| 1. |
- Landin, Per Niklas, 1983-, et al.
(author)
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Modeling and Digital Predistortion of Class-D Outphasing RF Power Amplifiers
- 2012
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In: IEEE transactions on microwave theory and techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 60:6, s. 1907-1915
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Journal article (peer-reviewed)abstract
- This paper presents a direct model structure for describing class-D outphasing power amplifiers (PAs) and a method for digitally predistorting these amplifiers. The direct model structure is based on modeling differences in gain and delay, nonlinear interactions between the two paths, and differences in the amplifier behavior. The digital predistortion method is designed to operate only on the input signals phases, to correct for both amplitude and phase mismatches. This eliminates the need for additional voltage supplies to compensate for gain mismatch. less thanbrgreater than less thanbrgreater thanModel and predistortion performance are evaluated on a 32-dBm peak-output-power class-D outphasing PA in CMOS with on-chip transformers. The excitation signal is a 5-MHz downlink WCDMA signal with peak-to-average power ratio of 9.5 dB. Using the proposed digital predistorter, the 5-MHz adjacent channel leakage power ratio (ACLR) was improved by 13.5 dB, from -32.1 to -45.6 dBc. The 10-MHz ACLR was improved by 6.4 dB, from -44.3 to -50.7 dBc, making the amplifier pass the 3GPP ACLR requirements.
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| 2. |
- Masud, Nauman, et al.
(author)
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On stability and performance of disturbance observer-based-dynamic load torque compensator for assistive exoskeleton : A hybrid approach
- 2020
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In: Mechatronics (Oxford). - : Elsevier. - 0957-4158 .- 1873-4006. ; 69
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Journal article (peer-reviewed)abstract
- A disturbance observer-based-dynamic load-torque compensator for current-controlled DC-drives, as joint actuator of assistive exoskeletons, has been recently proposed. It has been shown that this compensator can effectively linearize and decouple the coupled nonlinear dynamics of the human-exoskeleton system, by more effectively compensating the associated nonlinear load-torques of the exoskeleton at the joint level. In this paper, a detailed analysis of the current controlled DC drive-servo system using the said compensator, with respect to performance and stability is presented, highlighting the key factors and considerations affecting both the stability and performance of the compensated servo system. It is shown both theoretically and through simulation results that the stability of the compensated servo system is compromised as performance is increased and vice-versa. Based on the saturation state of the servo system, a new hybrid switching control strategy is then proposed to select stability or performance-based compensator and controller optimally. The strategy is then experimentally verified both at the joint and task space level by using the developed four active-degree of freedom exoskeleton test rig.
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| 3. |
- Landin, Per N., et al.
(author)
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Power Amplifier Behavioral Modeling Performance Comparison of the LSNA and the Modulation-Domain System
- 2008
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In: 72ND ARFTG MICROWAVE MEASUREMENT SYMPOSIUM - TIME DOMAIN AND FREQUENCY DOMAIN MEASUREMENT. - New York : IEEE. - 9781424422999 ; , s. 73-78, s. 73-78
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Conference paper (peer-reviewed)abstract
- The performance of power amplifier behavioral models depends strongly on the performance of the system used to measure the amplifiers. In this study two different systems with nonlinear measurement capability are used to model a commercially available PA. One system is a large-signal network analyzer (LSNA) and the second system is a modulation-domain system (MDS) consisting of a vector signal generator and a vector signal analyzer. The PA was tested with multitone and WCDMA signals and behavioral models were extracted from the measured data. The evaluation criteria normalized mean square error and weighted error spectral power ratio or adjacent channel error power ratio were then computed to compare the performance of the models from the two systems. Cross-validation between the systems, using data from one system to obtain the model and validating its performance with data from the other system, shows that the model performance is mainly affected by the used validation data. Validating the performance of models from the LSNA with data from the MDS indicates that the identified models have almost the same performance as the MDS-identified models, i.e. it does not matter which system is used to identify the models. Cross-validation using a WCDMA-signal and multitone signal from the different systems shows that the normalized mean square error is mainly affected by modeling imperfections introduced by using another signal type. WESPR and ACEPR show a certain difference in performance with somewhat lower values for the MDS. The behavior of the two systems can be explained by different noise levels.
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| 4. |
- Landin, Per N., et al.
(author)
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Two novel memory polynomial models for modeling of RF power amplifiers
- 2015
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In: International journal of microwave and wireless technologies. - 1759-0795 .- 1759-0787. ; 7:1, s. 19-29
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Journal article (peer-reviewed)abstract
- Two novel memory polynomial models are derived based on physical knowledge of a general power amplifier (PA). The derivations are given in detail to facilitate derivations of other model structures. The model error in terms of normalized mean square error (NMSE) and adjacent channel error power ratio (ACEPR) of the novel model structures are compared to that of established models based on the number of parameters using data measured on two different amplifiers, one high-power base-station PA and one low-power general purpose amplifier. The novel models show both lower NMSE and ACEPR for any chosen number of parameters compared to the established models. The low model errors make the novel models suitable candidates for both modeling and digital predistortion.
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| 5. |
- Alizadeh, Mahmoud, et al.
(author)
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A new Block-Structure Modeling Technique for RF Power Amplifiers in a 2×2 MIMO System
- 2017
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In: 2017 13th International Conference on Advanced Technologies, Systems and Services in Telecommunications, TELSIKS 2017 - Proceeding. - Nis, Serbia : IEEE. - 9781538618004 ; , s. 224-227
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Conference paper (peer-reviewed)abstract
- A new block-structure behavioral model is proposed for radio frequency power amplifiers in a 2×2 multiple-input multiple-output system including input cross-talk. The proposed model forms kernels of blocks of different nonlinear order that correspond to the significant frequency response of measured frequency domain Volterra kernels. The model can therefore well describe the input-output relationships of the nonlinear dynamic behavior of PAs. The proposed model outperforms conventional models in terms of model errors.
