Post on 20-Apr-2015
GaN Power Amplifier Design
using ADS2011
Anurag Bhargava
Application Consultant
Agilent EEsof EDA
Agilent Technologies
Email: anurag_bhargava@agilent.com
You Tube: www.youtube.com/user/BhargavaAnurag
Blog: http://abhargava.wordpress.com
Outline
• Introduction
• DC and Loadline analysis
• Bias and Stability
• LoadPull
• Matching using Smith Chart Utility
• SourcePull (Optional Step)
• PA Characterization – Did we meet the specification?
• Optimize/Fine Tune the design
• Test Design with real world modulated signals
Why do we need a Power Amplifier?
OSC
MODBaseband PADriver
Basic Transmitter
Power Amplifiers (PA) are in the transmitting chain of a wireless
system. They are the final amplification stage before the signal is
transmitted, and therefore must produce enough output power to
overcome channel losses between the transmitter and the receiver.
PA requirements
• The PA is typically the primary consumer of power in a transmitter. A major design
requirement is how efficiently the PA can convert DC power to RF output power.
• The design engineer has to often concern himself with the Efficiency of the Power
Amplifier. Notice that efficiency translates into either lower operation cost (e.g.
cellular base station) or longer battery life (e.g. wireless handheld).
• PA linearity is another important requirement, the input/ output relationship must
be linear to preserve the signal integrity.
• The design of PAs often involves the tradeoff of efficiency and linearity.
Non-Linear model?
Good PA design starts with good Non-Linear device model and it is device
vendor’s responsibility to provide good non-linear model to PA designers.
There are various ways in which vendor can provide non-linear model:
a. SPICE model (can be imported into ADS)
b. Non-Linear model card i.e. provide parameters for standard model cards such as
Curtice Cubic, Statz, BSIM etc (can be used directly in ADS)
c. Design Kit for ADS containing the non-linear models (usually encrypted)
Non-Linear Model
In absence of Non-Linear model, following approaches can be used:
Approach 1: Integrated Circuit
Characterization and Analysis
Program (ICCAP)
• Powerful characterization and analysis
capabilities for a broad range of
semiconductor modeling processes.
• Includes instrument control, data
acquisition, graphical analysis,
simulation, optimization, and statistical
analysis.
• IC-CAP Extraction Packages provide
an automated procedure to measure
and extract a particular model (BSIM4,
PSP, HiSim HV, CMOS)
Measure X-parameters
-or-
Generate X-parameters from
circuit-level designs
X-parameter Component :
Simulate using X-
parameters
ADS, SystemVue & Genesys:
Design using X-parameters
Approach 2: X-parameters revolutionize the
Characterization, Design, and Modeling of nonlinear
components and systems
X-parameters are the mathematically correct extension of S-
parameters to large-signal conditions.
• Measurement and simulation based, device independent, identifiable from a simple
set of automated NVNA measurements or directly from ADS circuit-level designs
• Fully nonlinear (Magnitude and phase of distortion)
• Cascadable (correct behavior in even highly mismatched environment)
• Extremely accurate for high-frequency, distributed nonlinear devices
Evolution of the Tools & Measurements
TOOLS:
NA
SA/SS/NFA
Power meter
Oscilloscope
DC Parametric Analyzer
MEASUREMENTS:
Gain compression, IP3, IMD
PAE, ACPR, AM-PM, BER
Constellation Diagram, EVM
GD, NF, Spectral Re-growth
ACLR, Hot “S22”
Source and Load-Pull
S-Parameters
TOOLS:
Vector Network
Analyzer
MEASUREMENTS:
Gain
Input match
Output match
Isolation
Transconductance
Input capacitance
S-Parameters +
Figures of Merit
TOOLS:
SS & Oscilloscope
Grease pens and
Polaroid cameras
Slotted line
Power meter
MEASUREMENTS:
Bode plots
Gain
SWR
Scalar network analyzers
Y & Z parameters
Patchwork NVNA
X-Parameters
High Power X-parameter Measurement System
Nonlinear Vector Network Analyzer (NVNA) Vector (amplitude/phase) corrected nonlinear
measurements from 10 MHz to 13.5, 26.5 43.5 50 GHz
Calibrated absolute amplitude and relative phase (cross-
frequency relative phase) of measured spectra traceable to
standards lab
Up to 50 GHz of vector corrected bandwidth for time
domain waveforms of voltages and currents of DUT
Multi-Envelope domain measurements for measurement
and analysis of memory effects
X-parameters: Extension of Scattering parameters into the
nonlinear region providing unique insight into nonlinear DUT
behavior
X-parameter extraction into ADS nonlinear simulation and
