulations. See the
overview of available starter kits in the table below.
Table 1.
Customer evaluation kits
Basic type
Customer evaluation kits
1
BFU520W, BFU530W, BFU550W
OM7960, starter kit for transistors in SOT323 package
2
BFU520A, BFU530A, BFU550A
OM7961, starter kit for transistors in SOT23 package
3
BFU520, BFU530, BFU550
OM7962, starter kit for transistors in SOT143 package
4
BFU520X, BFU530X, BFU550X
OM7963, starter kit for transistors in SOT143X package
5
BFU520XR, BFU530XR, BFU550XR
OM7964, starter kit for transistors in SOT143XR package
6
BFU580Q, BFU590Q
OM7965, starter kit for transistors in SOT89 package
7
BFU580G, BFU590G
OM7966, starter kit for transistors in SOT223 package
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Basic type
Customer evaluation kits
Fig 1. BFU5xxX evaluation boards
3. Requirements
The demonstrator circuit is designed to show the BFU520X capabilities for a 866 MHz ISM LNA with
strong focus on best possible Noise Figure at low to medium supply current.
The aim of the demonstrator circuit was to design a LNA optimized for the ISM band for battery powered
equipment meeting following requirements:
Supply Voltage:
3.6 Volts nominal
Supply current:
7mA at ambient temperature
Noise Figure:
< 1.2dB
Gain:
approx. 17dB
OIP3:
priority on NF but preferably >+10dBm
Input Return-Loss: < -8dB
Output Return-Loss: < -10dB
The design is aimed at low BOM cost and small PCB area, inductors are SMD types (preferable low cost
multilayer types) to enable simple tuning to other frequency bands.
4. Design considerations
In order to achieve minimum Noise Figure, with Gain still close to the maximum available gain, the source
impedance has to be close to the optimum for Noise Figure and not too far from to the maximum gain
impedance. Designing for optimum Noise Figure will compromise, for example, the input return loss, but
this is assumed to be acceptable.
At any time the circuit should be stable, hence during the design phase the K-factor needs to be observed
carefully.
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5. Design approach
The design starts in the simulation phase, applying the Mextram Model (available at http://www.nxp.com).
Agilent “Advanced Design System” (ADS) was used for this but other simulation software packages
should give equal results. Spice / Gummel Poon models are available.
Once simulation results meet the requirements, the circuit is built on a universal Printed Circuit Board
(PCB) and evaluated. If measurement results show significant offset from simulated results, fine tuning is
required until required performance is met. To achieve better matching between simulations and
measurements, the PCB parasitic properties were added in the simulation template.
Following blocks of passive components can be identified:
1) resistors for DC biasing
2) passives set up collector load
3) passives for output matching
4) passives for input matching
5) passives required to ensure stable operation
Each block will be discussed separately below.
5.1 Simulation steps
Following simulation / design approach can be useful:
1) Configure the DC bias set-up, ensuring the Icc is set around desired value.
2) Configure the collector load circuit and output matching circuitry, optimizing the output Return
Loss (RL).
3) Check stability.
4) Configure the input matching, for LNA optimize for minimum noise figure (NF) but keep close to
optimum gain, if possible optimum NF gain points should be close.
5) Check stability.
Assumptions:
-
Realistic passives are used by applying Murata design kit (0603 / 0402)
-
PCB tracks represented by strip-lines
5.2 Implementation / evaluation steps
Following implementation / evaluation steps have been executed:
1) Implement simulated design on universal PCB.
2) Evaluate LNA on Gain / NF / matching / Stability at ambient temperature.
3) Fine tune passives if required.
4) In case significant differences between simulations and measured results are observed, try to
modify parasitic properties in the simulation template.
5) Measure LNA design on RF parameters over temperature.
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5.3 Setting up the DC bias circuit
Vcc
Vcc
C2
C2
R3
R3
C3
C3
R1
R2
R1
Lcol
R2
Lcol
C1
Lbase
DC bias circuit 2
DC bias circuit 1
Fig 2. Circuitry to set DC bias current
Circuit 1 has the advantage that resistive noise from the resistors R1 and R2 is suppressed by capacitor
C1, but at the cost of an extra inductor. This inductor can be part of the input matching.
