Abstract-This paper presents a behavioral model structure and a model-based phase-only predistortion method suitable for outphasing RF amplifiers. The predistortion method is based on a model of the amplifier with a constant gain factor and phase rotation for each outphasing signal, and a predistorter with phase rotation only. The method has been used for EDGE and WCDMA signals applied to a Class-D outphasing RF amplifier with an on-chip transformer used for power combining in 90nm CMOS. The measured peak power at 2 GHz was +10.3 dBm with a drain efficiency and power-added efficiency of 39 % and 33 %, respectively. For an EDGE 8-PSK signal with a phase error of 3• between the two input outphasing signals, the measured power at 400 kHz offset was -65.9 dB with predistortion, compared to -53.5 dB without predistortion. For a WCDMA signal with the same phase error between the input signals, the measured ACLR at 5 MHz offset was -50.2 dBc with predistortion, compared to -38.0 dBc without predistortion.
This paper considers the problem of wear estimation in a standard industrial robot joint. Motivated by the observation that the wear processes in a robot actuator cause an increase of the friction levels in the joint, static friction observations are used to infer the wear levels. An existing static friction model is extended to include the eects of wear, which are analyzed and modeled. The resulting model can explain friction in a robot joint with respect to changes in speed, load, temperature and wear. Based on this model and a test-cycle that generates static friction observations, a modelbased wear estimator is proposed. The performance of the estimator is found both by means of simulations and experiments on an industrial robot. As it is shown, the method can distinguish the eects of wear even under large temperature variations, opening up for the use of robust joint diagnosis for industrial robots. Abstract: This paper considers the problem of wear estimation in a standard industrial robot joint. Motivated by the observation that the wear processes in a robot actuator cause an increase of the friction levels in the joint, static friction observations are used to infer the wear levels.An existing static friction model is extended to include the effects of wear, which are analyzed and modeled. The resulting model can explain friction in a robot joint with respect to changes in speed, load, temperature and wear. Based on this model and a test-cycle that generates static friction observations, a model-based wear estimator is proposed. The performance of the estimator is found both by means of simulations and experiments on an industrial robot. As it is shown, the method can distinguish the effects of wear even under large temperature variations, opening up for the use of robust joint diagnosis for industrial robots.
Abstract-This paper considers the problem of how to estimate a model of the inverse of a system. The use of inverse systems can be found in many applications, such as feedforward control and power amplifier predistortion. The inverse model is here estimated with the purpose of using it in cascade with the system itself, as an inverter. A good inverse model in this setting would be one that, when used in series with the original system, reconstructs the original input. The goal here is to select suitable inputs, experimental conditions and loss functions to obtain a good input estimate. Both linear and nonlinear systems will be discussed.For nonlinear systems, one way to obtain a linearizing prefilter is by Hirschorn's algorithm. It is here shown how to extend this to the postdistortion case, and some formulations of how the pre-or postinverter could be estimated are also presented.
Abstract-This paper presents a model-based phase-only predistortion method suitable for outphasing radio frequency (RF) power amplifiers (PA). The predistortion method is based on a model of the amplifier with a constant gain factor and phase rotation for each outphasing signal, and a predistorter with phase rotation only. Exploring the structure of the outphasing PA, the model estimation problem can be reformulated from a nonconvex problem into a convex least-squares problem, and the predistorter can be calculated analytically. The method has been evaluated for 5 MHz Wideband Code-Division Multiple Access (WCDMA) and Long Term Evolution (LTE) uplink signals with Peak-to-Average Power Ratio (PAPR) of 3.5 dB and 6.2 dB, respectively, applied to one of the first fully integrated +30 dBm Class-D outphasing RF PA in 65nm CMOS. At 1.95 GHz for a 5.5 V (6.0 V) supply voltage, the measured output power of the PA was +29.7 dBm (+30.5 dBm) with a power-added efficiency (PAE) of 27 %. For the WCDMA signal with +26.0 dBm of channel power, the measured Adjacent Channel Leakage Ratio (ACLR) at 5 MHz and 10 MHz offsets were -46.3 dBc and -55.6 dBc with predistortion, compared to -35.5 dBc and -48.1 dBc without predistortion. For the LTE signal with +23.3 dBm of channel power, the measured ACLR at 5 MHz offset was -43.5 dBc with predistortion, compared to -34.1 dBc without predistortion.
Life is not easy. Finishing a PhD is not easy. One of the good things about the PhD is that you get a chance at the end to say thank you to the people who have helped you, which you might not get in life. This is my attempt to thank the ones who have helped me go through with this project. I'll start and end these acknowledgments with people without whom I think there would be no thesis (or not this, my thesis at least, others might still be able to write theirs). To my supervisor Dr. Martin Enqvist: I think I would have given up a long time ago if it wasn't for your encouragements. I am really impressed with how you always have time (or rather, take the time) to answer questions or concerns, and without feeling stressed. I know you have lots of other things to do and I really appreciate it. I also like how you can turn things around for a positive spin. Thank you for pushing me through this! Prof. Lennart Ljung and Prof. Torkel Glad, thanks for being co-supervisors and providing input. I should have talked, asked and learned more! I have had the pleasure of having three different bosses, who have all helped me sort out the work situation when life gets in the way. Prof. Lennart Ljung, Prof. Svante Gunnarsson and Dr. Martin Enqvist, you all seem to be able to guide the group forward as well as see the people and how to help. Lennart, thanks for letting me join the group! Svante, without your flexibility and willingness to adapt I could not have finished this thesis. Thank you! Martin, thanks for making every day bring-your-baby-to-work ! I am also grateful for the administrative help from Ninna Stensgård and her predecessor Åsa Karmelind. The upside of being on the slow side finishing your PhD is that you get to meet a lot of colleagues. I have really appreciated the Automatic control group and the amazing people in it! It is a group full of brilliant, fun, and hard working people, thank you all! I think my current office mate Kerstin is my favorite, but Patrik Leissner, Maryam Sadeghi Reineh and Gustaf Hendeby, you tie for second place (and you were all far less demanding)! Many colleagues I also consider friends and hope I will still see a lot of you in the future. Special shout outs to Manon Kok (for staying in touch and being a good friend), Daniel Petersson (for pepp and believing in me), Patrik Leissner (for friendship and helpfulness
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