Keysight Technologies Increase Power Amplifier Test Throughput

Keysight Technologies Increase Power Amplifier Test Throughput
Keysight Technologies
Increase Power Amplifier Test Throughput
with PXIe Vector Signal Analyzers, Vector
Signal Generator and Vector Transceiver
Application Note
Accelerate power amplifier
test throughput and high
speed harmonic testing to
achieve cost reductions,
while maintaining high test
Power amplifier designs for mobile handsets are becoming more complex, which directly impacts test
demands and the cost of test. Complexity increases with the introduction of new, wider bandwidth
standards and the increased number of radios to each device. At the same time, demand for improved
battery life is driving efficiency improvements, such as digital pre-distortion and envelope tracking.
Business issues, such as pressure to reduce prices of these devices places greater demands on
engineering teams producing power amplifiers.
Engineers who test mobile power amplifiers and front end modules from design through production are
looking for solutions to reduce test cost through maximizing speed and throughput while ensuring that
the devices meet required performance levels.
This application note provides an overview of the key issues in a power amplifier and front end module
test system related to the RF signal analyzer and generator. It then offers a PXI based hardware and
software solution for achieving fast test throughput.
03 | Keysight | Increase Power Amplifier Test Throughput with the PXIe Vector Signal Analyzers and Generator - Application Note
Key issues faced by power amplifier test engineers
This application note addresses test challenges faced by power amplifier engineers
including the need to:
–– Reduce test times by providing fast input power adjustment and fast power
–– Assess modulation performance quickly with high quality and trusted
Figure 1 shows a simplified block diagram for the RF vector signal analyzer and signal
generator in a typical power amplifier/front end module test system. Typical power
amplifier modules require an input power level of 0 to + 5 dBm, digitally modulated
according to communication standards such as WCDMA or LTE. The specified
performance of the power amplifier or front end module is normally set at a specific
output level of the DUT. If the devices have small variations in gain, it may be necessary
to adjust the power level from the PXI VSG to get the correct output level of the DUT.
Only after the DUT output level is set at the correct value, can the specified parameters
be tested. The time spent adjusting the PXI VSG to get the correct DUT output power
can be a major contributor to the test time and the overall cost of test.
The PXI VSG is connected to the DUT using a cable and switches. The switching may be
used to support testing of multi-band modules or multi-site testing. The combination
of the RF cables and the switching network can add several dB of loss between the
output of the PXI VSG and the input of the DUT, which requires higher output levels from
the PXI VSG. Since the tests are performed with a modulated signal, the PXI VSG must
also have adequate modulation performance at the higher power levels.
The PXI VSA is also connected to the DUT using switches and cables. If the PXI VSA is
not able to make fast and accurate power measurements, a power meter may also be
required on the DUT output. The signal analyzer needs to perform measurements of
power, ACPR, EVM, harmonics and other parameters. It needs to measure all of these
parameters quickly and accurately and be able to switch between measurement modes
in minimal time.
Figure 1. Typical Power Amplifier/Front End Module Test Setup
RF Out
RF Out
Signal Generator
RF Out
Signal Analyzer
04 | Keysight | Increase Power Amplifier Test Throughput with the PXIe Vector Signal Analyzers and Generator - Application Note
Using the PXI VSAs and VSG to increase test throughput and quality
The Keysight Technologies, Inc. M9391A and M9393A PXI VSAs and M9381A PXI VSG
offer unique features that:
–– Increase test throughput with fast amplitude and frequency switching as well as
hardware accelerated power measurements.
–– Enable synchronization with an arbitrary waveform generatorfor envelope generation
to support test of envelope tracking devices.
–– Provide good modulation performance, particularly at highpower 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
–– Further reduces test development time through code reuse.
The M9381A PXI VSG reduces the overall switching time through a powerful, innovative
tuning methodology. It further increases throughput by providing good linearity and
repeatability which reduces the number of iterations required to get the DUT to the
correct power output level. The PXI VSG also offers high modulation quality so you can
drive amplifiers directly without having to add external amplification.
