Testing RFIC Power Amplifiers with Envelope...

Testing RFIC Power Amplifiers with Envelope Tracking

April 2014

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Agenda

New emerging technologies such as envelope tracking and DPD and their implications

Addressing Test Challenges

Key Test Challenges

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Agilent’s PA Reference Solution

Power Amplifier Key Test Challenges

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• Must now test 9 bands and 5 modes

Device complexity continues to increase

Amount of testing is increasing while price continues to be driven down

• Envelope tracking & Digital Pre-distortion

New techniques add additional test challenges

Need for Speed

Typical Power Amplifier (PA) Speed challenge: Adjustment routine can be a significant percentage of overall test time

RF OutSignal Generator

RF OutRF In

RF OutRF InSwitching

RF InSignal Analyzer

Switching

DUT

• DUT specifications are at a specific output power level• VSG level must be iteratively adjusted to achieve the correct DUT output power

How do you improve measurement speed?

Power Measurements: Real time signal processing to reduce power measurement time to slightly more than the signal acquisition timeChanging VSG Power Level: Faster amplitude switching times and better linearity reduces the time to change the level and the number of required iterations by switching to the correct power level

Fast ACPR and EVM measurement challenges

• Large number of ACPR measurements due to increased modes and bands

• Need for speed has caused a shift away from traditional measurement hardware, which also changes measurement algorithms, sometimes leading to erroneous results

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Harmonics Measurements Challenge

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Agilent Technologies

• Provide good phase noise, but are slow for tuning

Traditional spectrum analyzer designs use YIG oscillators

• Many 6 GHz analyzers have been optimized for speed, but many of these advantages are lost with higher frequency analyzers

The 2.7 GHz LTE band requires greater than a 6 GHz analyzer to measure the third harmonic

• Typical tuning time is in the order of 20 ms

Tuning time across bands is significantly longer, adding measureable time to harmonics measurements

Agenda



Key Test Challenges

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Data Acquisition Modes for Fast Signal Processingwith the M9391A Vector Signal AnalyzerTwo Data Acquisition Modes are of most interest for Power Measurements

Power Mode:• Configurable Bandwidth, Acquisition Time and

Channel Filter• Single Value for Integrated Power Measurement

from IQ time record averaged in FPGA

FFT Mode• Data Output in Frequency Domain via Hardware

FFT with 64 to 512 bins including averaging and windowing

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Baseband Frequency and Amplitude Offsetwith the M9381A Vector Signal Generator• Signal Processing ASIC in baseband generator supports

changing Frequency and Amplitude of RF Signal without Adjusting Analog Hardware (fastune technology innovation)

• Power Servo Loop Approach:• Set the “RF Power Level” to the maximum level that may

be required from the source• Use the “baseband power level” to adjust the power level to

the required input level• Up to 20 dB amplitude changes in 200 µs using

command interface

160 MHz

20 dB

< 200 us

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Input Power Servo / ACPR Measurement Procedure FFT Acquisition For Fast Servo and ACPR

Setup VSG Output level

Target output power/ Expected

Gain

Use VSA FFT Acquisition to Measure and

Calculate DUT Output Power

Is Output within

Tolerance?

Adjust VSG Baseband Power Offset based on measurement

Can we adjust the

VSG baseband

power?

No

No

Yes

Set Baseband Power Offset to 0 for maximum Pout of DUT,

Count set to -1

Calculate Pin and Gain from VSG Output

Yes

Use Last FFT from Power Servo to

Calculate all Channels for ACPR Measurement.

ACPR in 0 ms!

Trusted and Correlated EVM Measurements

• M9381A provides good modulation performance, particularly at high power levels and very linear power level changes.

• Achieve continuity of measurement results from R&D to manufacturing, as well as from previous generation test systems by using X-Series measurement applications

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Harmonics Measurement Speed Improvements

Fast tuning LO with VCOs instead of YIG• Stepped vs Swept • No band switching penalties• Give up a little phase noise performance but gain speed

Correlation between 6 GHz & 27 GHz analyzers• Common high speed signal processing• Common X-series measurement applications

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Agilent Technologies

Agenda



Key Test Challenges

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• Improve battery life• Increase RF amplifier performance over broad frequencies • Lower distortion• Reduce heat dissipation

Envelope Tracking - The How & Why

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Envelope and RF Signal Timing Alignment

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Timing alignment of the envelope and RF signal is critical for best performance

Typical alignment needs to be within 1 ns for a 20 MHz LTE signal to avoid an asymmetric ACLR

Envelope Tracking Production Test Techniques

Test Requirements are still evolving!

