challenges for power amplifier testing with envelope tracking
DESCRIPTION
September 25th, 2014 Rainer Lenz, Product Manager Signal Generators, R&STRANSCRIPT
Challenges for Power Amplifier
Testing with Envelope Tracking -
concepts, pit falls, state of the
art and trends
Cambridge Wireless Workshop
Advance Techniques for Radio Transmitters
September 25th, 2014
Rainer Lenz
Product Manager Signal Generators
2Improving the Efficiency of Your Envelope Tracking Test Setup
Agenda
ı Envelope Tracking – Overview
ı Envelope Tracking - Test Challenges
ı Measurement Setup
ı Summary
3Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Overview
Low battery. Connect charger.
ı Beside display and processor, a main contributor to the power consumption of a
modern smartphone is the TX power amplifier (PA)
ı Envelope tracking is a technique to improve the efficiency of PAs, thus
increasing battery lifetime
4Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Overview
ı Modern communication standards, such as LTE, show a high peak-to-average
ratio (PAR), i.e. up to 7 dB for LTE uplink signals
ı PAs are most efficient when operating near its maximum output power
ı For signals with high crest factor, PAs operate in low efficiency regions most of
the time
typical power added efficiency (PAE)
signal amplitude probability
5Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Overview
DC supply
BasebandUp -
converterI/Q RF
Constant supply voltageEnergy
dissipated
as heat
RF signal
Conventional approach
PA
ı With a constant supply voltage, high amount of
energy is dissipated as heat
PINPOUT
6Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Overview
DC supply
BasebandUp -
converterI/Q RF
RF signal
DC modulator
Envelope tracking
PA
Modulated supply voltage
Envelope
ı Envelope is calculated from the baseband
signal with (𝐼2 + 𝑄2)
ı DC supply voltage is modulated according to
the envelope of the RF signal
ı As a result the PA is operated in high efficient
regions most of the time
PIN
VCC
POUT
Envelope
detector
7Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Test Challenges
DC supply
BasebandUp -
converterI/Q RF
Envelope
detectorShaping
Delay
adjustmentDC modulator
PAPIN
VCC
POUT
Signal Generator
Envelope
RF
analysis
Signal Analyzer
8Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Test Challenges
DC supply
BasebandUp -
converterI/Q RF
Envelope
detectorShaping
Delay
adjustmentDC modulator
PAPIN
VCC
POUT
Signal Generator
Synchronization
ı Synchronization between RF signal and modulated supply voltage VCC
RF
analysisRF
Envelope
Signal Analyzer
9Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Test Challenges
DC supply
BasebandUp -
converterI/Q RF
Envelope
detectorShaping
Delay
adjustmentDC modulator
PAPIN
VCC
POUT
Signal Generator
RF
analysisRF
Envelope
Signal Analyzer
ı Synchronization between RF signal and modulated supply voltage VCC
ı Apply shaping curve
10Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Test Challenges
DC supply
BasebandUp -
converterI/Q RF
Envelope
detectorShaping
Delay
adjustmentDC modulator
PAPIN
Voltage
POUT
Signal Generator
𝐏𝐀𝐄 in percentage =RF Power out − RF Power in
DC Power%
RF
analysis
DC power
analysis
RF
Envelope
Signal Analyzer
ı Synchronization between RF signal and modulated supply voltage VCC
ı Apply shaping curve
ı Instantaneous power added efficiency (PAE) calculation
Current
11Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Test Challenges
DC supply
BasebandUp -
converterI/Q RF
Envelope
detectorShaping
Delay
adjustmentDC modulator
PA
Signal Generator
PIN
VCC
POUT
RF and
distortion
analysis
DC power
analysis
RF
Envelope
Signal Analyzer
ı Synchronization between RF signal and modulated supply voltage VCC
ı Apply shaping curve
ı Instantaneous power added efficiency (PAE) calculation
ı Optional: distortion analysis
12Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Test Challenges
DC supply
Baseband
and
pre-
distortion
Up -
converterI/Q RF
Envelope
detectorShaping
Delay
adjustmentDC modulator
PA
Signal Generator
ı Synchronization between RF signal and modulated supply voltage VCC
ı Apply shaping curve
ı Instantaneous power added efficiency (PAE) calculation
ı Optional: distortion analysis
ı Optional: predistortion
PIN
VCC
POUT
RF and
distortion
analysisRF
Envelope
Signal Analyzer
DC power
analysis
13Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking – Measurement Setup
DC modulator
PIN
VCC
POUT
Signal Generator Signal Analyzer
R&S®SMW200AR&S®FSW
LAN
Generate RF and
envelope signalRF and
Voltage/current
analysis
PA
DUT
RF
Envelope
14
Signal GenerationAvailable Options
R&S SMW200A
Vector Signal Generator
R&S SMW-K540
R&S SMW-K541
Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Tracking - User Interface
15
eTrak
ı Preset configuration for envelope signal
ı Specific DC modulator parameters
like Gain, V CC Offset or Impedance are taken into account
Improving the Efficiency of Your Envelope Tracking Test Setup
Envelope Settings - Synchronization
ı Envelope to RF synchronization below 1 ns is required
ı Can be adjusted in SMW with ps resolution in real time
RF Envelope
16Improving the Efficiency of Your Envelope Tracking Test Setup
Different shaping modes
ı Table (Look-Up Table with up to 4000 comma separated value pairs)
ı Polynomial (up to 10 polynomial coefficients)
ı Detroughing (3 different functions)
Real time Shaping capabilities
Envelope
RF
Inv. Env.
