Visual System Simulator™

Visual System
Simulator
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line
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White Paper
Here, LabVIEW’s benefits become clear as the design flow moves
toward actual hardware, as the VI can be made more realistic by
adding corrective algorithms and extending this VI to measure the
attenuators, phase shifters, and other components that would
otherwise only be modeled in the VSS system diagram.
One of the benefits of the synergy between VSS and LabVIEW is
in the ability of VSS to capture the simulated 1900 MHz amplifier
and LabVIEW to capture the actual attenuators and phase shifters.
The user can determine when and how to switch from manual to
algorithmic behavior given the challenges and progress of the design
flow. The LabVIEW VI is added to the VSS system diagram to create
the predistorted signal (Figure 9). The VSS input signal is transferred
through the LabVIEW block to the VI and separated into phase and
magnitude. These signals are then used early in the development of
the predistortion circuit to drive a look-up table or simple continuous
algorithm corresponding to the phase and magnitude of the output
signal. Operating on the complex signal (as phase and magnitude)
allows direct implementation of the phase shifter and attenuator. As
the digital phase shifter and attenuator are digitally controlled, the
look-up table can be implemented in an FPGA for easy recalibration
or updating as determined by system performance.
First-pass predistorter results are shown in Figure 10. The blue
trace shows the signal as it would appear without predistortion,
while the red trace shows an early manual correction using the
LabVIEW VI to alter the phase and magnitude as a predistortion
function. The improvement is seen in the spectral mask, where
regrowth is reduced by about 25 dB. As the amplifier is driven
harder, the performance should be even more pronounced thereby
maintaining the linearity of the amplifier at higher power levels.
SUMMARY
Achieving the highest possible performance from circuits used
in third-and fourth-generation wireless systems requires the
seamless integration of simulation and measurement at every
stage of the design process. Designers who deviate from this are
at risk as the further in the design process that serious design
issues are discovered, the more time (and money) it will take to
remedy them. AWR’s VSS software and National Instruments’
LabVIEW signifi cantly reduce the possibility that the latter scenario
will occur, as the circuit and its components are passed back
and forth seamlessly between the two tools. The result is better
performance, shorter design time, and a minimum of frustration.
Figure 9: A LabVIEW VI added to the VSS system diagram to create
the predistorted signal.
Figure 10: First-pass predistorter results. The blue trace shows the
signal as it would appear without predistortion, while the red
trace shows an early manual correction using the LabVIEW
VI to alter the phase and magnitude as a predistortion
function. The improvement is seen in the spectral mask,
where regrowth is reduced by about 25 dB.
View the AWR
VSS/LabVIEW
Integration video
on AWR.TV.
AWR, 1960 East Grand Avenue, Suite 430, El Segundo, CA 90245, USA
Tel: +1 (310) 726-3000 Fax: +1 (310) 726-3005 www.awrcorp.com
Copyright © 2012 AWR Corp. All rights reserved. AWR is a National Instruments Company. AWR, and the
AWR logo are registered trademarks and Visual System Simulator is a trademark of AWR Corporation.
All others are trademarks of their respective holders.
WP-VSS-NI-2012.5.31