Several other vector signal generations offer amplitude and frequency switching times
of less than 1 ms when used in list modes. However, since the output level of the signal
generator cannot be predetermined for each test, list modes cannot be used for power
amplifier testing. Other signal generators require significantly longer switching time
when controlled through anormal programming interface. The PXI VSG offers the fastest
switching time on the market of 250 μs from its programming interface and 10 μs in list
mode, with fastune, an exclusive baseband tuning technology innovation.
The PXI VSG comes with 40 MHz bandwidth, but can be upgraded to 100 MHz or 160
MHz. The baseband frequency offset can be programmed to any offset within the
purchased modulation bandwidth. For example, the 160 MHz bandwidth option allows
the baseband frequency offset to be set to ±80 MHz. The baseband power offset can
be set to 20 dB below the programmed RF power level and still achieves high quality
modulation performance. To take advantage of this feature for power amplifier testing,
engineers can set the RF frequency to the center of the band being tested and the RF
power level to the maximum required for all tests. From there, baseband frequency
adjustments are made to test at multiple frequencies across the band and the baseband
power level is adjusted to servo the DUT output level to the correct value.
Better linearity, repeatability and resolution offered by the PXI VSG further reduces the
test time by enabling the servo loop to converge in fewer steps. After the DUT output
level is measured by the signal analyzer, the new value of the PXI VSG output power is
calculated based on the difference between the measured power and the desired power.
Then, the PXI VSG is adjusted by the amount necessary to achieve the correct DUT
output power.
05 | Keysight | Increase Power Amplifier Test Throughput with the PXIe Vector Signal Analyzers and Generator - Application Note
The PXI VSG provides high modulation quality, particularly at high output power levels.
In many cases, signal levels as high as + 15 dBm may be needed to overcome the loss
between the PXI VSG and the DUT input. As shown in Figure 2, the PXI VSG has excellent
adjacent channel power (ACPR) at high output power levels. At + 10 dBm, there is little
or no degrading of the ACPR and at + 15 dBm, the ACPR level is still near 60 dBc.
The M9391A PXI VSA reduces the overall test time through a hardware accelerated
power measurement methodology. Power measurements are accumulated in real time in
the digitizer, requiring only a single value to be returned to the application program and
no computation of power from the IQ data in the controlling PC. In addition, the PXI VSA
provides very repeatable power measurements, with acquisition times as low as 10 μs.
Figure 3 shows the repeatability of the PXI VSA’s power measurements with acquisition
times from 10 μs to 1 ms at power levels from the expected input level to 75 dB below
the expected input level. For power levels as low as 25 dB below expected input level,
the PXI VSA can provide a power measurement with 0.005 dB standard deviation in a
total execution time of less than 400 μs. When combined with the power level switching
speed of the PXI VSG, the step time for a power servo loop can be less than 1 ms.
Power servo and ACPR measurements can be made using the hardware accelerated
power measurement technique mentioned in the preceding paragraph or by using
hardware accelerated FFT acquisition mode. The FFT acquisition mode offers similar
accuracy and repeatability, but enables ACPR to be calculated from a single acquisition
that spans all of the desired adjacent channels. By re-using the last acquisition from the
power servo loop, the ACPR values can be calculated with no additional measurement
Emerging power efficiency technologies, such as envelope tracking, and digital predistortion can be supported through a configuration of PXI hardware with Signal Studio
software for power amplifier test. For more information, please see the application note:
Reduce Power Amplifier ET and DPD Test Times with PXIe Measurement Accelerator and
Reference Solution, literature no. 5992-0883EN.
ACPR (dBc)
Other PXI Source 10 MHz Offset
Other PXI Source 5 MHz Offset
M9381A 10 MHz Offset
M9381A 5 MHz Offset
Output Power (dBm)
Figure 2. Note the M9381A shows little ACPR degradation below 10 dBm and is better than 60 dBc at 15 dBm.
