Challenges for Power Amplifier Testing with Envelope Tracking

transcript

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

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

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

DC supply

BasebandUp -

converterI/Q RF

Constant supply voltageEnergy

dissipated

as heat

RF signal

Conventional approach

ı With a constant supply voltage, high amount of

energy is dissipated as heat

PINPOUT

DC supply

BasebandUp -

converterI/Q RF

RF signal

DC modulator

Envelope tracking

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

Envelope

detector

Envelope Tracking – Test Challenges

DC supply

BasebandUp -

converterI/Q RF

Envelope

detectorShaping

adjustmentDC modulator

Signal Generator

Envelope

analysis

Signal Analyzer

DC supply

BasebandUp -

converterI/Q RF

Envelope

detectorShaping

Signal Generator

Synchronization

ı Synchronization between RF signal and modulated supply voltage VCC

analysisRF

Envelope

Signal Analyzer

DC supply

BasebandUp -

converterI/Q RF

Envelope

detectorShaping

Signal Generator

analysisRF

Envelope

Signal Analyzer

ı Apply shaping curve

DC supply

BasebandUp -

converterI/Q RF

Envelope

detectorShaping

Voltage

Signal Generator

𝐏𝐀𝐄 in percentage =RF Power out − RF Power in

DC Power%

analysis

DC power

analysis

Envelope

Signal Analyzer

ı Instantaneous power added efficiency (PAE) calculation

Current

DC supply

BasebandUp -

converterI/Q RF

Envelope

detectorShaping

Signal Generator

RF and

distortion

analysis

DC power

analysis

Envelope

Signal Analyzer

ı Optional: distortion analysis

DC supply

Baseband

distortion

converterI/Q RF

Envelope

detectorShaping

Signal Generator

ı Optional: distortion analysis

ı Optional: predistortion

RF and

distortion

analysisRF

Envelope

Signal Analyzer

DC power

analysis

Envelope Tracking – Measurement Setup

DC modulator

Signal Generator Signal Analyzer

R&S®SMW200AR&S®FSW

Generate RF and

envelope signalRF and

Voltage/current

analysis

Envelope

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

ı Preset configuration for envelope signal

ı Specific DC modulator parameters

like Gain, V CC Offset or Impedance are taken into account

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

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

Inv. Env.

Shaping setting Resulting Envelope

Signal Analysis

R&S FSW

Signal- and Spectrum-Analyzer FSW-K18 (Amplifier Measurements)

FSW-K18 PAE measurement (1)

PAE calculation:

DC modulator

Signal Generator Signal Analyzer

R&S®SMW200AR&S®FSW

Generates RF and

envelope signalRF and

Voltage/current

analysis

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:

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

FSW-K18 Digital Predistortion

Measure

AM/AM AM/PM

with FSW-K18

Generate

DPD Tables

Transfer

Tables to

SMW-K541

Activate DPD

SMW-K541

Activate DPD

SMW-K541

Generate DPD

Tables

(automatically)

Transfer Tables

from FSW-K18

to SMW-K541

Maximum Output

Power of the PA

FSW-K18

SMW-K541

Automatic Transfer

and configuration via

FSW-K18 Digital Predistortion

Interface to SMW-K541

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)

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-

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

Thank you

for your attention!

Challenges for Power Amplifier Testing with Envelope Tracking

Technology