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| 2. |
- Björsell, Niclas, et al.
(author)
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Kautz-Volterra modelling of an analogue-to-digital converter using a stepped three-tone excitation
- 2007
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In: 12th IMEKO TC-4 International Workshop on ADC MODELLING AND TESTING. ; , s. 107-112
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Conference paper (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. 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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| 3. |
- Björsell, Niclas, et al.
(author)
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Measuring Volterra kernels of analog to digital converters using a stepped three-tone scan
- 2006
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In: Proceedings of the IEEE Instrumentation and Measurement Technology Conference, 2006. IMTC 2006. - 0780393597 ; , s. 1047-1050
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Conference paper (peer-reviewed)abstract
- Volterra theory can be used to mathematically model nonlinear dynamic components such as analog-to-digital converter (ADC). This paper describes how frequency domain Volterra kernels of an ADC are determined from measurements. The elements of Volterra theory are given and practical issues are considered, such as methods for signal conditioning, finding the appropriate test signals scenario and suitable sampling frequency. The results show that for the used pipeline ADC, the frequency dependence is significantly stronger for second order difference products than for sum products and the linear frequency dependence was not as pronounced as that of the second order Volterra kernel.
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| 4. |
- Björsell, Niklas, et al.
(author)
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Measuring Volterra Kernels of Analog To Digital Converters Using a Stepped Three-Tone Scan
- 2008
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In: IEEE Transactions on Instrumentation and Measurement. - 0018-9456 .- 1557-9662. ; 57:4, s. 666-671
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Journal article (peer-reviewed)abstract
- The Volterra theory can be used to mathematically model nonlinear dynamic components such as analog-to-digital converters (ADCs). This paper describes how frequency-domain Volterra kernels of an ADC are determined from measurements. The elements of the Volterra theory are given, and practical issues are considered, such as methods for signal conditioning and finding the appropriate test signals scenario and suitable sampling frequency. The results show that, for the used pipeline ADC, the frequency dependence is significantly stronger for second-order difference products than for sum products and the linear frequency dependence was not as pronounced as that of the second-order Volterra kernel. It is suggested that the Volterra kernels have the symmetry properties of a specific box model, namely, the parallel Hammerstein system.
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| 5. |
- Feng, X. M., et al.
(author)
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Image analysis for monitoring the barley tempeh fermentation process
- 2007
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In: Journal of Applied Microbiology. - Oxon, United Kingdom : Oxford University Press (OUP). - 1364-5072 .- 1365-2672. ; 103:4, s. 1113-1121
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Journal article (peer-reviewed)abstract
- Aims: To develop a fast, accurate, objective and nondestructive method for monitoring barley tempeh fermentation. Methods and Results: Barley tempeh is a food made from pearled barley grains fermented with Rhizopus oligosporus. Rhizopus oligosporus growth is important for tempeh quality, but quantifying its growth is difficult and laborious. A system was developed for analysing digital images of fermentation stages using two image processing methods. The first employed statistical measures sensitive to image colour and surface structure, and these statistical measures were highly correlated (r = 0.92, n = 75, P < 0.001) with ergosterol content of tempeh fermented with R. oligosporus and lactic acid bacteria (LAB). In the second method, an image-processing algorithm optimized to changes in images of final tempeh products was developed to measure number of visible barley grains. A threshold of 5 visible grains per Petri dish indicated complete tempeh fermentation. When images of tempeh cakes fermented with different inoculation levels of R. oligosporus were analysed the results from the two image processing methods were in good agreement. Conclusion: Image processing proved suitable for monitoring barley tempeh fermentation. The method avoids sampling, is nonintrusive, and only requires a digital camera with good resolution and image analysis software. Significance and Impact of the Study: The system provides a rapid visualization of tempeh product maturation and qualities during fermentation. Automated online monitoring of tempeh fermentation by coupling automated image acquisition with image processing software could be further developed for process control.
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| 6. |
- 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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| 7. |
- Isaksson, Magnus, 1969-, et al.
(author)
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A Kautz-Volterra Behavioral Model for RF Power Amplifiers
- 2006
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In: IEEE MTT-S International Microwave Symposium Digest, 2006. - 0780395417 ; , s. 485-488
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Conference paper (peer-reviewed)abstract
- A new type of behavioral power amplifier (PA) model, a discrete-time Kautz-Volterra (KV) model, is presented. In the model a priori knowledge of the system properties in terms of different poles for different nonlinear orders is used, which is needed for modeling nonlinear and linear memory effects in PAs. An accurate model can thus be achieved with a small number of parameters. Simulated results of parallel Hammerstein and Wiener structures and from modeling the behavior of a PA are presented
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| 8. |
- 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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| 9. |
- Isaksson, Magnus, 1969-, et al.
(author)
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A Study of a Variable-Capacitance Drain Network's Influence on Dynamic Behavioral Modeling of an RF PA
- 2007
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In: 69th ARFTG Microwave measurement conference, Honolulu, HI, USA. ; , s. 112-116, s. 5456336-
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Conference paper (peer-reviewed)abstract
- An investigation of the complex-valued parameters of two different dynamic behavioral models due to changes in the drain decoupling network of a PA has been performed. The study is based on complex-envelope measurements on a real PA. The complex coefficients of the parallel Hammerstein (PH) and the optimal pole placements of the Kautz-Volterra (KV) models are analyzed. It is concluded that the parameters follow smooth, predictable functions and that the KV poles give a robust description of the PA's memory effects compared with the PH model.
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