Preferably, the nonlinear correction is applied using a parallel processing architecture, whereby two or more samples are processed simultaneously, to accommodate the high sample rate of the expanded bandwidth.įigure 2. The nonlinear correction may be applied to the complex baseband signals using any suitable form of digital signal processing, including both real and complex domain (I/Q or polar) processing.
#The signal path class c power amplifier tutorial series#
The DPD techniques to use are based on subset of the Volterra series memory polynomial and generalized memory polynomial.
Attempting to compensate for the fast variation of PA characteristics or short-term memory effects with conventional DPD (based on Taylor series) schemes can degrade the performance or even make the system unstable. The fast variation is, however, typically not taken into consideration. Most adaptive DPD blocks adapt to the slow variation of PA characteristics. In addition to the correction of the PA nonlinearity, memory effect compensation is an important requirement of the DPD algorithm especially when the signal bandwidth increases. These are typically referred to as memory effects. Another challenge of DPD is the dependence of the PA’s transfer characteristics on the signal’s frequency content, defined as changes of the amplitude and phase in distortion components based on past signal values. The DPD is equivalent to a nonlinear circuit with a gain expansion response that is the inverse of the power amplifier gain compression (AM/AM) and a phase rotation that is the negative of the PA phase rotation (AM/PM) as shown in Figure 1.ĭPD must adapt to variations in PA nonlinearity. Block diagram of a DPD system shows how it linearizes the PA. DPD lets cost-efficient nonlinear PAs operate at higher output powers and into their nonlinear regions with minimized distortion, resulting in greater power efficiency.įigure 1. It also discusses some of the DPD challenges to improve the power efficiency in 5G systems.ĭPD operates in the digital baseband domain, offering lower implementation complexity than alternative techniques such as feedforward linearization, which operates in the RF domain. This article describes the DPD concept and its effectiveness at improving PA efficiency. The DPD must adapt to variations in PA nonlinearity with time, temperature, and use of different operating channels. The concept is based on inserting a nonlinear function (the inverse function of the amplifier) between the input signal and the amplifier to produce a linear output. DPD lets cost-efficient nonlinear PAs run in their nonlinear regions with minimized distortions, resulting in higher output power and greater power efficiency.
Considering the large number of wireless base stations deployed worldwide, improved PA efficiency could substantially reduce the electricity and cooling costs incurred by cellular operators.ĭigital pre-distortion (DPD) provides an effective method to linearize PAs. Thus, more than 90% of the DC power gets lost, turned into heat.
To improve EMV, a PA’s operating point needs to be backed off far from its saturation point, leading to very low power efficiency, typically less than 10%. It also causes in-band distortion, resulting in degradation of its error vector magnitude (EVM) performance. This nonlinearity generates spectral regrowth, leading to unwanted radiation and adjacent-channel interference. Unfortunately, they’re inherently nonlinear. Power amplifiers (PAs) are indispensable components in a wireless communication system. Digital predistortion compensates for an amplifier’s nonlinearities, letting it operate in its nonlinear region for maximum power efficiency.
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