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