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Pulse-Width Modulated RF Transmitters
Linköping University, Department of Electrical Engineering, Computer Engineering. Linköping University, Faculty of Science & Engineering.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The market for wireless portable devices has grown signicantly over the recent years.Wireless devices with ever-increased functionality require high rate data transmissionand reduced costs. High data rate is achieved through communication standards such asLTE and WLAN, which generate signals with high peak-to-average-power ratio (PAPR),hence requiring a power amplier (PA) that can handle a large dynamic range signal. Tokeep the costs low, modern CMOS processes allow the integration of the digital, analogand radio functions on to a single chip. However, the design of PAs with large dynamicrange and high eciency is challenging due to the low voltage headroom.

To prolong the battery life, the PAs have to be power-ecient as they consume a sizablepercentage of the total power. For LTE and WLAN, traditional transmitters operatethe PA at back-o power, below their peak efficiency, whereas pulse-width modulation(PWM) transmitters use the PA at their peak power, resulting in a higher efficiency.PWM transmitters can use both linear and SMPAs where the latter are more power efficient and easy to implement in nanometer CMOS. The PWM transmitters have a higher efficiency but suffer from image and aliasing distortion, resulting in a lower dynamic range,amplitude and phase resolution.

This thesis studies several new transmitter architectures to improve the dynamicrange, amplitude and phase resolution of PWM transmitters with relaxed filtering requirements.The architectures are suited for fully integrated CMOS solutions, in particular forportable applications.

The first transmitter (MAF-PWMT) eliminates aliasing and image distortions whileallowing the use of SMPAs by combining RF-PWM and band-limited PWM. The transmittercan be implemented using all-digital techniques and exhibits an improved linearity and spectral performance. The approach is validated using a Class-D PA based transmitter where an improvement of 10.2 dB in the dynamic range compared to a PWM transmitter for a 1.4 MHz of LTE signal is achieved.

The second transmitter (AC-PWMT) compensates for aliasing distortion by combining PWM and outphasing. It can be used with switch-mode PAs (SMPAs) or linear PAs at peak power. The proposed transmitter shows better linearity, improved spectral performanceand increased dynamic range as it does not suffer from AM-AM distortion of the PAs and aliasing distortion due to digital PWM. The idea is validated using push-pull PAs and the proposed transmitter shows an improvement of 9 dB in the dynamic rangeas compared to a PWM transmitter using digital pulse-width modulation for a 1.4 MHzLTE signal.

The third transmitter (MD-PWMT) is an all-digital implementation of the second transmitter. The PWM is implemented using a Field Programmable Gate Array(FPGA) core, and outphasing is implemented as pulse-position modulation using FPGA transceivers, which drive two class-D PAs. The digital implementation offers the exibility to adapt the transmitter for multi-standard and multi-band signals. From the measurement results, an improvement of 5 dB in the dynamic range is observed as compared to an all-digital PWM transmitter for a 1.4 MHz LTE signal.

The fourth transmitter (EP-PWMT) improves the phase linearity of an all-digital PWM transmitter using PWM and asymmetric outphasing. The transmitter uses PWM to encode the amplitude, and outphasing for enhanced phase control thus doubling the phase resolution. The measurement setup uses Class-D PAs to amplify a 1.4 MHz LTEup-link signal. An improvement of 2.8 dB in the adjacent channel leakage ratio is observed whereas the EVM is reduced by 3.3 % as compared to an all-digital PWM transmitter.

The fifth transmitter (CRF-ML-PWMT) combines multilevel and RF-PWM, whereas the sixth transmitter (CRF-MP-PMWT) combines multiphase PWM and RF-PWM. Both transmitters have smaller chip area as compared to the conventional multiphase and multilevel PWM transmitters, as a combiner is not required. The proposed transmitters also show better dynamic range and improved amplitude resolution as compared to conventional RF-PWM transmitters.

The solutions presented in this thesis aims to enhance the performance and simplify the digital implementation of PWM-based RF transmitters.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. , 78 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1822
National Category
Signal Processing Other Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications Communication Systems Computer Engineering
Identifiers
URN: urn:nbn:se:liu:diva-134023DOI: 10.3384/diss.diva-134023ISBN: 9789176855980 (print)OAI: oai:DiVA.org:liu-134023DiVA: diva2:1066473
Public defence
2017-02-23, John von Neumann, Hus B, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2017-01-18 Created: 2017-01-18 Last updated: 2017-04-27Bibliographically approved
List of papers
1. Combined RF and Multilevel PWM Switch Mode Power Amplifier
Open this publication in new window or tab >>Combined RF and Multilevel PWM Switch Mode Power Amplifier
2013 (English)In: Norchip, IEEE , 2013, 1-4 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a novel power amplifier (PA) architecture based on the combination of radio frequency pulse width modulation (RFPWM) and multilevel PWM. The architecture provides better dynamic range at high carrier frequency compared to RFPWM. The benefits of this architecture over multilevel PWM are that it only requires a single PA and no combiner. The average efficiency for an 802.11g baseband signal is better than multilevel PWM. Our results also shows that the proposed technique exhibit a constant dynamic range at carrier frequency of 3, 4 and 5 GHz, in contrast to RFPWM which shows a decrease in dynamic range for increase in carrier frequency.

Place, publisher, year, edition, pages
IEEE, 2013
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-102929 (URN)10.1109/NORCHIP.2013.6702010 (DOI)978-147991647-4 (ISBN)
Conference
NORCHIP 2013; Vilnius; Lithuania
Available from: 2014-01-08 Created: 2014-01-08 Last updated: 2017-01-18
2. Combined RF and Multiphase PWM Transmitter
Open this publication in new window or tab >>Combined RF and Multiphase PWM Transmitter
2015 (English)In: 2015 European Conference on Circuit Theory and Design (ECCTD), IEEE , 2015, 264-267 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents two novel transmitter architectures based on the combination of radio-frequency pulse-width modulation and multiphase pulse-width modulation. The proposed transmitter architectures provide good amplitude resolution and large dynamic range at high carrier frequency, which is problematic with existing radio-frequency pulse-width modulation based transmitters. They also have better power efficiency and smaller chip area compared to multiphase pulse-width modulation based transmitters.

Place, publisher, year, edition, pages
IEEE, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-122703 (URN)10.1109/ECCTD.2015.7299999 (DOI)000380498200001 ()978-1-4799-9877-7 (ISBN)
Conference
2015 European Conference on Circuit Theory and Design (ECCTD), Trondheim, Norway, August 24-26, 2015
Available from: 2015-11-16 Created: 2015-11-16 Last updated: 2017-01-18Bibliographically approved

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