06 | Keysight | Increase Power Amplifier Test Throughput with the PXIe Vector Signal Analyzers and Generator - Application Note
Repeatability vs. acquisition time vs. power level
Power Level Relative to the Expected Input
10 μs
100 μs
1 ms
0 dB
-25 dB
-75 dB
Std Dev
Std Dev
Std Dev
Figure 3. Repeatability of power measurements using the M9391A.
Using the PXIe vector transceiver to speed test time
for manufacturing
To minimize manufacturing test system development and measurement time, a calibrated
PXIe vector transceiver instrument module extends the capability of the RF PA/FEM
reference solution to the production floor. The vector transceiver combines vector signal
generation and analysis in one 4-slot unit and aims to more than double manufacturing
test throughput, while minimizing the use of valuable floor space.
Keysight’s M9420A PXIe vector transceiver (VXT) is purpose-built for rapid solution
creation and faster throughput in manufacturing test of wireless components and IoT
devices. Up to four VXT’s can be configured in a single 18-slots PXI chassis. Alternatively,
a versatile single-chassis solution with one VXT, one DIO card and one of Keysight’s
award-winning single-slot PXI VNAs can be used for S-parameter measurements. The
PXIe VXT provides frequency coverage from 60 MHz to 6 GHz and up to 160 MHz I/Q
bandwidth. With a maximum of +18 dBm output power, the VXT compensates for signal
losses through switch matrices.
The built-in servo routine accurately determines the final PA output power to control PA
distortion. Traditional methods for power measurements have involved either swept or
I/Q acquisitions followed by software processing. Though the software processing speed
can scale with the capability of the processor, FPGA-based measurements have recently
been utilized to further increase measurement speed. The PXIe VXT features real-time
FFTs that enable high-speed measurements of signal power and adjacent-channel power
ratio (ACPR), which can compress the power servo test time from 70 to 110 ms to a
handful of milliseconds as shown in the table below.
Swept Acquisition and Fast I/Q Acquisition,
Software Processing
Mixed Hardware and
Software Processing
FPGA Accelerated
with VXT
Power Servo WCDMA
70 ms
20 ms
5.5 ms
Power Servo FDD LTE
110 ms
20 ms
5.5 ms
Figure 4. Power servo time comparison among traditional swept acquisition, fast I/Q acquisition and FPGA accelerated processing together with PXIe VXT hardware.
Manufacturing system developers can easily create test solutions for power amplifiers
(PA) and front-end modules (FEM) using the VXT’s built-in software and FPGA-accelerated measurements. To reduce programming time, proven open-source example software
routines are included with PA reference solution.
07 | Keysight | Increase Power Amplifier Test Throughput with the PXIe Vector Signal Analyzers and Generator - Application Note
Harmonic Measurements
Harmonics measurements are part of the typical characterization test bench because all RF
PA amplifiers exhibit harmonic distortion to some extent. Generally, a spectrum analyzer that
can perform measurements with a low noise floor, minimal images, and high dynamic range
is used to determine harmonic content and spurs. Since cellular and wireless connectivity
applications cover up to 6 GHz, the required frequency range of the test bench’s spectrum
analyzer should be at least 18 GHz in order to measure the 3rd harmonic. For characterization
or manufacturing, one of the main challenges is to combine these requirements with highspeed test.
Traditional spectrum analyzer designs use YIG oscillators which provide tuning sweeps
generally taking tens of milliseconds, which may not be fast enough for today’s throughput
requirements. The M9393A PXIe performance vector signal analyzer is designed with Voltage
Controlled Oscillators (VCO) instead of YIGs, combined with a stepped FFT technique. It
eliminates band switching penalties and dramatically improves harmonics measurement
speed. With the fast tuning LO, 160 MHz analysis bandwidth, and high speed back-end
processing, the M9393A allows extremely fast “sweeps,” across the entire 27 GHz frequency
range, in a fraction of a second.