Circuit 2 is commonly used and saves two passive components. Both circuits tend to have increasing
collector current (Icc) with increasing temperature, partly stabilized by R3. Increasing R3 will have impact
on the linearity (OIP3, P1dB).
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5.4 Definition of collector load and output match
The configuration used and simulation display is shown below (ADS).
Fig 3. ADS design template for output stage design
In this simulation for the 866 MHz ISM Band the input matching circuit is bypassed. The components L18,
C46, C47 are tuned to get a match in the required frequency band.
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Fig 4. ADS simulation results for transistor + bias + output match
After defining the configuration for the collector load / output matching network and tuning the component
values, a simulation is executed to observe the amplifiers stability. See figure below.
Fig 5. ADS simulation results for stability (µ-factor)
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5.5 Definition of input / source matching circuit
In case the amplifier has to be designed to get minimum noise figure, the “noise and gain circles” can be
applied.
See figure below: In the noise circles plot you can find the area for optimum source impedance, as should
be seen by the base of the transistor, to achieve lowest noise figure.
Fig 6. BFU520X Noise and Gain circles at 866 MHz
This is the result from simulations of the set-up as shown in section 5.4, Fig 3.
In this Smith Chart you can find the optimum load impedance for optimum noise in the smallest blue
circle, NF 0.76dB (this is the expected NF for the transistor without matching/PCB losses). In case the
source impedance is shifted into the region of the second blue circle, the NF will be increased by
approximately 0.2dB.
The same applies to the Gain, but in that case the red circles needs to be considered.
The input matching network needs to be set up such that the source impedance as seen by the transistor
is close to the optimum for NF, preferably also close to optimum gain circle.
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In the next figure the simulation template to optimize for best source impedance is shown. Please note
that the active part of the circuit is bypassed. We want to observe the S22 which is the source impedance
for the transistor applied.
Fig 7. ADS simulation template for input matching
By tuning the components L19, C38 you could move the source impedance towards required area.
Fig 8. ADS simulation results for source matching
From this figure we see the source impedance at 866 MHz is in the area we want.
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5.6 Overall LNA simulation
ADS template used:
Fig 9. BFU520X 866 MHz LNA simulation
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Simulation results:
Fig 10. BFU520X 866 MHz LNA simulation results, S-parameters/ DC biasing
S-parameters at 3.6 Volt.
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Fig 11. BFU520X 866 MHz LNA simulations, Noise / Gain circles
Compared to the noise circles of the unmatched circuit (section 5.5), we can clearly see the
optimum noise point has moved towards the ideal 50R point.
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6. Application circuit
The circuit diagram of the evaluation board is shown in Fig 12 PCB schematic.
6.1 BFU520X 866 MHz ISM LNA schematic
Fig 12. Schematic as implemented for measurements
The PCB layout used for our internal evaluations did not accommodate the 15nH inductor to be in the bias
path (as shown in the ADS schematics). The input matching inductor was placed to ground (GND) and an
additional DC blocking capacitor (82pF) was used. This should give equal results at the cost of a slight
degradation in the Noise Figure (approx. 0.05dB).
Please note that not-used components (0R or jumpers that are present on the PCB design to allow
different input configurations) in series with the signal path at the LNA input might cause additional input
loss that adds to the Noise Figure.
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6.2 BFU520X 866 MHz ISM LNA PCB drawing
Vcc
NM
GND
Vcc
GND
8.2nH
NM
2.7p
0R
NM
NM
NM
8k2
82p
15nH
NM
18p
0R
6.8p
BFU520X
0R
5.6n
220p
0R
NM
3k3
NM
22R
2R2
27p
Fig 13. PCB implementation for measurements
Remarks:
0R = SMD jumper
NM = component not mounted.
This layout, as delivered with the Starter kit, accommodates the possibility to implement the biasing as
shown in the ADS schematics.
