[Legacy Report] Digital Predistortion to Linearize High Power Amplifiers for Emerging Wireless Systems

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Today’s modern communication systems face conflicting requirements. They must use signals with high peakto-
average power ratios (called PAPR) and operate with high power added efficiency (called PAE). The high
PAPR requirement is due to the use of transmit RF signals with high spectral efficiency. These signals include
multi-carrier WCDMA (show) and OFDM based LTE (show). High PAE is based on RF power amplifiers
operating with high DC to RF conversion efficiency. Unfortunately, operating the PA in its region of high PAE -
produces high signal distortion. So, we have conflicting requirements. High PAE is achieved at high PA drive
levels. High PAPR results in driving the PA into high distortion levels. And without corrections, the PA needs to
be backed off in drive level to reduce distortion to acceptable limits. Thus, reducing the PAE. So, the problems
is: How to handle signals with high PAPR with the PA operating with high PAE while also having low signal
distortion? The problem is further compounded since PA design for high PAE typically relies on techniques that
result in PA nonlinearities with memory. To reduce the distortion when the PA is operated at its high efficiency
operating points, we will rely on two techniques. 1) PA linearization enables us to drive the PA closer to
saturation without significant signal distortion. 2) Signal preconditioning enables us to reduce the signal peaks
without significant signal distortion as well.
The solution approach here will enable the PA to be driven at its higher drive levels concurrently with limiting
the signal PAPR and will give us higher quality throughput for the next generation communication systems.
The solution relies on signal preconditioning using Crest Factor Reduction techniques and corrections for thePA nonlinearitiesusing Digital Pre-Distortion techniques. This presentation gives a high level picture of aDPD technique with some real world results presented..
Dr. Murthy Upmaka has been with Agilent technologies for the past 14 years in various positions in R&D,
sales and marketing. He is currently a Senior Application Specialist for EDA products.
Prior to joining Agilent Technologies, Murthy had a decade of experience in designing various MW components and systems for Defense applications. He has a PhD in Physics and published over 20 papers in international journals including IEEE journals. He is Senior Member of IEEE for the past 16 years.

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