design
NVNA can control external DC instruments (sweep and
sense) during RF measurements
Standard PNA-X with New Nonlinear features and
capability New phase calibration standard
NVNA FW
For more details: www.agilent.com/find/nvna
Power Amplifier Case Study for Webinar
For this webinar, we take case study of designing a RFMD GaN device based
Power Amplifier design with following specifications:
Parameters Specifications
Centre Frequency 1 GHz
Bandwidth +/- 50 MHz
Output Power (PEP) 25 Watts
Gain > 10 dB
Input/Return Loss < -10 dB
PAE >40%
3rd Order IMD < -35 dBc
*PEP: Peak Envelope Power
Reference: http://vk1od.net/measurement/RfPowerTerms/PEP.htm
Step1: Amplifier DC IV characteristics 1st step for amplifier design is to perform a DC IV characteristics so that we can observe the IV
characteristics of the non-linear device and decide DC operating condition
ADS provides various built-in templates for simulations like IV characteristics and it can be
inserted on schematic page and can be modified as per device operating range
Step1: Amplifier DC IV characteristics results
Step1a: Amplifier DC Bias Network Once the DC simulation is performed we can design the I/P and O/P bias network either as per the
guideline provided in the device datasheet or using the recommendation from device vendor…
While making bias network it would be advisable to keep width of transistor device so that i/p & o/p
transitions can be taken into account from the very beginning…
Hint: Use of Microstrip Taper is typically
preferred to avoid heavy impedance
discontinuities due to wide widths of
transistor terminals…
Step2: Stability Analysis Once we decide the bias condition and prepare bias network, we can perform Stability Analysis…
Necessary and Sufficient condition of Stability: Stability Factor>1 and Stability Measure>0
Step2: Stability Analysis
As can be seen here, Stability Factor (Blue curve) is greater than 1 and Stability Measure
(Red curve) is greater than 0 over entire frequency band with the help of Stability resistor
in series to Gate hence our device is unconditionally stable and we can begin our amplifier
design….
Note: PA designers have choice to stabilize the device over entire freq range or to stabilize the device
in the operating band and perform conditional matching network design..
LoadPull Analysis
What is Load Pull?
Load Pull is a technique whereby Source Power & Impedance is kept
constant and Load Impedance is varied over a certain impedance range and
device characteristics is measured to capture parameters such as Output
Power, Efficiency, IMD, Harmonics etc
Load Pull Techniques
LoadPull Application Cases
LoadPull Designguide in ADS
Best place to start load pull simulation in ADS is by using load pull
designguide which is provided free in all newer versions of ADS packages.
Load Pull designguide offers various easy to use templates to jumpstart
loadpull simulations
Please view our load pull videos: http://www.youtube.com/watch?v=FTK1pEu1Z64
Load Pull Simulation with a parameter sweep
While we can perform load pull simulations to find out at what load impedance
we obtain the required amount of output power and efficiency etc but we
cannot say how much compression device is in?
In order to find out such things or to find how amplifier performance change
with any parameter such as Input Power, Bias Voltage, Temperature etc, we
can use Parameter Sweep based template from load pull designguide which
can provide lot of useful information to PA designers….
Step 4: Impedance Matching Network Design
Once we perform Loadpull and
other related simulation to find out
optimum impedance, we can
perform impedance matching
network design using either Smith
Chart tool or automated
impedance matching utility in ADS
Step 5: PA performance verification & Optimization
Final step in amplifier design process is to combine all the different piece together
and optimize amplifier performance to meet the required specifications
Final PA Optimized Results
Step 6: PA Output with Input Power Sweep
PA Sweep Results
Step 7: 2-Tone Simulation (with IP Power Sweep)
2-Tone Simulation Results
Step 8: Modulated Signal Analysis
Modulated Signal Analysis Results
Performance for 25 Watts O/P
Performance for 50 Watts O/P
VSA (89600B) Output of Power Amp @25W O/P
VSA (89600B) Output of Power Amp @50W O/P
For More Info:
Anurag Bhargava: anurag_bhargava@agilent.com
Mukul Pareek: mukul_pareek@agilent.com
Toll Free: 1800-11-2929
Customer Support Email: tm_india@agilent.com
Agilent Webpage: www.agilent.com
EEsof Webpage: www.eesof.com
Q & A