Shaping setting Resulting Envelope
17Improving the Efficiency of Your Envelope Tracking Test Setup
18
Signal Analysis
R&S FSW
Signal- and Spectrum-Analyzer FSW-K18 (Amplifier Measurements)
Improving the Efficiency of Your Envelope Tracking Test Setup
FSW-K18 PAE measurement (1)
PAE calculation:
DC modulator
PIN
VCC
POUT
Signal Generator Signal Analyzer
R&S®SMW200AR&S®FSW
LAN
Generates RF and
envelope signalRF and
Voltage/current
analysis
PA
DUT
RF
Envelope
ı RF power in -> from SMW
ı RF power out -> measured at RF port from FSW
ı DC power in -> measured at Baseband ports
(2 ports for 2 independent voltages)
DC Power
PAE calculation requires synchronous information of:
Improving the Efficiency of Your Envelope Tracking Test Setup
FSW-K18 PAE measurement (2)
ı Oscilloscope probes for easy connection
ı Usage of shunt resistor for supply current
measurement
RF Output
(to FSW)
RF Input
(from SMW)
ı PAE graphical display
Improving the Efficiency of Your Envelope Tracking Test Setup
FSW-K18 Digital Predistortion
21
Measure
AM/AM AM/PM
with FSW-K18
Generate
DPD Tables
Transfer
Tables to
SMW-K541
Activate DPD
on
SMW-K541
Activate DPD
in
SMW-K541
Generate DPD
Tables
(automatically)
Transfer Tables
from FSW-K18
to SMW-K541
Maximum Output
Power of the PA
Improving the Efficiency of Your Envelope Tracking Test Setup
22
FSW-K18
SMW-K541
Automatic Transfer
and configuration via
LAN
FSW-K18 Digital Predistortion
Interface to SMW-K541
Improving the Efficiency of Your Envelope Tracking Test Setup
23Improving the Efficiency of Your Envelope Tracking Test Setup
SMW Digital Predistortion implementation
ı DPD applies amplitude and phase offset on every IQ sample in real time
ı DPD alters the signal statistics and the signal level
ı PEP, Level and Crest Factor before and after DPD are shown
ı Adjustable mean Level Reference Mode (Before or After DPD)
24
Envelope Tracking – Summary and Status
R&S®SMW200A
SMW-K540 Envelope tracking Available
SMW-K541 Digital
Predistortion
Available
R&S®FSW
FSW-B71 Synchronous analog
baseband inputs
Available
i.e. RT-
ZP10
Oscilloscope probe
connection to FSW
Available
FSW-K18 Amplifier Measurements Available
ı RF and envelope signals out of
one box
ı Realtime shaping and delay
adjustment
ı Power sweeps with automatic
recalculation of the envelope signal
ı Realtime Digital predistortion
ı RF and envelope signal analysis
in one box
ı Fastest measurement speed for
EVM/ACLR, Distortion Analysis
and PAE calculation
ı Highest dynamic range,
simplifying the test setup
Improving the Efficiency of Your Envelope Tracking Test Setup
Thank you
for your attention!
Improving the Efficiency of Your Envelope Tracking Test Setup