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| 6. |
- Amin, Shoaib, 1985-, et al.
(author)
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Concurrent dual-band power amplifier model modification using dual two-tone test
- 2016
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In: 46th European Microwave Conference (EUMC) 2016. - : Institute of Electrical and Electronics Engineers (IEEE). - 9782874870439 - 9781509015146 ; , s. 186-189
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Conference paper (peer-reviewed)abstract
- A dual two-tone technique for the characterization of memory effects in concurrent dual-band transmitters is revisited to modify a 2D-DPD model for the linearization of concurrent dual-band transmitters. By taking into account the individual nonlinear memory effects of the self- and cross-kernels, a new 2D modified digital pre-distortion (2D-MDPD) model is proposed, which not only supersedes the linearization performance but also reduces the computational complexity compared to the 2D-DP Dmodel in terms of a number of floating point operations (FLOPs). Experimental results show an improvement of 1.7 dBin normalized mean square error (NMSE) and a 58% reduction in the number of FLOPs.
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| 7. |
- Amin, Shoaib, 1985-, et al.
(author)
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Noise Impact on the Identification of Digital Predistorter Parameters in the Indirect Learning Architecture
- 2012
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In: 2012 Swedish Communication Technologies Workshop (Swe-CTW). - : IEEE conference proceedings. - 9781467347631 ; , s. 36-39
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Conference paper (peer-reviewed)abstract
- The indirect learning architecture (ILA) is the mostused methodology for the identification of Digital Pre-distorter (DPD) functions for nonlinear systems, particularly for high power amplifiers. The ILA principle works in black box modeling relying on the inversion of input and output signals of the nonlinear system, such that the inverse is estimated. This paper presents the impact of disturbances, such as noise in the DPD identification. Experiments were performed with a state-of-art Doherty power amplifier intended for base station operation in current telecommunication wireless networks. As expected, a degradation in the performance of the DPD (measured innormalized mean square error (NMSE)) is found in our experiments. However, adjacent channel power ratio (ACPR) can be a misleading figure of merit showing improvement in the performance for wrongly estimated DPD functions.
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| 8. |
- Björsell, Niclas, et al.
(author)
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Kautz-Volterra modelling of analogue-to-digital converters
- 2010
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In: Computer Standards & Interfaces. - : Elsevier BV. - 0920-5489 .- 1872-7018. ; 32:3, s. 126-129
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Journal article (peer-reviewed)abstract
- In many test and measurement applications, the analogue-to-digital converter (ADC) is the limiting component. Using post-correction methods can improve the performance of the component as well as the over all measurement system. In this paper an ADC is characterised by a Kautz-Volterra (KV) model, which utilises a model-based post-correction of the ADC with general properties and a reasonable number of parameters. It is also shown that the inverse model has the same dynamic properties as the direct KV model. Results that are based on measurements on a high-speed 12-bit ADC, shows good results for a third order model.
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| 9. |
- Isaksson, Magnus, 1969-, et al.
(author)
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A Comparative Analysis of Behavioral Models for RF Power Amplifiers
- 2006
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In: IEEE transactions on microwave theory and techniques. - 0018-9480 .- 1557-9670. ; 54:1, s. 348-359
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Journal article (peer-reviewed)abstract
- A comparative study of nonlinear behavioral models with memory for radio-frequency power amplifier (PAs) is presented. The models are static polynomial, parallel Hammerstein (PH), Volterra, and radial basis-function neural network (RBFNN). Two PAs were investigated: one was designed for the third-generation (3G) mobile telecommunication systems and one was designed for the second-generation (2G). The RBFNN reduced the total model error slightly more than the PH, but the error out of band was significantly lower for the PH. The Volterra was found to give a lower model error than did a PH of the same nonlinear order and memory depth. The PH could give a lower model error than the best Volterra, since the former could be identified with a higher nonlinear order and memory depth. The qualitative conclusions are the same for the 2G and 3G PAs, but the model errors are smaller for the latter. For the 3G PA, a static polynomial gave a low model error as low as the best PH and lower than the RBFNN for the hardest cross validation. The models with memory, PH, and RBFNN, showed better cross-validation performance, in terms of lower model errors, than a static polynomial for the hardest cross validation of the 2G PA.
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| 10. |
- Isaksson, Magnus, et al.
(author)
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A Parameter-Reduced Volterra Model for Dynamic RF Power Amplifier Modeling based on Orthonormal Basis Functions
- 2007
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In: International Journal of RF and Microwave Computer-Aided Engineering. - : Hindawi Limited. - 1096-4290 .- 1099-047X. ; 17:6, s. 542-551
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Journal article (peer-reviewed)abstract
- A nonlinear dynamic behavioral model for radio frequency power amplifiers is presented. It uses orthonormal basis functions, Kautz functions, with complex poles that are different for each nonlinear order. It has the same general properties as Volterra models, but the number of parameters is significantly smaller. Using frequency weighting the out-of-band model error can be reduced. Using experimental data it was found that the optimal poles were the same for different input powers and for the different nonlinear orders. The optimal poles were also the same for direct and inverse models, which could be explained theoretically to be a general property of nonlinear systems with negligible linear memory effects. The model can be used as either a direct or inverse model with the same model error for power amplifiers with negligible linear memory effects.
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