Transmitter Linearization for mm-Wave Communications Systems

There is an ever increasing need for enabling higher data rates in modern communication systems which brings new challenges in terms of the power consumption and nonlinearity of hardware components. These problems become prominent in power amplifiers (PAs) and can significantly degrade the performance of transmitters, and hence the overall communication system. Hence, it is of central importance to design efficient PAs with a linear operation region. This thesis proposes a methodology and a comprehensive framework to address this challenge. This is accomplished by application of predistortion to a mm-wave PA and an E-band IQ transmitter while investigating the trade-offs between linearity, efficiency and predistorter complexity using the proposed framework.In the first line of work, we have focused on a mm-wave PA. A PA has high efficiency at high input power at the expense of linearity, whereas it operates linearly for lower input power levels while sacrificing efficiency. To attain both linearity and efficiency, predistortion is often used to compensate for the PA nonlinearity. Yet, the trade-offs related to predistortion complexities are not fully understood. To address this challenge, we have used our proposed framework for evaluation of predistorters using modulated test signals and implemented it using digital predistortion and a mm-wave PA. This set-up enabled us to investigate the trade-offs between linearity, efficiency and predistorter complexity in a systematic manner. We have shown that to achieve similar linearity levels for different PA classes, predistorters with different complexities are needed and provided guidelines on the achievable limits in term linearity for a given predistorter complexity for different PA classes.In the second line of work, we have focused on linearization of an E-band transmitter using a baseband analog predistorter (APD) and under constraints given by a spectrum emission standard. In order to use the above proposed framework with these components, characterizations of the E-band transmitter and the APD are performed. In contrast to typical approaches in the literature, here joint mitigation of the PA and I/Q modulator impairments is used to model the transmitter. Using the developed models, optimal model parameters in terms of output power at the mask limit are determined. Using these as a starting point, we have iteratively optimized operating point of the APD and linearized the E-band transmitter. The experiments demonstrated that the analog predistorter can successfully increase the output power by 35% (1.3 dB) improvement while satisfying the spectrum emission mask

Improvement of AM-PM in a 33-GHz CMOS SOI Power Amplifier Using pMOS Neutralization

This letter presents two highly efficient two-stage power amplifiers (PAs) for 5G applications, implemented in a 22-nm slilicon on insulator (SOI) CMOS technology. High efficiency is achieved by carefully designing the power cells and optimizing the layout. Capacitive neutralization is used to improve the stability and the gain. Both PAs are similar except for the use of nMOS neutralization capacitors in the first one. In the second PA, we propose the use of pMOS capacitors instead to enhance significantly both stability and AM-PM linearity at the same time. For both PAs, the saturated output power is 12.7 dBm andP1 dB is 11.9 dBm from a 0.9-V supply at 33 GHz with a power-added efficiency (PAE) at P1 dB of more than 36%. The PAE at Psat is 38% and 40% for the PA with nMOS and pMOS neutralizations, respectively. The AM-PM up to P3 dB for the PA with nMOS neutralization is 7, and for the one with pMOS neutralization, it is less than 1.3 thanks to the proposed technique