6.3 PCB properties, layer stack
Fig 14. PCB layers used for Evaluation Boards in Starter kit
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6.1 Typical LNA evaluation board results
Table 2. Typical results measured on the evaluation boards
Operating Frequency is f = 866 MHz unless otherwise specified; Temp = 25 °C
Parameter
Symbol
EVB
Unit
Remarks
Supply Voltage
VCC
3.6
V
Supply Current
ICC
7
mA
Noise Figure
NF
1.1
dB
Power Gain
Gp
16
dB
Input Return Loss
RLin
-8
dB
Output Return Loss
RLout
-12
dB
Output third order
intercept point
OIP3
14
dBm
Table 3. Bill Of Materials
Value
Description
Footprint
Manufacturer
BFU520X
Transistor
SOT143X
NXP Semiconductors
2.7 pF
Capacitor
0603
Various
6.8 pF
Capacitor
0603
Various
18 pF
Capacitor
0603
Various
27 pF
Capacitor
0603
Various
82 pF
Capacitor
0603
Various
220 pF
Capacitor
0603
Various
5.6 nF
Capacitor
0603
Various
2.2 Ω
Resistor
0603
Various
22 Ω
Resistor
0603
Various
3.3 kΩ
Resistor
0603
Various
8.2 kΩ
Resistor
0603
Various
8.2 nH
Inductor
0603
Murata LQW18A
15 nH
Inductor
0603
Murata LQW18A
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7. Characterization of LNA over temperature and supply voltage
7.1 Gain (S21) = f (freq)
7.2 Input return-loss (S11) = f (freq)
20
|S21|^2
(dB)
0
|S11|^2
18
(dB)
16
14
-5
-10
12
-15
10
8
-20
6
4
-25
2
0
600
700
800
900
1000
-30
Application note
700
800
900
Vsup = 3.6 V; Tamb = -40 °C
Tamb = -40 °C
Fig9. Gain
Tamb
= 25 as
°C a function of frequency; typical values
Tamb = 85 °C
Tamb = 125 °C
Vsup = 3.6 V; Tamb = -40 °C
Tamb = -40 °C
Fig9. Gain
Tamb
= 25 as
°C a function of frequency; typical values
Tamb = 85 °C
Tamb = 125 °C
Insertion power gain as a function of frequency; typical values
Input return loss as a function of frequency; typical values
Fig 15. Measured S21 over frequency for different temperatures
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1000
Frequency (MHz)
Frequency (MHz)
Fig 16. Measured S11 over frequency for different temperatures
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7.3 Output return-loss (S22) = f (freq)
7.4 Isolation (S12) = f (freq)
0
-10
|S22|^2
(dB)
|S12|^
(dB)
2
-5
-15
-20
-25
-10
-30
-15
-35
-40
-20
-45
-50
-25
-55
-30
600
700
800
900
1000
-60
600
Frequency (MHz)
Application note
800
900
Vsup = 3.6 V; Tamb = -40 °C
Tamb = -40 °C
Fig9. Gain
Tamb
= 25 as
°C a function of frequency; typical values
Tamb = 85 °C
Tamb = 125 °C
Output return loss as a function of frequency; typical values
Isolation as a function of frequency; typical values
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1000
Frequency (MHz)
Vsup = 3.6 V; Tamb = -40 °C
Tamb = -40 °C
Fig9. Gain
Tamb
= 25 as
°C a function of frequency; typical values
Tamb = 85 °C
Tamb = 125 °C
Fig 17. Measured S22 over frequency for different temperatures
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Fig 18. Measured S12 over frequency for different temperatures
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7.5 Output third-order intercept point (OIP3) = f (Tamb)
7.6 Output Power at 1 dB compression (P1dB) = f (Tamb)
5
20
IP3O
(dBm)
PL(1dB)
(dBm)
15
0
10
-5
5
-10
0
-15
-5
-50
0
50
100
150
-20
-50
Tamb (°C)
f1=433MHz, f2=433.1MHz
Vsup = 3.2 V
Vsup = 3.6 V
Vsup = 4.0 V
Fig 19. Measured OIP3 over temperature for different supply voltages
Application note
50
100
150
Tamb (°C)
Vsup = 3.2 V
Vsup = 3.6 V
Vsup = 4.0 V
Third order intercept point as a function of ambient temperature;
typical values
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Ouput power at 1dB gain compression as a function of ambient
temperature; typical values
Fig 20. Measured 1dB compression point over temperature for different
supply voltages
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7.7 Noise Figure = f (Freq)
2.5
NF
(dB)
2.3
2.1
1.9
1.7
1.5
1.3
1.1
0.9
0.7
0.5
840
850
860
870
880
890
Frequency (MHz)
Vsup = 3.6 V; Tamb = -40 °C
Tamb = -40 °C
Fig9. Gain
Tamb
= 25 as
°C a function of frequency; typical values
Tamb = 85 °C
Tamb = 125 °C
NF as a function of frequency; typical values
Fig 21. Measured Noise Figure over temperature for different supply
voltages
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8. Conclusions / recommendations
With BFU520X a ISM 866 MHz LNA design with NF close to 1.2dB can be implemented, for this the
input return loss has to be compromised. The circuit can be used as a base for derivative designs,
matching to other frequencies can be done by tuning relevant capacitors and inductors.
