A Circuit-Inspired Digital Predistortion of Supply Network Effects for Capacitive RF-DACs

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. Index Terms-Digital predistortion (DPD), memory effects, memory polynomial (MP), power amplifier (PA), radio frequency digital-to-analog converter (RF-DAC), switched-capacitor power amplifier (SCPA), Volterra series. I. INTRODUCTION T HE demand for high data rates, robust transmissions, and power efficiency poses stringent requirements on the design of integrated wireless transceiver systems. Increasing the data rate, while simultaneously providing a reliable and power-efficient transmission, is closely related to the linearity of the communication systems. In radio frequency (RF) wireless communication transmitters, the key component in terms of linearity and Manuscript

A Predistortion-Less Digital MIMO Transmitter With DTC-Based Quadrature Imbalance Compensation

“…Code-dependent supply current will result in a voltage drop over Z supply , regardless of whether star connections to ground and the supply are used. As the SCPA is a DAC with its supply as reference voltage, this will result in nonlinear behavior [18], [19]. When multiple SCPAs are connected to the same power supply as in Fig.…”

“…The implementation based on switches and accurately matched capacitors makes it intrinsically highly linear [14]. This linearity is predominantly limited by the code-dependence output impedance [14], [17] and the quality of the power supply, as the supply voltage is the reference voltage for the RF-DAC [18]. Techniques to linearize the code-dependent output conductance have been proposed in [8] and [7], and a wideband low-impedance supply was proposed in [19].…”

Predistortion-Based Linearization for 5G and Beyond Millimeter-Wave Transceiver Systems: A Comprehensive Survey

“…Neural Network-Based Model Waveform Processing at Transmission and Observation Path [67], [81], [89]- [103] [110]- [120], [122], [123] [67], [75], [82]- [88] DAC and ADC nonidealities [29], [130], [133]- [141] RF Sub-Components Effects [130]- [132], [142], [145] [130], [131] Amplitude-Compensated Phase Shifter [78], [79], [148]- [155], [157], [158] Phase-Compensated and Low-Noise Variable Gain Amplifier [44], [149], [159]- [169] SVM-Based Model better output performance. Since the invention of wireless communication, the linearity of transmitting signals hold paramount importance [73], [74].…”

“…However, the massive distributions of IC connections in MIMO systems present unpredictable nonlinearities across the entire TRX subsystems, making it compulsory for the test signals to evade the sine waves offset [130]. In the opposite scenario, the causal dynamic drifts of the supply voltage hinder the desired ACPR and error vector magnitude (EVM) of the modulation signal [140], [141]. This strand emphasizes the importance of potent DPD structures, which should be adaptable to the inevitable dynamic effects and discontinuities of waveform magnitudes in distributed TRX systems.…”