Integrated millimeter Wave CMOS Power Amplifiers for 5G Systems

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Sammanfattning

The anticipated continuation of the last three decades of growth of global demand for high-speed high-coverage mobile data, calls for massive investments in cellular infrastructure, for the ongoing roll out of the fifth generation of mobile systems, but also later for the sixth generation. A key enabler, for the high-speed part, is for the cellular system to move up in frequency and support communication at millimeter-wave (mmW) frequencies (24 – 70 GHz), where available wideband spectrum exist. One of the most challenging building blocks for communication at mmW frequencies is the power amplifier, which has the function to amplify the transmission signal before feeding it to the antenna. The power amplifier should ideally provide high output power, without distorting the signal, while consuming as little power as possible. These requirements stand in stark contrast with each other and is particularly troublesome for high-speed communication at high frequencies. This dissertation is about mmW power amplifiers and it starts with introductory chapters, placing the power amplifier in its context and presenting theory about power amplifiers in general. Then follows a brief summary of the scientific contribution with conclusions and some suggestions for future work, of the four papers, which are the foundation of the dissertation.
Paper I presents a CMOS mmW power amplifier and pre-power amplifier, with aim for integration in an antenna array system. To increase the output power, while still reducing the maximum needed supply voltage, the circuit utilizes a ”two way” output combiner prior to the load. The PA, measured using continuous wave signals, reached, at the time, state-of-the-art performance for both saturated output power and 1 dB compression point, combined with low AM-PM distortion below the compression point.
Paper II describes a CMOS mmW Transmit/Receive (TRX)-switch, power amplifier, and pre-power amplifier, targeted for integration in an antenna array system. To linearise the output signal the PA input transistors gate bias is adjusted based on the input signal level, i.e. it uses adaptive bias. The TRX-switch provides a downward 1:2 impedance transformation in TX-mode to boost reachable output power, and in RX-mode it provides an upward impedance transformation of 2:1 for optimal noise figure. The adaptive bias brings significant improvement of both saturated output power and 1 dB output compression point, and simulations for the TRX-switch show low insertion loss in both TX and RX mode.
In Paper III a CMOS mmW transceiver front-end including a novel TRXswitch is presented. For high efficiency the transmitter is equipped with a Doherty PA, which uses a high bandwidth adaptive bias circuit to reduce the fundamental nonlinearity associated with Doherty PAs. In addition, an innovative method is implemented that breaks the fundamental bandwidth limitation for the input signal of Doherty PAs. The transceiver was extensively measured in both transmit and receive mode. In transmit mode, continuous wave as well as OFDM-modulated measurements were performed. State-of-the-art output power and efficiency for integrated transceivers for high bandwidth OFDM-modulated signals were demonstrated, and for the receiver state-of-the-art noise figure was achieved when compared in the same category. Significant improvements on ACLR and EVM when using the adaptive bias for wideband modulated signals were demonstrated. Furthermore, excellent image rejection ratio and LO leakage suppression were measured.
Paper IV derives fundamental equations related to a Doherty amplifier, using a simplified transistor model suitable for hand calculations, and thus the fundamental nonlinearity of the Doherty amplifier is explained and investigated. Furthermore, the paper analyses the use of adaptive bias, which offers the possibility to mitigate the fundamental nonlinearity as explained by the theory. To verify the theoretical predictions, the design and measurements of the adaptive bias circuit tailored for high PAR high bandwidth modulated signals, for the mmW Doherty amplifier in paper III, are presented in detail. Controllability of the adaptive bias circuit, which is needed to fully benefit from using adaptive bias, was measured using continuous wave tone stimuli. Multiple measurements with wideband OFDM-modulated signals were also conducted which largely verified the predictions by the theory. For increased reliability the measurements were repeated using two different samples.
Originalspråkengelska
KvalifikationDoktor
Handledare
  • Sjöland, Henrik, handledare
Tilldelningsdatum2024 apr. 19
UtgivningsortLund
Förlag
ISBN (tryckt)978-91-8039-944-9
ISBN (elektroniskt)978-91-8039-945-6
StatusPublished - 2024

Bibliografisk information

Defence details
Date: 2024-04-19
Time: 09:15
Place: Lecture Hall E:1406, building E, Ole Römers väg 3, Faculty of Engineering LTH, Lund University, Lund. The dissertation will be live streamed, but part of the premises is to be excluded from the live stream.
External reviewer(s)
Name: Pärssinen, Aarno
Title: Prof.
Affiliation: Oulu University, Finland.
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Ämnesklassifikation (UKÄ)

  • Inbäddad systemteknik

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