For improvements on linearity it could be recommended to increase the DC biasing current and increase
values for decoupling capacitors to GND, for example on the biasing network in case the matching
inductor is in the configuration as shown in the ADS schematics.
BFU520 series
Lowest Noise at low supply current
Low Noise and medium Linearity
Low Noise and high Linearity, high Icc
BFU530 series
BFU550 series
x
x
x
8.1 Tuning the design for other frequencies
This LNA can be tuned to other frequencies as well. The presented configuration has been designed for a
low bandwidth application (Center frequency/required bandwidth = approx 10-100 depending on the used
components).
The LNA can be tuned to other frequencies following section 5.4 till 5.6. The use of printed inductors or
micro-strip elements is recommended above 1GHz to prevent gain drop.
For wideband amplifiers a feedback is recommended which can be implemented on the existing board.
A reference design for a wideband amplifier, applying feedback, is planned to be issued. Please regularly
visit the NXP PIP pages to monitor availability of BFU5- series related AN’s.
9. References
BFU520X datasheet
BFU5xxX starter-kit (OM7963) User Manual, UM10772
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10. Legal information
10.1 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. NXP Semiconductors 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.
10.2 Disclaimers
Limited warranty and liability — Information in this document is
believed to be accurate and reliable. However, NXP Semiconductors
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. NXP
Semiconductors takes no responsibility for the content in this document
if provided by an information source outside of NXP Semiconductors.
In no event shall NXP Semiconductors 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, NXP Semiconductors’ 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 NXP
Semiconductors.
Right to make changes — NXP Semiconductors 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 — NXP Semiconductors 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 NXP Semiconductors product can reasonably be
expected to result in personal injury, death or severe property or
environmental damage. NXP Semiconductors and its suppliers accept
no liability for inclusion and/or use of NXP Semiconductors products in
such equipment or applications and therefore such inclusion and/or use
is at the customer’s own risk.
Applications — Applications that are described herein for any of these
products are for illustrative purposes only. NXP Semiconductors 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 NXP Semiconductors products, and
NXP Semiconductors accepts no liability for any assistance with
applications or customer product design. It is customer’s sole
responsibility to determine whether the NXP Semiconductors 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.
NXP Semiconductors 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
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herein may be subject to export control regulations. Export might require
a prior authorization from national authorities.
Evaluation products — This product is provided on an “as is” and “with
all faults” basis for evaluation purposes only. NXP Semiconductors, its
affiliates and their suppliers expressly disclaim all warranties, whether
express, implied or statutory, including but not limited to the implied
warranties of non-infringement, merchantability and fitness for a
particular purpose. The entire risk as to the quality, or arising out of the
use or performance, of this product remains with customer.
In no event shall NXP Semiconductors, its affiliates or their suppliers be
liable to customer for any special, indirect, consequential, punitive or
incidental damages (including without limitation damages for loss of
business, business interruption, loss of use, loss of data or information,
and the like) arising out the use of or inability to use the product, whether
or not based on tort (including negligence), strict liability, breach of
contract, breach of warranty or any other theory, even if advised of the
possibility of such damages.
Notwithstanding any damages that customer might incur for any reason
whatsoever (including without limitation, all damages referenced above
and all direct or general damages), the entire liability of NXP
Semiconductors, its affiliates and their suppliers and customer’s
exclusive remedy for all of the foregoing shall be limited to actual
damages incurred by customer based on reasonable reliance up to the
greater of the amount actually paid by customer for the product or five
dollars (US$5.00). The foregoing limitations, exclusions and disclaimers
shall apply to the maximum extent permitted by applicable law, even if
any remedy fails of its essential purpose.
10.3 Trademarks
Notice: All referenced brands, product names, service names and
trademarks are property of their respective owners.
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11. List of figures
Fig 1.
