Abstract
This article presents a novel digital predistortion (DPD) approach to compensate for nonlinear dynamic distortions caused by the supply network of capacitive radio frequency digital-to-analog converters (RF-DACs). The developed DPD concept recreates the voltage distortion on the RF-DAC’s supply network and modulates the input signal such that the effects on the output signal of the RF-DAC are canceled. In contrast to conventional DPD approaches such as pruned Volterra series or memory polynomials, the complexity of the proposed concept is reduced to a feasible level, allowing for implementation in integrated circuits. Furthermore, the derived DPD model allows to use linear estimation algorithms for coefficient training. The presented DPD is demonstrated by measurements of two different capacitive RF-DAC designs and compared with conventional DPD approaches. EVM and adjacent channel power ratio (ACPR) can be improved by up to 6 and 7 dB, respectively, outperforming conventional approaches.
Highlights
T HE demand for high data rates, robust transmissions, and power efficiency poses stringent requirements on the design of integrated wireless transceiver systems
The supply network DPD (SNDPD) is validated with two quadrature capacitive radio frequency digital-to-analog converters (RF-DACs) designs: a capacitive RFDAC-based digital power amplifier (PA) (DPA) [21] and a wideband low-noise quadrature capacitive radio frequency (RF)-DAC, similar to [22]
Both measured RF-DACs are based on a quadrature architecture, and the input to the SNDPD is xon[k] = |xI [k]| + |xQ[k]|, whereas memory polynomial (MP) and generalized MP (GMP) use the magnitude |x[k]|
Summary
T HE demand for high data rates, robust transmissions, and power efficiency poses stringent requirements on the design of integrated wireless transceiver systems. The so-called pruned Volterra models, such as the memory polynomial (MP) [9], [10] or the generalized MP (GMP) [11], reduce the complexity of the Volterra series by sacrificing some performance and allow the implementation on integrated circuits Another approach to increase the system’s power efficiency is to utilize the advantages of integrated circuitry based on digital building blocks [12]. DPD concepts have been proposed for RF-DAC-based transmitters [23]–[27] These published DPD systems use conventional black-box approaches to model and mitigate the nonlinear effects. The resulting mathematical models are based on the detailed analysis of the origin and the resulting effects of the nonlinearities of the RF-DAC design, resulting in low complexity, but powerful DPD approaches.
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