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1.
  • Amin, Shoaib, 1985-, et al. (författare)
  • Noise Impact on the Identification of DigitalPredistorter Parameters in the Indirect LearningArchitecture
  • 2012
  • Ingår i: 2012 Swedish Communication Technologies Workshop (Swe-CTW). - IEEE conference proceedings. - 978-1-4673-4763-1 ; s. 36-39
  • Konferensbidrag (refereegranskat)abstract
    • The indirect learning architecture (ILA) is the mostused methodology for the identification of Digital Pre-distorter(DPD) functions for nonlinear systems, particularly for highpower amplifiers. The ILA principle works in black box modelingrelying on the inversion of input and output signals of thenonlinear system, such that the inverse is estimated. This paperpresents the impact of disturbances, such as noise in the DPDidentification. Experiments were performed with a state-of-artDoherty power amplifier intended for base station operationin 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) canbe a misleading figure of merit showing improvement in theperformance for wrongly estimated DPD functions.
2.
  • Bjorsell, Niclas, et al. (författare)
  • Measuring Volterra kernels of analog to digital converters using a stepped three-tone scan
  • 2006
  • Ingår i: 2006 IEEE INSTRUMENTATION AND MEASUREMENT TECHNOLOGY CONFERENCE PROCEEDINGS. - 978-0-7803-9359-2 - 0-7803-9359-7 ; s. 1047-1050
  • Konferensbidrag (övrigt vetenskapligt)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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3.
  • Bjorsell, Niclas, et al. (författare)
  • Post-correction of under-sampled analog to digital converters
  • 2007
  • Ingår i: 2007 IEEE INSTRUMENTATION & MEASUREMENT TECHNOLOGY CONFERENCE. - 978-1-4244-0588-6 ; s. 58-62
  • Konferensbidrag (refereegranskat)abstract
    • Applications with wide bandwidth and high center frequencies force the analog to digital converter (ADC) to be active in a working range with less dynamic performance in relation to lower frequency bands. However using under-sampling techniques in combination with post-correction methods enable a combination of high sampling rate, wide bandwidth and low distortion. In this paper the employed dynamic post-correction is a combination of look-up tables and model based correction. The results are mainly based on measurements on a 12-bit 210 MSPS ADC. The improvement in total harmonic distortion and spurious free dynamic range are acceptable over a wide frequency range and it is robust to variations in amplitude.
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4.
  • Björsell, Niclas, et al. (författare)
  • A Statistical Evaluation of ADC Histogram Tests with Arbitrary Stimuli Signal
  • 2005
  • Ingår i: ADDA 2005. - 0 86341 542 3 ; s. 259-264
  • Konferensbidrag (refereegranskat)abstract
    • Histogram tests are a commonly used method for characterizing analogue to digital converters. However, different stimuli signals can be used in the histogram test. An overview of common input stimuli for the test is presented. Previous works have analysed the statistical properties of the resulting histograms for different stimuli signals, separately. In this paper, generally applicable results for asymptotically unbiased minimum variance estimator and Cramer-Rao lower bound are derived, irrespective of used input stimuli. Where available, the general expression is compared and found in accordance with signal-specific expressions.
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5.
  • Björsell, Niclas, et al. (författare)
  • Achievable ADC Performance by Post-Correction Utilizing Dynamic Modeling of the Integral Nonlinearity
  • 2008
  • Ingår i: EURASIP Journal on Advances in Signal Processing. - 1110-8657. ; s. 497187-1-497187-10
  • Tidskriftsartikel (refereegranskat)abstract
    • There is a need for a universal dynamic model of analog-to-digital converters (ADC’s) aimed for postcorrection. However, it is complicated to fully describe the properties of an ADC by a single model. An alternative is to split up the ADC model in different components, where each component has unique properties. In this paper, a model based on three components is used, and a performance analysis for each component is presented. Each component can be postcorrected individually and by the method that best suits the application. The purpose of postcorrection of an ADC is to improve the performance. Hence, for each component, expressions for the potential improvement have been developed. The measures of performance are total harmonic distortion (THD) and signal to noise and distortion (SINAD), and to some extent spurious-free dynamic range (SFDR).