Possible Scenarios:

• System Functional Test: • Add ETPS and AWG to Test System• Test Same Parameters as before, maybe with different limits• Minimal Impact on Test Time

• Parametric Test:• May add ETPS and AWG to System• Basic Measurements such as Gain Compression, AM/AM,

AM/PM Conversion and PAE• Moderate Impact on Test Time

• Enhanced Functional Test:• Add ETPS and AWG to Test System• New Tests such as ACPR vs. Timing or PAE vs. Time• This has the largest Impact on Test Time

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ET Benefits• Improved ACPR• Improved PAE• Lower Operating

Temperature

Digital Pre-Distortion (DPD): The How & WhyModern communication systems• Signals have high peak-to-average

power ratios (PAPR).• Must operate with high power-added

efficiency (PAE).

High PAPR is a consequence of high spectral efficiency• Multiple-Carrier Signals (MC GSM, MC

WCDMA)• CDMA (WCDMA, CDMA2000)• OFDM (LTE, WiMAX)

High PAE is achieved when the RF power amplifier (PA) is driven towards saturation

Operation near saturation inherently results in higher signal distortion

Maximum correctablepower

Psat

INPUT POWER

OUTPUTPOWER

LINEAR REGION

DPDREGION

LINEARIZEDDPD + PA

PA, WITH GAINCOMPRESSION

DPD GAINEXPANSION

+ =

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DPD corrects PA nonlinearities resulting in higher performing power amplifiers

Agenda



Key Test Challenges

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RF Power Amplifier Test, Reference SolutionManufacturing / DVT

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M9381A PXIeVector Signal Generator

M9391A PXIeVector Signal Analyzer

M9018A PXIe Chassis

M9036A Embedded Controller

N6700B with N6782A (1 to 4)4 channel SMU

RF OutRF In

ETPS

Vcc VbatV..V..

33522B Arbitrary WaveformGenerator

Envelope

N76XX Signal StudioWaveform Creation

Envelope Generation

M90XXModular X-Series Measurement Applications

GUI examples & Test Libraries

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Proprietary Control

RFFE

2

RF signal with DPD

X-Series Applications for Modular Products –Cellular Communication

LTE FDD

LTE TDD

W-CDMA/HSPA/HSPA+

TD-SCDMA/HSPA

cdma2000/cdmaOne

1xEV-DO

Common algorithms, programming commands and shared library of measurement applications across X-Series signal analyzers and M9391A PXI VSA ensure consistent, repeatable results

www.agilent.com/find/xseriesapplications

GSM/EDGE/EDGE Evo

Evaluation Software environment

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AgModularVsa IVI-COM DriverM938xA IVI-COM Driver

Test Program:Test_WCDMA Test_LTE5MHz Test_LTE_10MHzTest_GSM Test_EVDO Test_WLAN

Power Amp Test Library:Init_Instruments setupVsgVsa measPoutClose_Instruments setupVsgVsaFixedPin measStdAcprLoad Waveforms servoInputPower measLteAcpr

measSpecHarms

RF PA Test Evaluation GUI

89600 VSA & X-SeroesMeasurementApplications

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RF PA Test Evaluation GUIC# Form Application

Accelerates Evaluation

Uses IVI-COM Driver for VSA/VSG

Uses SCPI for X-Apps, AWG and Power Meter

Power Servo, EVM, ACPR, SEM and Harmonics Measurements

Control for ET ARB, RFFE Module and DC SMUs

Data Logging + Test Times

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LTE Envelope Tracking SetupEnvelope Tracking uses 33522B AWG to play Envelope Signal Generated from Signal Studio

Evaluation GUI settings • DC Offset and Amplitude • Nominal IQ Delay to Align RF and

Envelope Signals hard coded• Different values for different

sample rate• Offset from nominal Delay

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ACPR vs IQ delay testManual Adjustment of IQ

Delay from M938x SFP

Introducing the RF Power Amplifier Test Reference Solution with Envelope Tracking

Extremely fast modulation analysis, excellent accuracy and repeatability, and source code optimized for speed

Fast EVM measurements < 50 ms, nom

Fast Servo loop convergence < 5 ms, nom

Fast ACPR measurements 0 ms, nom

Highest test throughput, reduced cost, & rapid integration into power

amplifier test environments

Key Features Benefits

Adjustable RF signal/ envelope skew to ± 1 psresolution over ± 250 ns range

Tight synchronizationbetween RF signal and envelope

Real-time signal processing

Fast measurements

Test libraries and source code examples

Easy evaluation and integration

Questions?

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Agilent PA Test Coverage Over Lifecycle

R&D D&V Production

Modelling & simulation • ADS• PNA-X• N6705B • N6705B

Waveform creation • ADS• Signal Studio

• Signal Studio • Signal Studio

Synchronised RF & envelope signal generation

• N8241A • M8190A• 33522B

• Signal Studio• MXG or M9381A• 33522B

• M9381A VSG• 33522B AWG

PA distortion testing • 89600v17• PXA• DSO9000

• MXA, M9391A, or M9393A VSA

• DSO9000

• M9391A or M9393AVSA

Measurement of instantaneous PAE

Assumes customer provides current & voltage signals

• 89600v17• 8990B

• 89600 with DSO9000 or MXA

• M9210A

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Testing RFIC Power Amplifiers with Envelope...

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