Because not all RF PA characterization and production test systems require harmonic test
capabilities, it is important to ensure that the various PXI VSAs share common architecture
to maximize test code leverage and to reduce test development time. Using the same high
speed signal processing and measurement software across Agilent’s line of PXIe VSAs offers
consistency in measurements and programming in frequency ranges from 3 GHz to 27 GHz.
The M9393A and M9391A PXIe VSAs share similar programming models and can be used with
the same X-Series measurements applications without the need to purchase new software
Application Software
The PXI VSAs, VSG and VXT can be used with the same measurement applications that
run on corresponding Keysight bench top instruments. Use Signal Studio software for
simplifying the creation of specific test signals and X-Series measurement applications
for easily trouble-shooting test setups using displays and one-button measurements. For
complex signal analysis, industry-leading 89600 VSA software can be used for standardsspecific demodulation analysis and advanced displays. Benefit from excellent correlation of
measurement results at multiple points in your product design cycle when using Keysight
software with benchtop and modular instruments, as well as the common programming
interface, enabling code reuse and reduced test development time.
08 | Keysight | Increase Power Amplifier Test Throughput with the PXIe Vector Signal Analyzers and Generator - Application Note
Ordering Information
Main Hardware Components
Recommended configuration for production test
Frequency range 60 MHz to 6 GHz
RF modulation bandwidth 160 MHz
Memory 512 MSa
High output power
PXIe frequency reference
PXIe Vector Signal Generator
1 MHz to 6 GHz
M9301A PXIe Synthesizer
M9310A PXIe Source Output
M9311A PXIe Digital Vector Modulator
PXIe Vector Signal Analyzer
1 MHz to 6 GHz
M9301A PXIe Synthesizer
M9350A PXIe Downconverter
M9214A PXIe IF Digitizer
PXIe Performance Vector Signal Analyzer
9 kHz to 27 GHz
M9308A PXIe Synthesizer
M9365A PXIe Downconverter
M9214A PXIe IF Digitizer
PXIe Vector Transceiver
60 MHz to 6 GHz
Vector generator
Vector analyzer
PXIe Frequency Reference
10 MHz to 100 MHz
PXIe Measurement Accelerator with digital predistortion and envelope tracking gateware
Frequency range: 1 MHz to 6 MHz
RF modulation bandwidth: 100 MHz
Memory: 32 MSa
Fast switching
Frequency range: 1 MHz to 6 GHz
Analysis bandwidth: 100 MHz
Memory 128 MSa
Fast switching
PXIe frequency reference
Harmonic test configuration includes
Software Information
Supported operating
Standard compliant drivers
Microsoft Windows 7 (32/64-bit)
Supported application
development environments
Keysight IO Libraries
(version 17.0 or newer)
VisualStudio (VB.NET, C#, C/C++), VEE,
Includes: VISA Libraries, Keysight Connection Expert, IO Monitor
Related Literature
PXIe Digital Stimulus/Response with PMU
Recommended configuration for design validation test
For more options on these configurations, or for recommended
configurations for envelope tracking and/or digital pre-distortion
test, please refer to the RF PA/FEM Reference Solution configuration guide, literature number 5992-0072EN.
Frequency range: 1 MHz to 6 MHz
RF modulation bandwidth: 100 MHz
Memory: 512 MSa
High output power
Fast switching
Frequency range: 9 kHz to 18 GHz
Analysis bandwidth: 100 MHz
Memory 512 MSa
Fast switching
PXIe frequency reference
Configuration Guide
Application Note
RF PA/FEM Characterization and Test
Reference Solution
(literature no. 5992-0071EN)
RF PA/FEM Characterization and Test
Reference Solution
(literature no. 5992-0072EN)
Reduce Power Amplifier DPD/ET Test
Times with PXIe Measurement Accelerator
and Reference Solution
(literature no. 5992-0883EN)
9 | Keysight | Increase Power Amplifier Test Throughput with the PXIe Vector Signal Analyzers and Generator - Application Note
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Published in USA, September 27, 2015
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