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6.
  • Björsell, Niclas, et al. (författare)
  • Analog-to-Digital Converters for High-Speed Applications
  • 2005
  • Ingår i: GigaHz 2005. ; s. 151-154
  • Konferensbidrag (refereegranskat)abstract
    • There is a rapid development of the performance of state-of-the-art analog to digital converters (ADC). Resolution and sampling rate are increasing continuously. Sampling rates in the high intermediate frequency (IF) range with sufficient dynamic range for communication applications were introduced about the turn of the millennium. Post-correction methods enable fast ADCs with modest linearity, and thereby weak dynamic performance, for high-speed applications.A post-correction procedure involves a characterization of the ADC non-linearity and then utilizing this information by processing the ADC output samples to remove the distortion. ADC characterization is usually performed by estimating ADC characteristics from measurements. Consequently, successful characterizations require both developed test methods and high performance test-beds.Characterization and testing ADCs are interesting in many different aspects. Not only that a proper characterization can be used for error compensation, testing is a major factor of cost for manufacturers, and shortening of the test cycle implies large savings. Testing ADCs is complicated, time consuming and demands high-performance instrumentation.
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7.
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8.
  • Björsell, Niclas, et al. (författare)
  • Dynamic behavior models of analog to digital converters aimed for post-correction in wideband applications
  • 2006
  • Ingår i: IMEKO Workshop on ADC and DAC Modelling and Testing.
  • Konferensbidrag (refereegranskat)abstract
    • In this paper a dynamic behavior model of analog to digital converters is proposed. The model is aimed for post correction in wideband applications. The suggested post correction method is a combination of look up tables and model based correction.The model consists of three components. The first is a component represented by a Hammerstein model; that is a static nonlinearity followed by a time invariant linear filter. The second component is a nonparametric model caused by significant deviation from the characterized integral nonlinearity and the output from the Hammerstein model. The third component contains of the remaining deviation and is considered as a random model error.Results from simulations verify that the examined ADC can be described by an ordinary Hammerstein model and a static look-up table.
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9.
  • Björsell, Niclas, et al. (författare)
  • High Dynamic Range Test Bed for Characterization of Analogue-To-Digital Converters up to 500 MSPS
  • 2005
  • Konferensbidrag (refereegranskat)abstract
    • A measurement set-up of for the characterization of analog-to-digital converters (ADCs) isdescribed. The measurement set-up characterizes ADCs up to 16 bits at 350 MHz (option for >500MHz). Testing dynamic performance of high-speed ADCs is regarded as difficult and expensive. Byusing existing state-of-the-art instruments in combination with specially designed amplifiers and filters,a high performance, cost efficient test-bed has been built-up. Practical performance corresponds to ADCdatasheet and exceeds the performance obtained if using commercial instruments only. Consequently,the measurement results represent the true performance of the ADC without impact from the test-bed.
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10.
  • Björsell, Niclas, et al. (författare)
  • Histogram Tests for Wideband Applications
  • 2008
  • Ingår i: IEEE Transactions on Instrumentation and Measurement. - 0018-9456. ; 57:1, s. 70-75
  • Tidskriftsartikel (refereegranskat)abstract
    • Characterization and testing of analog-to-digital converters (ADCs) are important for many reasons. A histogram test is a common method to characterize the linearity features of an ADC. Two commonly used stimulus signals are sine waves and Gaussian noise. This paper presents a metrological comparison between Gaussian and sine-wave histogram tests for wide-band applications, that is, we evaluate the performance of the characterization of the ADC and the usability of postcorrection. A postcorrection procedure involves the characterization of the ADC nonlinearity and then the use of this information by processing the ADC output samples to remove the distortion. The results show that the Gaussian histogram test gives reasonable accuracy in measuring nonlinearities. However, it does not result in a suitable model for postcorrection in wideband applications. A single-tone sine-wave histogram will be a better basis for postcorrection. The best result can be obtained if the lookup table is trained with several single-tone sine waves in the frequency band.
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