Fig 2.
Fig 3.
Fig 4.
Fig 5.
Fig 6.
Fig 7.
Fig 8.
Fig 9.
Fig 10.
Fig 11.
Fig 12.
Fig 13.
Fig 14.
Fig 15.
Fig 16.
Fig 17.
Fig 18.
Fig 19.
Fig 20.
Fig 21.
BFU5xxX evaluation boards ..............................4
Circuitry to set DC bias current .........................6
ADS design template for output stage design ...7
ADS simulation results for transistor + bias + output
match ................................................................8
ADS simulation results for stability (µ-factor) ....8
BFU520X Noise and Gain circles at 866 MHz...9
ADS simulation template for input matching.... 10
ADS simulation results for source matching .... 10
BFU520X 866 MHz LNA simulation ................ 11
BFU520X 866 MHz LNA simulation results, Sparameters/ DC biasing .................................. 12
BFU520X 866 MHz LNA simulations, Noise / Gain
circles .............................................................. 13
Schematic as implemented for measurements14
PCB implementation for measurements .......... 15
PCB layers used for Evaluation Boards in Starter kit
........................................................................ 15
Measured S21 over frequency for different
temperatures ................................................... 17
Measured S11 over frequency for different
temperatures ................................................... 17
Measured S22 over frequency for different
temperatures ................................................... 18
Measured S12 over frequency for different
temperatures ................................................... 18
Measured OIP3 over temperature for different
supply voltages ............................................... 19
Measured 1dB compression point over temperature
for different supply voltages ............................ 19
Measured Noise Figure over temperature for
different supply voltages ................................. 20
AN11434
Application note
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 24 January 2014
© NXP B.V. 2014. All rights reserved.
23 of 25
AN11434
NXP Semiconductors
Example LNA design using BFU520X
12. List of tables
Table 1.
Table 2.
Table 3.
Customer evaluation kits ...................................3
Typical results measured on the evaluation boards
........................................................................ 16
Bill Of Materials ............................................... 16
AN11434
Application note
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 24 January 2014
© NXP B.V. 2014. All rights reserved.
24 of 25
AN11434
NXP Semiconductors
Example LNA design using BFU520X
13. Contents
1.
2.
3.
4.
5.
5.1
5.2
5.3
5.4
5.5
5.6
6.
6.1
6.2
6.3
6.1
7.
7.1
7.2
7.3
7.4
7.5
7.6
7.7
8.
8.1
9.
10.
10.1
10.2
10.3
11.
12.
13.
Abstract ................................................................3
Introduction..........................................................3
Requirements.......................................................4
Design considerations ........................................4
Design approach .................................................5
Simulation steps .................................................5
Implementation / evaluation steps ......................5
Setting up the DC bias circuit .............................6
Definition of collector load and output match ......7
Definition of input / source matching circuit ........9
Overall LNA simulation ..................................... 11
Application circuit ............................................. 14
BFU520X 866 MHz ISM LNA schematic .......... 14
BFU520X 866 MHz ISM LNA PCB drawing ..... 15
PCB properties, layer stack .............................. 15
Typical LNA evaluation board results ............... 16
Characterization of LNA over temperature and
supply voltage ................................................... 17
Gain (S21) = f (freq) ......................................... 17
Input return-loss (S11) = f (freq) ....................... 17
Output return-loss (S22) = f (freq) .................... 18
Isolation (S12) = f (freq).................................... 18
Output third-order intercept point (OIP3) = f (Tamb)
......................................................................... 19
Output Power at 1 dB compression (P1dB) = f
(Tamb) .............................................................. 19
Noise Figure = f (Freq) ..................................... 20
Conclusions / recommendations ..................... 21
Tuning the design for other frequencies ........... 21
References ......................................................... 21
Legal information .............................................. 22
Definitions......................................................... 22
Disclaimers ....................................................... 22
Trademarks ...................................................... 22
List of figures ..................................................... 23
List of tables ...................................................... 24
Contents ............................................................. 25
Please be aware that important notices concerning this document and the product(s)
described herein, have been included in the section 'Legal information'.
© NXP B.V. 2014.
All rights reserved.
For more information, visit: http://www.nxp.com
For sales office addresses, please send an email to: [email protected]
Date of release: 24 January 2014
Document identifier: AN11434
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