A novel digital-intensive hybrid transmitter (TX) architecture is presented, combining conventional inphase and quadrature (I/Q) with constrained phase modulation. The proposed architecture utilizes an RF-DAC with phase modulated RF clock and adjusted I/Q components. By incorporating phase modulation the quadrature component is kept small while the inphase component approaches the complex signal envelope. Compared to a digital-quadrature TX architecture this results in a significantly reduced average and peak RF-DAC cell utilization. Therefore, the RF-DAC can be operated in less backoff at higher average output power and drain efficiency. The phase modulation is constrained in order to relax the phase modulators system requirements. Compared to a digital polar TX architecture utilizing an RF digital phase-locked loop with two-point phase modulation, this results in reduced frequency modulation and digital-controlled oscillator tuning range requirements. In addition, the design effort is further shifted from analog to digital domain in order to better exploit the benefits of CMOS technology scaling. Index Terms-Wireless communication, digital polar transmitter, digital quadrature transmitter, hybrid polar-I/Q transmitter, phase modulation, quadrature modulation, RF digital-to-analog converter (RF-DAC), RF digital power amplifier (RF-DPA), RF digital phase-locked loop (RF-DPLL). I. INTRODUCTION W IRELESS transceivers for multi-band, multi-standard mobile handset applications operating in the sub-6 GHz range are usually implemented in ultra-deep
This article presents an overview of the major trends and challenges involved with the design of multi-band, multi-standard digitallyintensive radio frequency transceivers for next generation mobile communications. In addition, we discuss in detail one aspect of the implementation challenges, namely the occurrence and cancellation of self-interference especially in carrier aggregation modes. For that, we present a novel digital cancellation technique to jointly compensate the self-interference caused by transmit (Tx) modulated spurs and Tx second order intermodulation distortion products (IMD2) in the receiver. This architecture exploits the underlying relation between both types of interference and offers a low-complexity solution to mitigate the Tx-IMD2 interference. Simulation results show, that the proposed technique significantly suppresses both types of interference and restores the signal-to-noise ratio of the wanted signal within 0.3 dB from its value in the absence of interference, thereby achieving 30 dB of cancellation.Keywords: RF; mobile communications; wireless communications; signal processing; interference cancellation; carrier aggregation Digital unterstützte Hochfrequenz-Transceiver für den Mobilfunk der Zukunft -Trends und Herausforderungen. Dieser Artikel gibt zunächst einen Überblick über aktuellen Trends und Herausforderungen bei der Entwicklung von Multi-Band, Multi-Standard HF-Transceivern für die nächste Mobilfunk-Generation, die einen hohen Anteil an digitaler Elektronik aufweisen. Im Anschluss wird im Detail auf ein spezielles Problem solcher Transceiver eingegangen, nämlich der Selbst-Interferenz, die durch den eigenen Sender verursacht wird und die vor allem im Carrier Aggregation-Modus auftritt. Die Problematik wird nicht nur detailliert erklärt, diese Arbeit präsentiert auch eine Methode zur Unterdrückung von Selbst-Interferenz mit den Mitteln der digitalen
Cellular standards evolve to support increasingly higher bandwidths which results in strict in-and out-of-band requirements such as lower error vector magnitude (EVM) and/or adjacent channel leakage ratio (ACLR). Digital polar transmitters, which are showing the best performance in terms of power consumption, are challenged to fulfill these requirements. This work will show that even in case of ideal analog components and infinite digital resources, there are principle limitations in terms of out-of-band noise for digital polar transmitters. A typical polar modulation will be compared to a theoretical signal with continuous amplitude modulation. The analysis of the resulting error signal suggests a decomposition into two components which can be partially compensated in the amplitude and phase modulation paths. Based on that decomposition a compensation algorithm has been developed and evaluated with a 400 MHz 5G New Radio (NR) signal for Band n257 on Frequency Range 2 with carrier frequency of 26.5 GHz. The compensation results in an out-of-band noise reduction of 44 dB close to the carrier frequency. Furthermore, EVM improvements for NR signals are demonstrated.
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